Superior Mesenteric Artery Syndrome

Structural MONDO:0002687 Pathograph 15 Show in embeddings browser Duodenal Obstruction

Superior mesenteric artery (SMA) syndrome, also called Wilkie syndrome or cast syndrome, is a rare mechanical cause of proximal (high) small-bowel obstruction in which the third, horizontal part of the duodenum is compressed in the narrowed space between the abdominal aorta and vertebral column posteriorly and the superior mesenteric artery anteriorly. Its mechanism is anatomic and biomechanical rather than Mendelian: the retroperitoneal/mesenteric fat pad that normally cushions the SMA and holds it away from the aorta is depleted by catabolic weight loss (or the aortomesenteric geometry is distorted by corrective spinal surgery, body casting, or rapid linear growth), narrowing the aortomesenteric angle and distance until the duodenum is trapped. The resulting obstruction causes postprandial pain, nausea, and vomiting, which reduce oral intake and drive further weight loss and further fat-pad depletion - a self-amplifying vicious cycle that is the defining pathophysiologic feature of the disorder and the reason nutritional restoration, not symptom suppression, is the therapeutic target.

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8
Pathophys.
13
Phenotypes
1
Hypotheses
2
Gaps
15
Pathograph
6
Medical Actions
3
Differentials
5
Trials
14
References
1
Deep Research
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Classifications

Harrison's Part
GASTROINTESTINAL
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Mechanistic Hypotheses

1
Self-amplifying fat-pad-depletion cycle
fat_pad_depletion_vicious_cycle CANONICAL
Evidence balance 1 support
The canonical model of SMA syndrome is not a simple linear cascade but a positive-feedback loop. Depletion of the aortomesenteric fat pad narrows the aortomesenteric angle and compresses the duodenum; the resulting meal-provoked pain, nausea, and vomiting reduce oral intake; the reduced intake produces further weight loss and further fat-pad depletion, which narrows the angle still further. Edges tagged with this hypothesis group form the closed cycle (fat-pad depletion -> angle narrowing -> duodenal compression -> obstruction -> reduced intake -> weight loss -> fat-pad depletion). The clinical corollary is that the loop can only be broken by restoring the fat pad (nutritional rehabilitation, ideally delivered distal to the obstruction) or by surgically bypassing the compressed segment.
Pathograph links
Mesenteric Fat Pad Depletion -> Aortomesenteric Angle and Distance Narrowing DIRECT
Aortomesenteric Angle and Distance Narrowing -> Extrinsic Compression of the Third Part of the Duodenum DIRECT
Extrinsic Compression of the Third Part of the Duodenum -> Proximal Duodenal Obstruction and Gastroduodenal Stasis DIRECT
Proximal Duodenal Obstruction and Gastroduodenal Stasis -> Meal-Provoked Symptoms and Reduced Oral Intake DIRECT
Meal-Provoked Symptoms and Reduced Oral Intake -> Progressive Weight Loss and Malnutrition DIRECT
Progressive Weight Loss and Malnutrition -> Mesenteric Fat Pad Depletion DIRECT The closing edge of the vicious cycle. Obstruction-driven weight loss further depletes the very fat pad whose loss caused the obstruction, so the aortomesenteric angle narrows further and the disease becomes self-sustaining unless nutrition is restored or the segment is bypassed.
Show evidence (1 reference)
PMID:31998513 SUPPORT Human Clinical
"The symptoms that patients experience lead to further decreases in oral intake, which in turn brings about further weight and fat pad loss and thus worsening of the duodenal obstruction."
States the positive-feedback structure explicitly - symptoms reduce intake, which worsens fat-pad loss, which worsens the obstruction.
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Discussions and Knowledge Gaps

2
Is there any molecular, genetic, or cellular determinant of susceptibility to SMA syndrome, beyond bulk visceral adiposity and skeletal geometry?
KNOWLEDGE GAP OPEN smas_no_molecular_lesion
Attached to
pathophysiology#Mesenteric Fat Pad Depletion
SMA syndrome is curated here as a purely biomechanical disorder with no causal gene, pathogenic variant, inheritance pattern, molecular biomarker, or omics signature established. Yet only a minority of severely underweight patients develop it, implying unmodelled determinants of susceptibility - for example constitutional differences in the fixation and length of the ligament of Treitz, in SMA origin height or take-off angle, in the regional lipolytic behaviour of the mesenteric fat depot versus other depots, or in mesenteric connective-tissue laxity. Rare familial reports exist but have not been resolved to a mechanism. Whether these determinants are anatomic-variant, connective-tissue, or adipose-biology in nature is entirely open.
Proposed experiments
Depot-resolved mesenteric adipose mobilisation study
smas_depot_lipolysis
Depot-resolved imaging or adipose sampling asking whether the mesenteric fat depot is preferentially mobilised in patients who develop SMA syndrome compared with BMI-matched controls who do not.
Decision criterion
Preferential mesenteric-depot loss in cases versus matched controls would support a depot-specific adipose-biology determinant of susceptibility.
Prospective pre/post weight-loss aortomesenteric geometry cohort
smas_pre_post_geometry
Prospective CT or ultrasound cohorts measuring aortomesenteric angle, aortomesenteric distance, SMA origin height, and ligament-of-Treitz position before and after comparable weight loss, to identify pre-existing geometric predisposition.
Decision criterion
Baseline geometric parameters that predict incident SMA syndrome independently of the magnitude of weight loss would establish anatomic predisposition.
Connective-tissue phenotyping of SMA syndrome cohorts
smas_connective_tissue_phenotyping
Systematic assessment of joint hypermobility and established heritable connective-tissue disease in SMA syndrome cohorts versus controls.
Decision criterion
Enrichment of connective-tissue laxity in cases would implicate mesenteric connective-tissue properties as a susceptibility determinant.
What aortomesenteric angle and distance thresholds should define SMA syndrome, and should they be adjusted for age, BMI, sex, population, and imaging technique?
KNOWLEDGE GAP OPEN smas_threshold_variability
Attached to
pathophysiology#Aortomesenteric Angle and Distance Narrowing
One population-specific cross-sectional series reported a mean aortomesenteric angle of 54.07 +/- 8.53 degrees and a mean distance of 16.25 +/- 3.44 mm, while a prospective clinical cohort used 22 degrees or less and 8 mm or less as operational thresholds. Because the angle and distance correlate directly with BMI - which is itself the disease's principal risk factor - a fixed threshold necessarily entangles the exposure with the diagnostic criterion, and narrowed geometry occurs in asymptomatic individuals. Population- and age-specific normative studies are actively being conducted but have not yet produced adjusted criteria.
Proposed experiments
Multi-population normative aortomesenteric reference study
smas_normative_multipopulation
Normative CT and ultrasound studies across multiple populations, stratified by age, sex, BMI, and measured visceral fat, deriving percentile-based rather than fixed thresholds.
Decision criterion
Demonstration that percentile-based, covariate-adjusted thresholds outperform a single fixed cut-off would justify replacing the current criteria.
Prospective diagnostic-accuracy study of candidate thresholds
smas_threshold_accuracy
Prospective study comparing candidate angle and distance thresholds against a reference standard combining compatible symptoms with demonstrated duodenal transit obstruction, reporting sensitivity, specificity, and positive predictive value.
Decision criterion
A threshold pair with acceptable positive predictive value against the composite reference standard would define operational diagnostic criteria.
Show evidence (4 references)
PMID:30291587 SUPPORT Human Clinical
"The diagnosis was achieved through barium swallow, CT/MR angiography (aortomesenteric angle ≤ 22°, distance ≤ 8 mm), endoscopy."
Documents the operational angle and distance thresholds used in a prospective clinical cohort.
PMID:38694377 SUPPORT Human Clinical
"Understanding these normal values in the Nepalese population is critical for accurate diagnoses and predictions using CT scans. The research highlights the impact of demographic factors on these parameters and emphasizes their significance in clinical assessments related to SMA syndrome."
Argues explicitly that population-specific normative aortomesenteric values are needed rather than a single universal threshold.
clinicaltrials:NCT03937193 SUPPORT Human Clinical
"In literature, superior mesenteric artery (SMA) angle, also named as aortomesenteric angle (AMA), varies greatly in both adult and children; while the aortomesenteric distance also ranges widely. Both AMA and AMD are influenced by retroperitoneal fat."
Registered normative study confirming both the wide literature variation in aortomesenteric geometry and its confounding by retroperitoneal fat - the two halves of this knowledge gap.
+ 1 more reference
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Pathophysiology

8
Precipitating Catabolic Weight Loss or Anatomic Alteration
The upstream trigger. Two mechanistically distinct routes converge on the same aortomesenteric geometry. (1) A catabolic/undernutrition state producing rapid or substantial weight loss - anorexia nervosa and other restrictive eating, malignancy and cachexia, major burns, trauma, malabsorption, chronic infection, prolonged immobilisation, or severe systemic illness. (2) A change in the spatial relationship among the spine, aorta, SMA, and duodenum without primary fat loss - corrective spinal surgery for scoliosis (the classic paediatric setting), body casting (the origin of the name "cast syndrome"), rapid linear growth, or abdominal/retroperitoneal operations that alter intestinal fixation and tension. A third, less common route is constitutional: a congenital anatomic variant of the SMA origin (an abnormally low, caudally angled take-off) or of duodenal fixation (a short, high-inserting ligament of Treitz suspending the duodenum within the aortomesenteric window) can narrow the window from birth, so that a much smaller degree of fat loss is sufficient to precipitate obstruction.
Downstream
Mesenteric Fat Pad Depletion Catabolic weight loss mobilises the visceral adipose stores that constitute the aortomesenteric cushion.
Aortomesenteric Angle and Distance Narrowing
Show evidence (2 references)
PMID:17476104 SUPPORT Human Clinical
"Frequently, predisposing medical conditions associated with catabolic states or rapid weight loss result in a decrease of the aortomesenteric angle and subsequent duodenal obstruction. External cast compression, anatomic variants and surgical alteration of the anatomy following spine surgery or..."
Names all three arms of the trigger node - catabolic/weight-loss states, mechanical/surgical alteration of the anatomy, and anatomic variants - and links them to the narrowed aortomesenteric angle.
PMID:29204239 SUPPORT Human Clinical
"This syndrome can be congenital or acquired. The acquired type is more common and is generally caused by reduced perivascular fat surrounding the abdominal aorta and the superior mesenteric artery"
Establishes the congenital/constitutional arm as a distinct (if less common) route alongside the acquired, fat-loss-driven form.
Mesenteric Fat Pad Depletion
Loss of the retroperitoneal and mesenteric adipose cushion that surrounds the origin of the superior mesenteric artery. In health this fat pad splays the SMA away from the aorta and provides the space through which the third part of the duodenum passes. Its depletion by lipolysis during negative energy balance is the proximate anatomic lesion of the weight-loss arm of the disease, and its reconstitution is the therapeutic goal of conservative management.
Self-amplifying fat-pad-depletion cycle
Visceral (mesenteric) white adipocyte CL:0000448 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Visceral (mesenteric) white adipocyte, annotated with white adipocyte (CL:0000448). CL:0000448 is a cell type from the Cell Ontology.
Triglyceride mobilization from the mesenteric fat depot GO:0006642 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased Triglyceride mobilization from the mesenteric fat depot, annotated with triglyceride mobilization (GO:0006642). GO:0006642 is a biological process from the Gene Ontology. ↑ INCREASED
Aortomesenteric (retroperitoneal) fat pad UBERON:0015143 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Aortomesenteric (retroperitoneal) fat pad, annotated with mesenteric fat pad (UBERON:0015143). UBERON:0015143 is an anatomical location from the Uberon multi-species anatomy ontology. Visceral abdominal adipose tissue UBERON:0014454 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Visceral abdominal adipose tissue (UBERON:0014454). UBERON:0014454 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Aortomesenteric Angle and Distance Narrowing Self-amplifying fat-pad-depletion cycle
Show evidence (1 reference)
PMID:31998513 SUPPORT Human Clinical
"The mesentery around the SMA is surrounded by a fatty tissue pad which forms a cushion that allows the duodenum to pass unobstructed between the SMA and the aorta."
Describes the normal function of the fat pad whose depletion defines this pathophysiology node.
Aortomesenteric Angle and Distance Narrowing
Reduction of the angle at which the SMA leaves the abdominal aorta, and of the aorta-to-SMA distance at the level of the duodenum. Normative values vary by population; one cross-sectional series reported a mean angle of 54.07 +/- 8.53 degrees and a mean distance of 16.25 +/- 3.44 mm. The operational diagnostic thresholds used in the largest prospective surgical series are an aortomesenteric angle of 22 degrees or less and/or a distance of 8 mm or less. This is a geometric, not a biochemical, lesion: no vascular occlusion, thrombosis, dissection, or ischaemia is involved, and the SMA itself is structurally normal.
Self-amplifying fat-pad-depletion cycle
Superior mesenteric artery UBERON:0001182 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Superior mesenteric artery (UBERON:0001182). UBERON:0001182 is an anatomical location from the Uberon multi-species anatomy ontology. Abdominal aorta UBERON:0001516 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Abdominal aorta (UBERON:0001516). UBERON:0001516 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Extrinsic Compression of the Third Part of the Duodenum Self-amplifying fat-pad-depletion cycle
Show evidence (2 references)
PMID:30291587 SUPPORT Human Clinical
"The diagnosis was achieved through barium swallow, CT/MR angiography (aortomesenteric angle ≤ 22°, distance ≤ 8 mm), endoscopy."
Gives the operational angle and distance thresholds used to define the narrowed aortomesenteric geometry in a prospective 39-patient cohort.
PMID:38694377 SUPPORT Human Clinical
"The study reveals a mean AMA of 54.07°±8.53° and a mean distance of 16.25±3.44 mm. Elevated BMI is found to positively correlate with AMA and distance, indicating that higher BMI values may augment these parameters"
Provides normative aortomesenteric angle/distance values and demonstrates the quantitative dependence of both parameters on BMI, the population-level counterpart of the fat-pad-depletion mechanism.
Extrinsic Compression of the Third Part of the Duodenum
The primary lesion. The horizontal (third) portion of the duodenum, which crosses the midline in the aortomesenteric window, is squeezed between the SMA anteriorly and the aorta and vertebral column posteriorly. The compression is extrinsic - the duodenal wall and lumen are intrinsically normal - which is why endoscopy alone cannot establish the diagnosis and why bypassing or decompressing the segment relieves it.
Self-amplifying fat-pad-depletion cycle
Third (horizontal) part of the duodenum UBERON:0002114 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Third (horizontal) part of the duodenum, annotated with duodenum (UBERON:0002114). UBERON:0002114 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Proximal Duodenal Obstruction and Gastroduodenal Stasis Self-amplifying fat-pad-depletion cycle
Show evidence (2 references)
PMID:31998513 SUPPORT Human Clinical
"It is defined as the extrinsic compression of the third part of the duodenum by the aorta posteriorly and the superior mesenteric artery anteriorly."
Defines the primary anatomic lesion, including the anterior and posterior compressing structures.
PMID:17476104 SUPPORT Human Clinical
"The syndrome is caused by compression of the third part of the duodenum in the angle between the aorta and the superior mesenteric artery."
Independent review confirming the site and mechanism of compression.
Proximal Duodenal Obstruction and Gastroduodenal Stasis
Partial or complete high intestinal obstruction at the third part of the duodenum. Chyme cannot pass the compressed segment, so the proximal duodenum and stomach dilate and empty slowly. Obstruction may be intermittent and posture-dependent - supine positioning worsens it and left lateral decubitus, prone, or knee-chest positions can transiently relieve it - which explains both the fluctuating symptoms and the positional manoeuvres used in conservative management.
Self-amplifying fat-pad-depletion cycle
Gastroduodenal emptying GO:0035483 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Gastroduodenal emptying, annotated with gastric emptying (GO:0035483). GO:0035483 is a biological process from the Gene Ontology. ↓ DECREASED
Duodenum UBERON:0002114 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Duodenum (UBERON:0002114). UBERON:0002114 is an anatomical location from the Uberon multi-species anatomy ontology. Stomach UBERON:0000945 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Stomach (UBERON:0000945). UBERON:0000945 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Meal-Provoked Symptoms and Reduced Oral Intake Self-amplifying fat-pad-depletion cycle
Show evidence (1 reference)
PMID:30291587 SUPPORT Human Clinical
"Barium swallow showed a gastroduodenal dilation in 57% of patients, and a delayed gastroduodenal emptying in 38%."
Quantifies proximal dilation and delayed emptying, the direct functional consequences of the compressed duodenal segment, in a prospective cohort.
Meal-Provoked Symptoms and Reduced Oral Intake
Eating loads the obstructed segment, producing postprandial epigastric pain, nausea, early satiety, bloating, and vomiting that begins within roughly 15-20 minutes of a meal and is characteristically relieved by emesis. Patients learn to avoid solids, then to avoid eating, so the obstruction is converted into a behavioural restriction of intake. This is the node at which a mechanical lesion becomes a nutritional one, and it is the hinge of the vicious cycle.
Self-amplifying fat-pad-depletion cycle
Downstream
Progressive Weight Loss and Malnutrition Self-amplifying fat-pad-depletion cycle
Obstructive and Aspiration Complications
Show evidence (1 reference)
PMID:37383896 SUPPORT Human Clinical
"The symptoms are variable, consisting of postprandial abdominal pain, nausea and vomiting, early satiety, anorexia, and weight loss and can mimic anorexia nervosa or functional dyspepsia."
Lists the meal-provoked symptom cluster and notes that it can be mistaken for a primary eating disorder, which is why intake falls.
Progressive Weight Loss and Malnutrition
Sustained negative energy balance with falling BMI, dehydration, and electrolyte and acid-base disturbance (classically hypochloraemic metabolic alkalosis from recurrent vomiting). In the largest prospective series the median BMI at presentation was 17.8 kg/m2, and surgical relief of the obstruction raised it significantly - consistent with the undernutrition being substantially driven by the obstruction rather than merely preceding it, though that series was single-arm and uncontrolled with concurrent nutritional care.
Self-amplifying fat-pad-depletion cycle
Downstream
Mesenteric Fat Pad Depletion The closing edge of the vicious cycle. Obstruction-driven weight loss further depletes the very fat pad whose loss caused the obstruction, so the aortomesenteric angle narrows further and the disease becomes self-sustaining unless nutrition is restored or the segment is bypassed. Self-amplifying fat-pad-depletion cycle
Show evidence (1 reference)
PMID:30291587 SUPPORT Human Clinical
"Thirty-nine patients (11 M/28 F, median age 38 years, median BMI 17.8 kg/m2) were included."
Documents the low BMI characteristic of the malnutrition node in a prospectively enrolled SMA syndrome cohort.
Obstructive and Aspiration Complications
Uncommon but potentially fatal sequelae of unrelieved obstruction and recurrent vomiting: aspiration pneumonia, respiratory depression from metabolic alkalosis, acute gastric dilatation progressing to necrosis and perforation, peptic ulceration, and obstructive acute pancreatitis. These complications are the reason delayed diagnosis carries meaningful mortality.
Show evidence (1 reference)
PMID:37383896 SUPPORT Human Clinical
"Because recurrent vomiting leads to aspiration pneumonia or respiratory depression via metabolic alkalosis, early diagnosis is required."
Names the aspiration and metabolic-alkalosis complications and the diagnostic urgency they create.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Superior Mesenteric Artery Syndrome Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

13
Digestive 5
Nausea HP:0002018 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nausea (HP:0002018). HP:0002018 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"Superior mesenteric artery syndrome is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, anorexia and weight loss."
Nausea is listed among the characterising symptoms.
Vomiting HP:0002013 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Postprandial bilious vomiting, annotated with Vomiting (HP:0002013). HP:0002013 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23959808 SUPPORT Human Clinical
"Common symptoms associated with this syndrome include intermittent postprandial abdominal pain, nausea, and bilious vomiting."
Identifies the vomiting as postprandial and bilious, consistent with an obstruction distal to the ampulla.
Early Satiety HP:0033842 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Early satiety (HP:0033842). HP:0033842 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37383896 SUPPORT Human Clinical
"The symptoms are variable, consisting of postprandial abdominal pain, nausea and vomiting, early satiety, anorexia, and weight loss and can mimic anorexia nervosa or functional dyspepsia."
Early satiety is listed in the core symptom cluster.
Anorexia HP:0002039 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Loss of appetite, annotated with Anorexia (HP:0002039). HP:0002039 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"Superior mesenteric artery syndrome is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, anorexia and weight loss."
Anorexia is listed among the characterising symptoms.
Malnutrition HP:0004395 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Malnutrition (HP:0004395). HP:0004395 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:31998513 SUPPORT Human Clinical
"Superior mesenteric artery (SMA) syndrome is a rare complication of severe malnutrition that leads to intestinal obstruction"
Links severe malnutrition directly to the obstruction, supporting malnutrition as an integral clinical feature.
Immune 1
Aspiration Pneumonia HP:0011951 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Aspiration pneumonia (HP:0011951). HP:0011951 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37383896 SUPPORT Human Clinical
"Because recurrent vomiting leads to aspiration pneumonia or respiratory depression via metabolic alkalosis, early diagnosis is required."
Directly identifies aspiration pneumonia as a consequence of the recurrent vomiting caused by the obstruction.
Growth 1
Weight Loss HP:0001824 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Weight loss (HP:0001824), qualified as course progressive. HP:0001824 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"Superior mesenteric artery syndrome is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, anorexia and weight loss."
Weight loss is listed among the characterising features.
Other 6
Postprandial Epigastric Pain HP:0410019 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Postprandial epigastric pain, annotated with Epigastric pain (HP:0410019). HP:0410019 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"Superior mesenteric artery syndrome is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, anorexia and weight loss."
Names postprandial epigastric pain as a defining feature of the syndrome.
High Intestinal Obstruction HP:0005250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Duodenal (high intestinal) obstruction, annotated with High intestinal obstruction (HP:0005250). HP:0005250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30291587 SUPPORT Human Clinical
"Superior mesenteric artery syndrome (SMAS) is a rare cause of duodenal obstruction, resulting from the compression of the duodenum between superior mesenteric artery and aorta."
Establishes duodenal obstruction as the defining clinical abnormality of the disease.
Low Body Mass Index Decreased body mass index HP:0045082 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Decreased body mass index (HP:0045082). HP:0045082 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30291587 SUPPORT Human Clinical
"SMAS is a rare condition that should be suspected in cases of chronic, refractory upper digestive symptoms, particularly in females with low BMIs."
Identifies low BMI as a characteristic feature of the affected population.
Hypochloremic Metabolic Alkalosis HP:0005977 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypochloremic metabolic alkalosis (HP:0005977). HP:0005977 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37383896 SUPPORT Human Clinical
"Because recurrent vomiting leads to aspiration pneumonia or respiratory depression via metabolic alkalosis, early diagnosis is required."
Identifies vomiting-induced metabolic alkalosis, and the respiratory depression it causes, as a recognised consequence of the obstruction.
Gastric Perforation HP:6000383 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Gastric perforation (HP:6000383). HP:6000383 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:31998513 SUPPORT Human Clinical
"they can show complications of this syndrome, such as acute gastric dilatation."
Documents acute gastric dilatation as a recognised complication. The progression from dilatation to perforation is not asserted by this source, so support is recorded as PARTIAL.
Acute Pancreatitis HP:0001735 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Acute pancreatitis (HP:0001735). HP:0001735 is a phenotype from the Human Phenotype Ontology.
Reported in the SMA syndrome complication literature and surfaced by the Edison deep-research report, but no PMID with a quotable abstract sentence linking acute pancreatitis to SMA syndrome was located, so no evidence item is asserted. Retained as a described but unevidenced complication rather than dropped.
💊

Medical Actions

6
Nutritional Rehabilitation and Weight Restoration
Action: nutritional supportNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is nutritional support (NCIT:C15433). NCIT:C15433 is a clinical intervention from the NCI Thesaurus. Ontology label: Nutritional Support NCIT:C15433
First-line and mechanistically definitive therapy. The goal is to restore the aortomesenteric fat pad, which widens the angle and relieves the compression - not merely to suppress nausea. Delivered as small, frequent, energy-dense liquid or soft feeds when oral intake is tolerated, with careful electrolyte monitoring for refeeding syndrome. Conservative management succeeds in roughly 70-80% of cases.
Mechanism Target:
RESTORES Mesenteric Fat Pad Depletion — Weight restoration reconstitutes the aortomesenteric fat pad, reversing the upstream anatomic lesion and breaking the vicious cycle at its origin.
Show evidence (2 references)
PMID:31998513 SUPPORT Human Clinical
"Treatment of SMA syndrome necessitates gaining enough weight to ultimately reconstitute the fat pad between the aorta and the SMA"
States that the therapeutic mechanism is reconstitution of the fat pad, i.e. reversal of the Mesenteric Fat Pad Depletion node.
PMID:29204239 SUPPORT Human Clinical
"After diagnosis, the patient followed a high-calorie diet, and 2 months later an ultrasound scan proved the restoration of the aorto-mesenteric angle as a consequence of increased perivascular fat with regression of symptoms."
Direct in-vivo demonstration of the treatment mechanism - refeeding restored the perivascular fat, which restored the aortomesenteric angle, which resolved the symptoms - closing the causal loop in the therapeutic direction.
Show evidence (1 reference)
PMID:37383896 SUPPORT Human Clinical
"The initial treatment is usually conservative, including postural change, gastroduodenal decompression, and nutrient management (success rates: 70%-80%)."
Establishes conservative nutritional/decompressive management as first line and quantifies its success rate.
Post-Pyloric (Nasojejunal) Enteral Feeding
Action: enteral tube feedingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is enteral tube feeding (NCIT:C93322). NCIT:C93322 is a clinical intervention from the NCI Thesaurus. Ontology label: Enteral Tube Feeding NCIT:C93322
Enteral nutrition delivered by a tube whose tip lies distal to the compressed third part of the duodenum. This bypasses the obstruction so that calories can be delivered despite it, allowing weight gain and fat-pad reconstitution - an intervention that exploits the fact that the bowel distal to the compression is entirely normal.
Mechanism Target:
BYPASSES Proximal Duodenal Obstruction and Gastroduodenal Stasis — Feeding distal to the compressed segment circumvents the obstruction rather than relieving the compression itself.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"first-line treatment is usually conservative with jejunal or parenteral nutrition for restoration of the aortomesenteric fatty tissue."
Identifies jejunal (post-pyloric) feeding as first-line conservative therapy aimed specifically at restoring the aortomesenteric fat.
Total Parenteral Nutrition
Action: total parenteral nutritionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is total parenteral nutrition (NCIT:C29484). NCIT:C29484 is a clinical intervention from the NCI Thesaurus. Ontology label: Total Parenteral Nutrition NCIT:C29484
Used when enteral feeding distal to the obstruction is impossible or insufficient, or when the obstruction is complete. Provides calories for weight restoration entirely independently of the gut.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"first-line treatment is usually conservative with jejunal or parenteral nutrition for restoration of the aortomesenteric fatty tissue."
Names parenteral nutrition alongside jejunal feeding as conservative therapy aimed at restoring the aortomesenteric fat pad.
Nasogastric Decompression
Action: nasogastric decompressionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is nasogastric decompression (NCIT:C70910). NCIT:C70910 is a clinical intervention from the NCI Thesaurus. Ontology label: Nasogastric Decompression NCIT:C70910
Gastroduodenal decompression relieves acute distension, reduces vomiting and aspiration risk, and allows correction of fluid and electrolyte deficits during the acute presentation. Symptomatic rather than mechanism-reversing.
Show evidence (1 reference)
PMID:28356803 SUPPORT Human Clinical
"The SMAS was suspected and a nasogastric tube was inserted, stomach decompression and the correction of electrolytes disbalance were made."
Documents nasogastric decompression plus electrolyte correction as the acute management of post-scoliosis-surgery SMA syndrome.
Laparoscopic Duodenojejunostomy
Action: laparoscopic duodenojejunostomyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is laparoscopic duodenojejunostomy, annotated with Laparoscopic Surgery (NCIT:C15725). NCIT:C15725 is a clinical intervention from the NCI Thesaurus. Ontology label: Laparoscopic Surgery NCIT:C15725
The best-supported definitive operation when conservative management fails. A side-to-side anastomosis between the duodenum proximal to the compression and the jejunum bypasses the aortomesenteric window entirely, so the obstruction is circumvented rather than the angle corrected. Reported success rates are 80-100%; in a prospective 39-patient cohort symptom scores fell and BMI rose significantly at a median 47 months of follow-up.
Mechanism Target:
BYPASSES Extrinsic Compression of the Third Part of the Duodenum — Diverts chyme around the compressed duodenal segment without altering the aortomesenteric geometry.
Show evidence (3 references)
PMID:30291587 SUPPORT Human Clinical
"At a median follow-up of 47 months, the overall symptom score significantly dropped (10 vs. 32, p < 0.0001) and BMI increased (19.5 vs. 17.8, p < 0.0001)."
Quantifies symptom and BMI improvement after duodenojejunostomy in the largest prospective cohort.
PMID:39191411 SUPPORT Human Clinical
"All operations were successfully completed laparoscopically, and with a median follow-up of 65 months, the overall symptom score was significantly reduced from 32 to 8 (p < 0.0001) and the BMI was increased from 17.2 kg/m2 to 21.8 kg/m2 (p < 0.0001)."
Independent 66-patient laparoscopic series confirming durable symptom and BMI improvement.
PMID:37383896 SUPPORT Human Clinical
"If conservative therapy fails, surgical treatment (i.e., laparoscopic duodenojejunostomy) is recommended (success rates: 80%-100%)."
Positions laparoscopic duodenojejunostomy as the recommended operation after failed conservative therapy and gives its success rate.
Strong Procedure (Division of the Ligament of Treitz)
Action: surgical procedureNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is surgical procedure (NCIT:C15329). NCIT:C15329 is a clinical intervention from the NCI Thesaurus. Ontology label: Surgical Procedure NCIT:C15329
Division of the ligament of Treitz with mobilisation of the duodenum allows the duodenum to drop caudally out of the narrowed aortomesenteric window. Unlike duodenojejunostomy this addresses the position of the duodenum relative to the compressing structures rather than bypassing the segment; it is anatomically distinct from duodenojejunostomy and less consistently effective.
Mechanism Target:
INHIBITS Extrinsic Compression of the Third Part of the Duodenum — Mobilising the duodenum out of the aortomesenteric window relieves the extrinsic compression directly.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"If conservative management fails, surgical options include open or laparoscopic duodenojejunostomy or duodenal mobilization and division of the ligament of Treitz."
Names duodenal mobilisation with division of the ligament of Treitz as a surgical option distinct from duodenojejunostomy.
🌍

Environmental Factors

3
Rapid or Substantial Weight Loss
Any catabolic or undernutrition state producing rapid loss of visceral fat - anorexia nervosa and other restrictive eating disorders, malignancy and cachexia, burns, trauma, malabsorption, chronic infection, and prolonged severe illness. This is the commonest precipitant.
Show evidence (1 reference)
PMID:31998513 SUPPORT Human Clinical
"SMA syndrome can be the result of a multitude of medical conditions that lead to weight loss and a malnourished state, namely wasting diseases such as cancer, burns, AIDS, and chronic infections; malabsorptive states; or voluntary or involuntary lack of caloric intake such as patients with..."
Enumerates the weight-loss states that precipitate SMA syndrome.
Mechanism Target:
TRIGGERS Precipitating Catabolic Weight Loss or Anatomic Alteration — Catabolic or undernutrition states directly establish the weight-loss arm of the precipitating mechanism.
Show evidence (1 reference)
PMID:31998513 SUPPORT Human Clinical
"SMA syndrome can be the result of a multitude of medical conditions that lead to weight loss and a malnourished state, namely wasting diseases such as cancer, burns, AIDS, and chronic infections; malabsorptive states; or voluntary or involuntary lack of caloric intake such as patients with..."
Directly links catabolic and undernutrition conditions to the weight-loss state that precipitates SMA syndrome.
Corrective Spinal Surgery for Scoliosis
surgical procedure exposure ECTO:2000054 Environmental Conditions, Treatments and Exposures Ontology (ECTO) Relation: this environmental factor is this exposure This environmental factor is surgical procedure exposure, annotated with exposure to surgery (ECTO:2000054). ECTO:2000054 is an exposure from the Environmental Conditions, Treatments and Exposures Ontology.
Surgical correction of a spinal deformity is a well-recognised precipitant, particularly in adolescents with adolescent idiopathic scoliosis and a low preoperative BMI. Reported latency to symptom onset diverges markedly between the two pooled systematic reviews - a mean of 9.6 +/- 9.5 days in one and a mean of 69 days (range 3 days to 4 years) in the other - so onset can be anywhere from the first postoperative days to years later, and a late presentation does not exclude the diagnosis.
Show evidence (3 references)
PMID:39118170 SUPPORT Human Clinical
"Superior mesenteric artery syndrome (SMAS) is a rare and unpredictable complication after correction spine surgery for adolescent idiopathic scoliosis (AIS)."
Establishes corrective spine surgery for adolescent idiopathic scoliosis as a recognised precipitating exposure.
PMID:39118170 SUPPORT Human Clinical
"The mean interval between spine surgery and symptoms of SAMS was 69 days, with high between-studies variability (3 days to 4 years)."
Gives the longer latency estimate that diverges from the 9.6-day mean of the other pooled review, documenting the wide and uncertain time-to-onset window.
PMID:33905850 SUPPORT Human Clinical
"The mean age of patients with SMA syndrome following scoliosis surgery was 14.7 ± 2.9 years and the majority (n = 42, 80.8%) were girls. The most frequently reported scoliosis type was adolescent idiopathic scoliosis (n = 34, 65.4%). The mean postoperative days (POD) (interval between the..."
Quantifies the demographics and post-operative latency of the scoliosis-surgery arm across 52 pooled cases.
Mechanism Target:
TRIGGERS Precipitating Catabolic Weight Loss or Anatomic Alteration — Corrective spine surgery directly supplies the anatomic-alteration arm of the precipitating mechanism, which then narrows the aortomesenteric geometry without requiring primary fat-pad depletion.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"External cast compression, anatomic variants and surgical alteration of the anatomy following spine surgery or ileoanal pouch anastomosis can also precipitate the syndrome."
Explicitly identifies surgical alteration after spine surgery as a precipitating route to SMA syndrome.
Body Casting and External Spinal Compression
Application of a body cast or spinal traction for scoliosis - the origin of the historical name "cast syndrome" - can precipitate the same duodenal compression without primary fat loss.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"External cast compression, anatomic variants and surgical alteration of the anatomy following spine surgery or ileoanal pouch anastomosis can also precipitate the syndrome."
Names external cast compression and anatomic/surgical alteration as precipitants distinct from weight loss.
Mechanism Target:
TRIGGERS Precipitating Catabolic Weight Loss or Anatomic Alteration — External cast compression directly supplies the mechanical-alteration arm of the precipitating mechanism.
Show evidence (1 reference)
PMID:17476104 SUPPORT Human Clinical
"External cast compression, anatomic variants and surgical alteration of the anatomy following spine surgery or ileoanal pouch anastomosis can also precipitate the syndrome."
Explicitly identifies external cast compression as a precipitant of SMA syndrome.
🔬

Diagnosis

1
Clinical-Radiological Concordance
Diagnosis requires BOTH a compatible obstructive clinical picture AND imaging evidence of duodenal compression with narrowed aortomesenteric geometry. A narrow angle or distance in isolation occurs in asymptomatic individuals and is not diagnostic; conversely, endoscopy cannot establish an extrinsic compression. In practice barium swallow, contrast-enhanced CT or CT/MR angiography, and endoscopy are combined.
Show evidence (2 references)
PMID:30291587 SUPPORT Human Clinical
"The diagnosis was achieved through barium swallow, CT/MR angiography (aortomesenteric angle ≤ 22°, distance ≤ 8 mm), endoscopy."
Describes the multimodal diagnostic pathway and the imaging thresholds applied.
PMID:23959808 SUPPORT Human Clinical
"CT angiography is currently favored in the literature for diagnosis as it can not only show the narrowed aorto-mesenteric angle and distance, but also the extent of duodenal obstruction."
Explains why CT angiography is preferred - it captures both the geometry and the obstruction, i.e. both halves of the concordance requirement.
🩻

Imaging Findings

2
Reduced Aortomesenteric Angle on CT Angiography
Sagittal reconstruction of contrast-enhanced abdominal CT (or CT/MR angiography) measures the angle at which the SMA leaves the aorta. Values of 22 degrees or less, together with an aortomesenteric distance of 8 mm or less, are the operational diagnostic criteria used in the largest prospective series, in which the median measured angle was 11 degrees and the median distance 5 mm. A narrowed angle in the absence of demonstrated duodenal obstruction is not diagnostic.
Ct Diagnostic
Superior mesenteric artery UBERON:0001182 Uberon multi-species anatomy ontology (UBERON)
Show evidence (2 references)
PMID:30291587 SUPPORT Human Clinical
"Median aortomesenteric angle was 11° and distance was 5 mm."
Reports the measured aortomesenteric geometry in a prospectively enrolled SMA syndrome cohort, quantifying the imaging finding.
PMID:31127323 SUPPORT Human Clinical
"Imaging can assist in diagnosis by demonstrating characteristic findings of reduced aortomesenteric angle, reduced aortomesenteric distance, gastroduodenal distention, bowel caliber narrowing at the takeoff of the superior mesenteric artery from the aorta, as well as delayed gastric emptying or..."
Enumerates the characteristic imaging findings, including the reduced angle and distance and the caliber change at the SMA takeoff.
Gastroduodenal Distention with Abrupt Caliber Change at the SMA Crossing
On an upper gastrointestinal barium series the stomach and proximal duodenum are dilated with abrupt hold-up of contrast at the level where the SMA crosses the third part of the duodenum, and gastroduodenal emptying is delayed. Obstruction may be positional, improving in the prone or left lateral decubitus position under real-time fluoroscopy.
Other
Duodenum UBERON:0002114 Uberon multi-species anatomy ontology (UBERON)
Modality is recorded as OTHER because a barium/upper-GI series is fluoroscopic rather than plain-film projectional radiography, and ImagingModalityEnum has no FLUOROSCOPY value.
Show evidence (1 reference)
PMID:30291587 SUPPORT Human Clinical
"Barium swallow showed a gastroduodenal dilation in 57% of patients, and a delayed gastroduodenal emptying in 38%."
Quantifies gastroduodenal dilation and delayed emptying on barium swallow in a prospective cohort.
📈

Progression

4
Intermittent postprandial symptoms
Early phase. Compression is partial and posture-dependent; symptoms occur after larger or solid meals and remit between them. Weight is often still preserved.
Established obstruction with reduced intake and weight loss
The vicious cycle is engaged. Solids are avoided, then meals generally; weight and the aortomesenteric fat pad fall together, progressively narrowing the angle.
Severe nutritional and metabolic compromise or complications
Marked undernutrition, dehydration, and hypochloraemic metabolic alkalosis, with risk of aspiration pneumonia, acute gastric dilatation and perforation, and obstructive pancreatitis. This is the phase that carries mortality.
Recovery after fat-pad restoration or surgical bypass
Conservative management succeeds in roughly 70-80% of cases; laparoscopic duodenojejunostomy achieves 80-100% success when it fails. The course may remit with weight restoration, recur if weight is lost again, or remain chronic if obstruction and nutritional depletion continue to perpetuate one another.
Show evidence (1 reference)
PMID:37383896 SUPPORT Human Clinical
"The initial treatment is usually conservative, including postural change, gastroduodenal decompression, and nutrient management (success rates: 70%-80%). If conservative therapy fails, surgical treatment (i.e., laparoscopic duodenojejunostomy) is recommended (success rates: 80%-100%)."
Quantifies recovery rates for the conservative and surgical routes out of the obstructed state.
📊

Prevalence

1
Worldwide
Point Prevalence Rare
Estimated at 0.013%-3% of the general population from historical barium studies; the wide range reflects radiographic ascertainment in selected populations rather than a population registry, so no precise numeric rate is asserted here.
Show evidence (1 reference)
PMID:31998513 SUPPORT Human Clinical
"The overall prevalence of SMA syndrome is unknown; however, it is estimated to be 0.013%"
Source states the prevalence is unknown and gives only a wide barium-study-derived estimate, supporting a qualitative RARE class rather than a numeric rate.
🌍

Epidemiology

1
Demographics
Median age at presentation around 23 years (reported range 0-91 years), with a female predominance of roughly 3:2 and a peak in adolescents and young adults. In the scoliosis-surgery subgroup the mean age is about 15 years and over 80% of reported cases are girls.
Show evidence (2 references)
PMID:37383896 SUPPORT Human Clinical
"The median age of patients is 23 years old (range 0-91 years old) and predominant in females over males with a ratio of 3:2."
Gives the age distribution and sex ratio.
PMID:33905850 SUPPORT Human Clinical
"The mean age of patients with SMA syndrome following scoliosis surgery was 14.7 ± 2.9 years and the majority (n = 42, 80.8%) were girls."
Supplies the age and sex distribution of the scoliosis-surgery subgroup quoted in this epidemiology entry.
🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Superior Mesenteric Artery Syndrome:

Nutcracker Syndrome (Left Renal Vein Entrapment)
Overlapping Features The other clinical consequence of a narrowed aortomesenteric angle. The same geometry that traps the duodenum also traps the left renal vein, so the two entities share an anatomic substrate, are frequently co-reported, and can coexist in the same patient. They are nonetheless distinct diseases with distinct compressed structures and distinct presentations, and must not be conflated.
Distinguishing Features
  • Nutcracker syndrome compresses the LEFT RENAL VEIN and presents as a urologic/venous syndrome with haematuria, proteinuria, left flank pain, pelvic congestion, and left varicocele.
  • SMA syndrome compresses the THIRD PART OF THE DUODENUM and presents as a gastrointestinal obstructive syndrome with postprandial pain, vomiting, and weight loss.
Show evidence (1 reference)
PMID:29204239 SUPPORT Human Clinical
"The reduced angle compresses the structures situated between the aorta and the superior mesenteric artery, such as the duodenum and left renal vein; this can determine painful crises, intestinal subocclusions, and left varicocele."
Documents that the same narrowed aortomesenteric angle compresses both the duodenum and the left renal vein, establishing the shared substrate while distinguishing the two symptom complexes.
Anorexia Nervosa
Overlapping Features The most consequential differential. SMA syndrome mimics a restrictive eating disorder (food avoidance, low BMI, vomiting), AND anorexia nervosa is one of its commonest causes, so the two are bidirectionally confusable and frequently coexist. Attributing SMA-syndrome symptoms to the psychiatric diagnosis alone delays treatment and blocks weight restoration.
Distinguishing Features
  • In SMA syndrome food avoidance is secondary to reproducible meal-provoked pain relieved by emesis or postural change, and imaging shows duodenal obstruction with a narrowed aortomesenteric angle.
  • In uncomplicated anorexia nervosa there is a primary drive for thinness and fear of weight gain, and imaging shows no duodenal obstruction.
Show evidence (1 reference)
PMID:37383896 SUPPORT Human Clinical
"The symptoms are variable, consisting of postprandial abdominal pain, nausea and vomiting, early satiety, anorexia, and weight loss and can mimic anorexia nervosa or functional dyspepsia."
States explicitly that SMA syndrome can mimic anorexia nervosa.
Functional Dyspepsia and Gastroparesis
Overlapping Features Non-obstructive upper-gut motility and symptom disorders that produce overlapping postprandial pain, nausea, bloating, and early satiety. Gastroparesis frequently coexists with SMA syndrome in malnourished patients.
Distinguishing Features
  • Neither produces a fixed extrinsic caliber change at the third part of the duodenum or a narrowed aortomesenteric angle on cross-sectional imaging.
  • Neither shows the abrupt positional relief (prone, knee-chest, left lateral decubitus) characteristic of SMA syndrome.
Show evidence (2 references)
PMID:31998513 SUPPORT Human Clinical
"Concurrent gastroparesis was diagnosed clinically in all eight patients."
Documents that gastroparesis coexisted in every case of a confirmed SMA syndrome series, supporting coexistence rather than mutual exclusion and explaining why the two are hard to disentangle clinically.
PMID:37383896 SUPPORT Human Clinical
"The symptoms are variable, consisting of postprandial abdominal pain, nausea and vomiting, early satiety, anorexia, and weight loss and can mimic anorexia nervosa or functional dyspepsia."
Names functional dyspepsia as a condition SMA syndrome mimics.
🔬

Clinical Trials

5
NCT03416647 COMPLETED
Prospective single-institution registry of 39 consecutive SMA syndrome patients (2008-2016), all treated with duodenojejunostomy, with symptom score, BMI, and barium swallow reassessed at follow-up. Published as PMID:30291587.
Target Phenotypes: Duodenal (high intestinal) obstruction HP:0005250 Human Phenotype Ontology (HP) Relation: this clinical trial targets this phenotype This clinical trial targets Duodenal (high intestinal) obstruction, annotated with High intestinal obstruction (HP:0005250). HP:0005250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
clinicaltrials:NCT03416647 SUPPORT
"Between 2008 and 2016, 39 consecutive patients with chronic gastrointestinal symptoms and a diagnosis of SMAS were prospectively included in the study, in order to describe their demographic, clinical and outcome features. All patients underwent duodenojejunostomy."
Describes the prospective cohort and the uniform duodenojejunostomy intervention underpinning the surgical evidence base.
NCT06970093 RECRUITING
Randomised open-label comparison of one-anastomosis gastric bypass versus duodenojejunostomy for SMA syndrome, with 12-month symptom, nutritional, and quality-of-life endpoints. Addresses the near-absence of comparative surgical evidence.
Target Phenotypes: Postprandial bilious vomiting HP:0002013 Human Phenotype Ontology (HP) Relation: this clinical trial targets this phenotype This clinical trial targets Postprandial bilious vomiting, annotated with Vomiting (HP:0002013). HP:0002013 is a phenotype from the Human Phenotype Ontology. Weight loss HP:0001824 Human Phenotype Ontology (HP) Relation: this clinical trial targets this phenotype This clinical trial targets Weight loss (HP:0001824). HP:0001824 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
clinicaltrials:NCT06970093 SUPPORT
"This condition causes the duodenum to be squeezed between two arteries, leading to severe nausea, vomiting, and weight loss."
Confirms the trial targets the mechanical duodenal compression and its cardinal symptoms.
NCT03937193 COMPLETED
Completed 510-participant CT study establishing the normal range of aortomesenteric angle and distance in a young Chinese population and correlating both with retroperitoneal adipose tissue. Directly addresses the threshold-variability knowledge gap and provides population-level confirmation of the fat-pad mechanism.
Show evidence (1 reference)
clinicaltrials:NCT03937193 SUPPORT
"In literature, superior mesenteric artery (SMA) angle, also named as aortomesenteric angle (AMA), varies greatly in both adult and children; while the aortomesenteric distance also ranges widely. Both AMA and AMD are influenced by retroperitoneal fat."
Documents both the wide variation in reported normal aortomesenteric geometry and its dependence on retroperitoneal fat.
NCT04515251 RECRUITING
Prospective multicentre observational study deriving normative ultrasound aortomesenteric measurements in healthy children aged 10-15 years, the age band in which post-scoliosis-surgery SMA syndrome peaks. Paediatric reference standards remain under development.
Show evidence (1 reference)
clinicaltrials:NCT04515251 SUPPORT
"Multicenter, prospective, observational research project on children aged from 10 to 15 years old undergoing abdominal ultrasound examinations during routine clinical practice."
Confirms the study is deriving paediatric normative aortomesenteric ultrasound values in the relevant age band.
NCT07115472 RECRUITING
Single-group study of fluoxetine in refractory SMA syndrome with comorbid DSM-5 somatic symptom disorder - the only registered pharmacotherapy trial in this disease. IMPORTANT SCOPE CAVEAT - this treats a psychiatric comorbidity that may amplify symptom burden, NOT the anatomic compression, and must not be generalised to routine SMA syndrome management. It is recorded here because the hypothesis (that reducing somatic-symptom amplification can avert duodenojejunostomy) bears directly on the disease's symptom-driven vicious cycle.
Show evidence (1 reference)
clinicaltrials:NCT07115472 SUPPORT
"Can psychiatric intervention targeting SSD reduce the likelihood of requiring duodenojejunostomy in refractory SMAS?"
States the trial's scope - a psychiatric comorbidity intervention tested for its effect on the need for surgery, not a treatment of the compression itself.
{ }

Source YAML

click to show 
name: Superior Mesenteric Artery Syndrome
creation_date: "2026-08-01T17:30:00Z"
category: Structural
description: >
  Superior mesenteric artery (SMA) syndrome, also called Wilkie syndrome or cast
  syndrome, is a rare mechanical cause of proximal (high) small-bowel obstruction
  in which the third, horizontal part of the duodenum is compressed in the
  narrowed space between the abdominal aorta and vertebral column posteriorly and
  the superior mesenteric artery anteriorly. Its mechanism is anatomic and
  biomechanical rather than Mendelian: the retroperitoneal/mesenteric fat pad that
  normally cushions the SMA and holds it away from the aorta is depleted by
  catabolic weight loss (or the aortomesenteric geometry is distorted by corrective
  spinal surgery, body casting, or rapid linear growth), narrowing the
  aortomesenteric angle and distance until the duodenum is trapped. The resulting
  obstruction causes postprandial pain, nausea, and vomiting, which reduce oral
  intake and drive further weight loss and further fat-pad depletion - a
  self-amplifying vicious cycle that is the defining pathophysiologic feature of
  the disorder and the reason nutritional restoration, not symptom suppression, is
  the therapeutic target.
disease_term:
  preferred_term: superior mesenteric artery syndrome
  term:
    id: MONDO:0002687
    label: superior mesenteric artery syndrome
synonyms:
- Wilkie syndrome
- Cast syndrome
- Arteriomesenteric duodenal compression syndrome
- Vascular compression of the duodenum
- Chronic duodenal obstruction
- Aorto-mesenteric compass syndrome
parents:
- Duodenal Obstruction

classifications:
  harrisons_chapter:
  - classification_value: GASTROINTESTINAL
    evidence:
    - reference: PMID:30291587
      reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Superior mesenteric artery syndrome (SMAS) is a rare cause of duodenal obstruction, resulting from the compression of the duodenum between superior mesenteric artery and aorta."
      explanation: >
        SMA syndrome is a mechanical duodenal obstruction and is managed as a
        gastrointestinal disorder, notwithstanding that the compressing structure is
        an artery.
progression:
- phase: Intermittent postprandial symptoms
  notes: >
    Early phase. Compression is partial and posture-dependent; symptoms occur after
    larger or solid meals and remit between them. Weight is often still preserved.
- phase: Established obstruction with reduced intake and weight loss
  notes: >
    The vicious cycle is engaged. Solids are avoided, then meals generally; weight
    and the aortomesenteric fat pad fall together, progressively narrowing the angle.
- phase: Severe nutritional and metabolic compromise or complications
  notes: >
    Marked undernutrition, dehydration, and hypochloraemic metabolic alkalosis, with
    risk of aspiration pneumonia, acute gastric dilatation and perforation, and
    obstructive pancreatitis. This is the phase that carries mortality.
- phase: Recovery after fat-pad restoration or surgical bypass
  notes: >
    Conservative management succeeds in roughly 70-80% of cases; laparoscopic
    duodenojejunostomy achieves 80-100% success when it fails. The course may remit
    with weight restoration, recur if weight is lost again, or remain chronic if
    obstruction and nutritional depletion continue to perpetuate one another.
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The initial treatment is usually conservative, including postural change, gastroduodenal decompression, and nutrient management (success rates: 70%-80%). If conservative therapy fails, surgical treatment (i.e., laparoscopic duodenojejunostomy) is recommended (success rates: 80%-100%)."
    explanation: >
      Quantifies recovery rates for the conservative and surgical routes out of the
      obstructed state.

mechanistic_hypotheses:
- hypothesis_group_id: fat_pad_depletion_vicious_cycle
  hypothesis_label: Self-amplifying fat-pad-depletion cycle
  status: CANONICAL
  description: >
    The canonical model of SMA syndrome is not a simple linear cascade but a
    positive-feedback loop. Depletion of the aortomesenteric fat pad narrows the
    aortomesenteric angle and compresses the duodenum; the resulting meal-provoked
    pain, nausea, and vomiting reduce oral intake; the reduced intake produces
    further weight loss and further fat-pad depletion, which narrows the angle
    still further. Edges tagged with this hypothesis group form the closed cycle
    (fat-pad depletion -> angle narrowing -> duodenal compression -> obstruction ->
    reduced intake -> weight loss -> fat-pad depletion). The clinical corollary is
    that the loop can only be broken by restoring the fat pad (nutritional
    rehabilitation, ideally delivered distal to the obstruction) or by surgically
    bypassing the compressed segment.
  evidence:
  - reference: PMID:31998513
    reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms that patients experience lead to further decreases in oral intake, which in turn brings about further weight and fat pad loss and thus worsening of the duodenal obstruction."
    explanation: >
      States the positive-feedback structure explicitly - symptoms reduce intake,
      which worsens fat-pad loss, which worsens the obstruction.

pathophysiology:
- name: Precipitating Catabolic Weight Loss or Anatomic Alteration
  biological_scale: ORGANISM
  description: >
    The upstream trigger. Two mechanistically distinct routes converge on the same
    aortomesenteric geometry. (1) A catabolic/undernutrition state producing rapid
    or substantial weight loss - anorexia nervosa and other restrictive eating,
    malignancy and cachexia, major burns, trauma, malabsorption, chronic infection,
    prolonged immobilisation, or severe systemic illness. (2) A change in the
    spatial relationship among the spine, aorta, SMA, and duodenum without primary
    fat loss - corrective spinal surgery for scoliosis (the classic paediatric
    setting), body casting (the origin of the name "cast syndrome"), rapid linear
    growth, or abdominal/retroperitoneal operations that alter intestinal fixation
    and tension. A third, less common route is constitutional: a congenital
    anatomic variant of the SMA origin (an abnormally low, caudally angled take-off)
    or of duodenal fixation (a short, high-inserting ligament of Treitz suspending
    the duodenum within the aortomesenteric window) can narrow the window from
    birth, so that a much smaller degree of fat loss is sufficient to precipitate
    obstruction.
  triggers:
  - preferred_term: Rapid or substantial weight loss
  - preferred_term: Corrective spinal surgery for scoliosis
  - preferred_term: Body casting or spinal traction
  - preferred_term: Congenital anatomic variant of SMA origin or duodenal fixation
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Frequently, predisposing medical conditions associated with catabolic states or rapid weight loss result in a decrease of the aortomesenteric angle and subsequent duodenal obstruction. External cast compression, anatomic variants and surgical alteration of the anatomy following spine surgery or ileoanal pouch anastomosis can also precipitate the syndrome."
    explanation: >
      Names all three arms of the trigger node - catabolic/weight-loss states,
      mechanical/surgical alteration of the anatomy, and anatomic variants - and
      links them to the narrowed aortomesenteric angle.
  - reference: PMID:29204239
    reference_title: "Wilkie's syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This syndrome can be congenital or acquired. The acquired type is more common and is generally caused by reduced perivascular fat surrounding the abdominal aorta and the superior mesenteric artery"
    explanation: >
      Establishes the congenital/constitutional arm as a distinct (if less common)
      route alongside the acquired, fat-loss-driven form.
  downstream:
  - target: Mesenteric Fat Pad Depletion
    causal_link_type: DIRECT
    description: >
      Catabolic weight loss mobilises the visceral adipose stores that constitute
      the aortomesenteric cushion.
  - target: Aortomesenteric Angle and Distance Narrowing
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Altered spinal and mesenteric geometry after deformity correction (lengthening and extension of the corrected spine, cranial displacement of the SMA origin, increased mesenteric tension), which narrows the aortomesenteric window without primary fat-pad depletion and so bypasses the adipose node.
    evidence:
    - reference: PMID:33905850
      reference_title: "Superior Mesenteric Artery Syndrome Following Scoliosis Surgery: A Systematic Review of Case Reports."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Superior mesenteric artery (SMA) syndrome is a well-recognized, rare complication of undergoing surgical correction of a spinal deformity."
      explanation: >
        Establishes the spinal-correction arm as a recognised route to SMA syndrome
        independent of primary catabolic weight loss.

- name: Mesenteric Fat Pad Depletion
  biological_scale: TISSUE
  description: >
    Loss of the retroperitoneal and mesenteric adipose cushion that surrounds the
    origin of the superior mesenteric artery. In health this fat pad splays the SMA
    away from the aorta and provides the space through which the third part of the
    duodenum passes. Its depletion by lipolysis during negative energy balance is
    the proximate anatomic lesion of the weight-loss arm of the disease, and its
    reconstitution is the therapeutic goal of conservative management.
  cell_types:
  - preferred_term: Visceral (mesenteric) white adipocyte
    term:
      id: CL:0000448
      label: white adipocyte
  biological_processes:
  - preferred_term: Triglyceride mobilization from the mesenteric fat depot
    term:
      id: GO:0006642
      label: triglyceride mobilization
    modifier: INCREASED
  locations:
  - preferred_term: Aortomesenteric (retroperitoneal) fat pad
    term:
      id: UBERON:0015143
      label: mesenteric fat pad
  - preferred_term: Visceral abdominal adipose tissue
    term:
      id: UBERON:0014454
      label: visceral abdominal adipose tissue
  evidence:
  - reference: PMID:31998513
    reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mesentery around the SMA is surrounded by a fatty tissue pad which forms a cushion that allows the duodenum to pass unobstructed between the SMA and the aorta."
    explanation: >
      Describes the normal function of the fat pad whose depletion defines this
      pathophysiology node.
  downstream:
  - target: Aortomesenteric Angle and Distance Narrowing
    causal_link_type: DIRECT
    hypothesis_groups:
    - fat_pad_depletion_vicious_cycle
    evidence:
    - reference: PMID:31998513
      reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Weight loss and its resulting malnutrition lead to a loss of said fat pad surrounding the SMA, which allows for migration of the SMA medially, thus resulting in a narrowing of the normal angle between the SMA and the aorta."
      explanation: >
        Directly asserts the causal step from fat-pad loss to medial migration of
        the SMA and narrowing of the aortomesenteric angle.

- name: Aortomesenteric Angle and Distance Narrowing
  biological_scale: TISSUE
  description: >
    Reduction of the angle at which the SMA leaves the abdominal aorta, and of the
    aorta-to-SMA distance at the level of the duodenum. Normative values vary by
    population; one cross-sectional series reported a mean angle of 54.07 +/- 8.53
    degrees and a mean distance of 16.25 +/- 3.44 mm. The operational diagnostic
    thresholds used in the largest prospective surgical series are an
    aortomesenteric angle of 22 degrees or less and/or a distance of 8 mm or less.
    This is a geometric, not a biochemical, lesion: no vascular occlusion,
    thrombosis, dissection, or ischaemia is involved, and the SMA itself is
    structurally normal.
  locations:
  - preferred_term: Superior mesenteric artery
    term:
      id: UBERON:0001182
      label: superior mesenteric artery
  - preferred_term: Abdominal aorta
    term:
      id: UBERON:0001516
      label: abdominal aorta
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis was achieved through barium swallow, CT/MR angiography (aortomesenteric angle ≤ 22°, distance ≤ 8 mm), endoscopy."
    explanation: >
      Gives the operational angle and distance thresholds used to define the
      narrowed aortomesenteric geometry in a prospective 39-patient cohort.
  - reference: PMID:38694377
    reference_title: "Evaluating aortomesenteric parameters in a tertiary center of Nepal for superior mesenteric artery syndrome diagnosis and risk factors: cross-sectional study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The study reveals a mean AMA of 54.07°±8.53° and a mean distance of 16.25±3.44 mm. Elevated BMI is found to positively correlate with AMA and distance, indicating that higher BMI values may augment these parameters"
    explanation: >
      Provides normative aortomesenteric angle/distance values and demonstrates the
      quantitative dependence of both parameters on BMI, the population-level
      counterpart of the fat-pad-depletion mechanism.
  notes: >
    An angle of 22 degrees or less and a distance of 8 mm or less are supportive
    operational cut-offs in the cited prospective cohort, but narrowed geometry can
    be present in asymptomatic individuals. Diagnosis therefore requires
    clinical-radiological concordance rather than a threshold alone.
  downstream:
  - target: Extrinsic Compression of the Third Part of the Duodenum
    causal_link_type: DIRECT
    hypothesis_groups:
    - fat_pad_depletion_vicious_cycle
    evidence:
    - reference: PMID:31998513
      reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This narrowing results in external mechanical compression of the duodenum as it passes between the SMA and the aorta."
      explanation: >
        States the causal step from the narrowed angle to mechanical compression of
        the duodenum.

- name: Extrinsic Compression of the Third Part of the Duodenum
  biological_scale: TISSUE
  description: >
    The primary lesion. The horizontal (third) portion of the duodenum, which
    crosses the midline in the aortomesenteric window, is squeezed between the SMA
    anteriorly and the aorta and vertebral column posteriorly. The compression is
    extrinsic - the duodenal wall and lumen are intrinsically normal - which is why
    endoscopy alone cannot establish the diagnosis and why bypassing or
    decompressing the segment relieves it.
  locations:
  - preferred_term: Third (horizontal) part of the duodenum
    term:
      id: UBERON:0002114
      label: duodenum
  evidence:
  - reference: PMID:31998513
    reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is defined as the extrinsic compression of the third part of the duodenum by the aorta posteriorly and the superior mesenteric artery anteriorly."
    explanation: >
      Defines the primary anatomic lesion, including the anterior and posterior
      compressing structures.
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The syndrome is caused by compression of the third part of the duodenum in the angle between the aorta and the superior mesenteric artery."
    explanation: >
      Independent review confirming the site and mechanism of compression.
  downstream:
  - target: Proximal Duodenal Obstruction and Gastroduodenal Stasis
    causal_link_type: DIRECT
    hypothesis_groups:
    - fat_pad_depletion_vicious_cycle

- name: Proximal Duodenal Obstruction and Gastroduodenal Stasis
  biological_scale: ORGANISM
  description: >
    Partial or complete high intestinal obstruction at the third part of the
    duodenum. Chyme cannot pass the compressed segment, so the proximal duodenum
    and stomach dilate and empty slowly. Obstruction may be intermittent and
    posture-dependent - supine positioning worsens it and left lateral decubitus,
    prone, or knee-chest positions can transiently relieve it - which explains both
    the fluctuating symptoms and the positional manoeuvres used in conservative
    management.
  locations:
  - preferred_term: Duodenum
    term:
      id: UBERON:0002114
      label: duodenum
  - preferred_term: Stomach
    term:
      id: UBERON:0000945
      label: stomach
  biological_processes:
  - preferred_term: Gastroduodenal emptying
    term:
      id: GO:0035483
      label: gastric emptying
    modifier: DECREASED
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Barium swallow showed a gastroduodenal dilation in 57% of patients, and a delayed gastroduodenal emptying in 38%."
    explanation: >
      Quantifies proximal dilation and delayed emptying, the direct functional
      consequences of the compressed duodenal segment, in a prospective cohort.
  downstream:
  - target: Meal-Provoked Symptoms and Reduced Oral Intake
    causal_link_type: DIRECT
    hypothesis_groups:
    - fat_pad_depletion_vicious_cycle

- name: Meal-Provoked Symptoms and Reduced Oral Intake
  biological_scale: ORGANISM
  description: >
    Eating loads the obstructed segment, producing postprandial epigastric pain,
    nausea, early satiety, bloating, and vomiting that begins within roughly
    15-20 minutes of a meal and is characteristically relieved by emesis. Patients
    learn to avoid solids, then to avoid eating, so the obstruction is converted
    into a behavioural restriction of intake. This is the node at which a
    mechanical lesion becomes a nutritional one, and it is the hinge of the vicious
    cycle.
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms are variable, consisting of postprandial abdominal pain, nausea and vomiting, early satiety, anorexia, and weight loss and can mimic anorexia nervosa or functional dyspepsia."
    explanation: >
      Lists the meal-provoked symptom cluster and notes that it can be mistaken for
      a primary eating disorder, which is why intake falls.
  downstream:
  - target: Progressive Weight Loss and Malnutrition
    causal_link_type: DIRECT
    hypothesis_groups:
    - fat_pad_depletion_vicious_cycle
  - target: Obstructive and Aspiration Complications
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Recurrent vomiting against a dilated, obstructed proximal gut, producing aspiration of gastric contents and hypochloraemic metabolic alkalosis.
    - Progressive acute gastric distension, which can advance to mural ischaemia, necrosis, and perforation.

- name: Progressive Weight Loss and Malnutrition
  biological_scale: ORGANISM
  description: >
    Sustained negative energy balance with falling BMI, dehydration, and
    electrolyte and acid-base disturbance (classically hypochloraemic metabolic
    alkalosis from recurrent vomiting). In the largest prospective series the
    median BMI at presentation was 17.8 kg/m2, and surgical relief of the
    obstruction raised it significantly - consistent with the undernutrition being
    substantially driven by the obstruction rather than merely preceding it, though
    that series was single-arm and uncontrolled with concurrent nutritional care.
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty-nine patients (11 M/28 F, median age 38 years, median BMI 17.8 kg/m2) were included."
    explanation: >
      Documents the low BMI characteristic of the malnutrition node in a
      prospectively enrolled SMA syndrome cohort.
  downstream:
  - target: Mesenteric Fat Pad Depletion
    causal_link_type: DIRECT
    description: >
      The closing edge of the vicious cycle. Obstruction-driven weight loss further
      depletes the very fat pad whose loss caused the obstruction, so the
      aortomesenteric angle narrows further and the disease becomes self-sustaining
      unless nutrition is restored or the segment is bypassed.
    hypothesis_groups:
    - fat_pad_depletion_vicious_cycle
    evidence:
    - reference: PMID:31998513
      reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The symptoms that patients experience lead to further decreases in oral intake, which in turn brings about further weight and fat pad loss and thus worsening of the duodenal obstruction."
      explanation: >
        Explicitly closes the loop: obstruction-driven symptoms cause further fat
        pad loss, which worsens the obstruction.

- name: Obstructive and Aspiration Complications
  biological_scale: ORGANISM
  description: >
    Uncommon but potentially fatal sequelae of unrelieved obstruction and recurrent
    vomiting: aspiration pneumonia, respiratory depression from metabolic
    alkalosis, acute gastric dilatation progressing to necrosis and perforation,
    peptic ulceration, and obstructive acute pancreatitis. These complications are
    the reason delayed diagnosis carries meaningful mortality.
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Because recurrent vomiting leads to aspiration pneumonia or respiratory depression via metabolic alkalosis, early diagnosis is required."
    explanation: >
      Names the aspiration and metabolic-alkalosis complications and the diagnostic
      urgency they create.

phenotypes:
- category: Gastrointestinal
  name: Postprandial Epigastric Pain
  description: >
    Upper abdominal/epigastric pain beginning shortly after eating, characteristically
    relieved by vomiting or by lying in a left lateral decubitus, prone, or knee-chest
    position.
  phenotype_term:
    preferred_term: Postprandial epigastric pain
    term:
      id: HP:0410019
      label: Epigastric pain
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Superior mesenteric artery syndrome is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, anorexia and weight loss."
    explanation: >
      Names postprandial epigastric pain as a defining feature of the syndrome.

- category: Gastrointestinal
  name: Nausea
  phenotype_term:
    preferred_term: Nausea
    term:
      id: HP:0002018
      label: Nausea
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Superior mesenteric artery syndrome is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, anorexia and weight loss."
    explanation: Nausea is listed among the characterising symptoms.

- category: Gastrointestinal
  name: Vomiting
  description: >
    Recurrent, often bilious vomiting after meals. Emesis characteristically relieves
    the pain, and its recurrence drives dehydration, electrolyte loss, and aspiration
    risk.
  phenotype_term:
    preferred_term: Postprandial bilious vomiting
    term:
      id: HP:0002013
      label: Vomiting
  evidence:
  - reference: PMID:23959808
    reference_title: "Superior mesenteric artery syndrome and its associated gastrointestinal implications."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Common symptoms associated with this syndrome include intermittent postprandial abdominal pain, nausea, and bilious vomiting."
    explanation: >
      Identifies the vomiting as postprandial and bilious, consistent with an
      obstruction distal to the ampulla.

- category: Gastrointestinal
  name: Early Satiety
  phenotype_term:
    preferred_term: Early satiety
    term:
      id: HP:0033842
      label: Early satiety
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms are variable, consisting of postprandial abdominal pain, nausea and vomiting, early satiety, anorexia, and weight loss and can mimic anorexia nervosa or functional dyspepsia."
    explanation: Early satiety is listed in the core symptom cluster.

- category: Gastrointestinal
  name: Anorexia
  description: >
    Loss of appetite and food aversion. In SMA syndrome this is largely a learned
    consequence of meal-provoked pain rather than a primary psychiatric
    disturbance, though the two can coexist and are easily conflated.
  phenotype_term:
    preferred_term: Loss of appetite
    term:
      id: HP:0002039
      label: Anorexia
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Superior mesenteric artery syndrome is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, anorexia and weight loss."
    explanation: Anorexia is listed among the characterising symptoms.

- category: Gastrointestinal
  name: High Intestinal Obstruction
  description: >
    Partial or complete obstruction at the third part of the duodenum, the
    defining functional abnormality of the syndrome.
  diagnostic: true
  phenotype_term:
    preferred_term: Duodenal (high intestinal) obstruction
    term:
      id: HP:0005250
      label: High intestinal obstruction
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Superior mesenteric artery syndrome (SMAS) is a rare cause of duodenal obstruction, resulting from the compression of the duodenum between superior mesenteric artery and aorta."
    explanation: >
      Establishes duodenal obstruction as the defining clinical abnormality of the
      disease.

- category: Nutritional
  name: Weight Loss
  description: >
    Weight loss is both the commonest precipitant of SMA syndrome and one of its
    consequences - the dual role that generates the vicious cycle.
  phenotype_term:
    preferred_term: Weight loss
    term:
      id: HP:0001824
      label: Weight loss
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Superior mesenteric artery syndrome is uncommon and characterized by postprandial epigastric pain, nausea, vomiting, anorexia and weight loss."
    explanation: Weight loss is listed among the characterising features.

- category: Nutritional
  name: Low Body Mass Index
  description: >
    Patients are characteristically underweight at presentation; low BMI together
    with chronic refractory upper digestive symptoms is the classic trigger for
    suspecting the diagnosis. Median BMI in the largest prospective surgical series
    was 17.8 kg/m2.
  phenotype_term:
    preferred_term: Decreased body mass index
    term:
      id: HP:0045082
      label: Decreased body mass index
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SMAS is a rare condition that should be suspected in cases of chronic, refractory upper digestive symptoms, particularly in females with low BMIs."
    explanation: >
      Identifies low BMI as a characteristic feature of the affected population.

- category: Nutritional
  name: Malnutrition
  phenotype_term:
    preferred_term: Malnutrition
    term:
      id: HP:0004395
      label: Malnutrition
  evidence:
  - reference: PMID:31998513
    reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Superior mesenteric artery (SMA) syndrome is a rare complication of severe malnutrition that leads to intestinal obstruction"
    explanation: >
      Links severe malnutrition directly to the obstruction, supporting malnutrition
      as an integral clinical feature.

- category: Respiratory
  name: Aspiration Pneumonia
  description: >
    A serious complication of recurrent vomiting against a distended, obstructed
    proximal gut.
  phenotype_term:
    preferred_term: Aspiration pneumonia
    term:
      id: HP:0011951
      label: Aspiration pneumonia
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Because recurrent vomiting leads to aspiration pneumonia or respiratory depression via metabolic alkalosis, early diagnosis is required."
    explanation: >
      Directly identifies aspiration pneumonia as a consequence of the recurrent
      vomiting caused by the obstruction.

- category: Metabolic
  name: Hypochloremic Metabolic Alkalosis
  description: >
    Loss of gastric hydrochloric acid through recurrent vomiting produces a
    hypochloraemic, hypokalaemic metabolic alkalosis, which in severe cases causes
    compensatory hypoventilation and respiratory depression.
  phenotype_term:
    preferred_term: Hypochloremic metabolic alkalosis
    term:
      id: HP:0005977
      label: Hypochloremic metabolic alkalosis
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Because recurrent vomiting leads to aspiration pneumonia or respiratory depression via metabolic alkalosis, early diagnosis is required."
    explanation: >
      Identifies vomiting-induced metabolic alkalosis, and the respiratory depression
      it causes, as a recognised consequence of the obstruction.

- category: Gastrointestinal
  name: Gastric Perforation
  description: >
    Acute gastric dilatation proximal to the obstruction can progress to mural
    ischaemia, necrosis, and perforation - a rare but potentially fatal complication.
  phenotype_term:
    preferred_term: Gastric perforation
    term:
      id: HP:6000383
      label: Gastric perforation
  evidence:
  - reference: PMID:31998513
    reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "they can show complications of this syndrome, such as acute gastric dilatation."
    explanation: >
      Documents acute gastric dilatation as a recognised complication. The
      progression from dilatation to perforation is not asserted by this source, so
      support is recorded as PARTIAL.

- category: Gastrointestinal
  name: Acute Pancreatitis
  description: >
    Obstructive acute pancreatitis is an uncommon complication, attributed to
    duodenal distension and impaired pancreatic outflow at the aortomesenteric
    compression.
  phenotype_term:
    preferred_term: Acute pancreatitis
    term:
      id: HP:0001735
      label: Acute pancreatitis
  notes: >
    Reported in the SMA syndrome complication literature and surfaced by the Edison
    deep-research report, but no PMID with a quotable abstract sentence linking
    acute pancreatitis to SMA syndrome was located, so no evidence item is asserted.
    Retained as a described but unevidenced complication rather than dropped.

imaging_findings:
- name: Reduced Aortomesenteric Angle on CT Angiography
  modality: CT
  description: >
    Sagittal reconstruction of contrast-enhanced abdominal CT (or CT/MR angiography)
    measures the angle at which the SMA leaves the aorta. Values of 22 degrees or
    less, together with an aortomesenteric distance of 8 mm or less, are the
    operational diagnostic criteria used in the largest prospective series, in
    which the median measured angle was 11 degrees and the median distance 5 mm.
    A narrowed angle in the absence of demonstrated duodenal obstruction is not
    diagnostic.
  diagnostic: true
  located_in:
    preferred_term: Superior mesenteric artery
    term:
      id: UBERON:0001182
      label: superior mesenteric artery
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Median aortomesenteric angle was 11° and distance was 5 mm."
    explanation: >
      Reports the measured aortomesenteric geometry in a prospectively enrolled
      SMA syndrome cohort, quantifying the imaging finding.
  - reference: PMID:31127323
    reference_title: "Superior mesenteric artery syndrome: a radiographic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Imaging can assist in diagnosis by demonstrating characteristic findings of reduced aortomesenteric angle, reduced aortomesenteric distance, gastroduodenal distention, bowel caliber narrowing at the takeoff of the superior mesenteric artery from the aorta, as well as delayed gastric emptying or positional obstruction observed with real time with fluoroscopy."
    explanation: >
      Enumerates the characteristic imaging findings, including the reduced angle
      and distance and the caliber change at the SMA takeoff.

- name: Gastroduodenal Distention with Abrupt Caliber Change at the SMA Crossing
  modality: OTHER
  description: >
    On an upper gastrointestinal barium series the stomach and proximal duodenum
    are dilated with abrupt hold-up of contrast at the level where the SMA crosses
    the third part of the duodenum, and gastroduodenal emptying is delayed.
    Obstruction may be positional, improving in the prone or left lateral decubitus
    position under real-time fluoroscopy.
  notes: >
    Modality is recorded as OTHER because a barium/upper-GI series is fluoroscopic
    rather than plain-film projectional radiography, and ImagingModalityEnum has no
    FLUOROSCOPY value.
  located_in:
    preferred_term: Duodenum
    term:
      id: UBERON:0002114
      label: duodenum
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Barium swallow showed a gastroduodenal dilation in 57% of patients, and a delayed gastroduodenal emptying in 38%."
    explanation: >
      Quantifies gastroduodenal dilation and delayed emptying on barium swallow in a
      prospective cohort.

environmental:
- name: Rapid or Substantial Weight Loss
  description: >
    Any catabolic or undernutrition state producing rapid loss of visceral fat -
    anorexia nervosa and other restrictive eating disorders, malignancy and
    cachexia, burns, trauma, malabsorption, chronic infection, and prolonged
    severe illness. This is the commonest precipitant.
  influences_mechanisms:
  - target: Precipitating Catabolic Weight Loss or Anatomic Alteration
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Catabolic or undernutrition states directly establish the weight-loss arm of
      the precipitating mechanism.
    evidence:
    - reference: PMID:31998513
      reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "SMA syndrome can be the result of a multitude of medical conditions that lead to weight loss and a malnourished state, namely wasting diseases such as cancer, burns, AIDS, and chronic infections; malabsorptive states; or voluntary or involuntary lack of caloric intake such as patients with anorexia nervosa (AN)."
      explanation: >-
        Directly links catabolic and undernutrition conditions to the weight-loss
        state that precipitates SMA syndrome.
  evidence:
  - reference: PMID:31998513
    reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SMA syndrome can be the result of a multitude of medical conditions that lead to weight loss and a malnourished state, namely wasting diseases such as cancer, burns, AIDS, and chronic infections; malabsorptive states; or voluntary or involuntary lack of caloric intake such as patients with anorexia nervosa (AN)."
    explanation: >
      Enumerates the weight-loss states that precipitate SMA syndrome.

- name: Corrective Spinal Surgery for Scoliosis
  exposure_term:
    preferred_term: surgical procedure exposure
    term:
      id: ECTO:2000054
      label: exposure to surgery
  description: >
    Surgical correction of a spinal deformity is a well-recognised precipitant,
    particularly in adolescents with adolescent idiopathic scoliosis and a low
    preoperative BMI. Reported latency to symptom onset diverges markedly between
    the two pooled systematic reviews - a mean of 9.6 +/- 9.5 days in one and a mean
    of 69 days (range 3 days to 4 years) in the other - so onset can be anywhere
    from the first postoperative days to years later, and a late presentation does
    not exclude the diagnosis.
  influences_mechanisms:
  - target: Precipitating Catabolic Weight Loss or Anatomic Alteration
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Corrective spine surgery directly supplies the anatomic-alteration arm of the
      precipitating mechanism, which then narrows the aortomesenteric geometry
      without requiring primary fat-pad depletion.
    evidence:
    - reference: PMID:17476104
      reference_title: "Recalling superior mesenteric artery syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "External cast compression, anatomic variants and surgical alteration of the anatomy following spine surgery or ileoanal pouch anastomosis can also precipitate the syndrome."
      explanation: >-
        Explicitly identifies surgical alteration after spine surgery as a
        precipitating route to SMA syndrome.
  evidence:
  - reference: PMID:39118170
    reference_title: "Superior mesenteric artery syndrome following spine surgery in idiopathic adolescent scoliosis: a systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Superior mesenteric artery syndrome (SMAS) is a rare and unpredictable complication after correction spine surgery for adolescent idiopathic scoliosis (AIS)."
    explanation: >
      Establishes corrective spine surgery for adolescent idiopathic scoliosis as a
      recognised precipitating exposure.
  - reference: PMID:39118170
    reference_title: "Superior mesenteric artery syndrome following spine surgery in idiopathic adolescent scoliosis: a systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean interval between spine surgery and symptoms of SAMS was 69 days, with high between-studies variability (3 days to 4 years)."
    explanation: >
      Gives the longer latency estimate that diverges from the 9.6-day mean of the
      other pooled review, documenting the wide and uncertain time-to-onset window.
  - reference: PMID:33905850
    reference_title: "Superior Mesenteric Artery Syndrome Following Scoliosis Surgery: A Systematic Review of Case Reports."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean age of patients with SMA syndrome following scoliosis surgery was 14.7 ± 2.9 years and the majority (n = 42, 80.8%) were girls. The most frequently reported scoliosis type was adolescent idiopathic scoliosis (n = 34, 65.4%). The mean postoperative days (POD) (interval between the surgical treatment and the onset of symptoms) was 9.6 ± 9.5 days."
    explanation: >
      Quantifies the demographics and post-operative latency of the
      scoliosis-surgery arm across 52 pooled cases.

- name: Body Casting and External Spinal Compression
  description: >
    Application of a body cast or spinal traction for scoliosis - the origin of the
    historical name "cast syndrome" - can precipitate the same duodenal compression
    without primary fat loss.
  influences_mechanisms:
  - target: Precipitating Catabolic Weight Loss or Anatomic Alteration
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      External cast compression directly supplies the mechanical-alteration arm of
      the precipitating mechanism.
    evidence:
    - reference: PMID:17476104
      reference_title: "Recalling superior mesenteric artery syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "External cast compression, anatomic variants and surgical alteration of the anatomy following spine surgery or ileoanal pouch anastomosis can also precipitate the syndrome."
      explanation: >-
        Explicitly identifies external cast compression as a precipitant of SMA
        syndrome.
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "External cast compression, anatomic variants and surgical alteration of the anatomy following spine surgery or ileoanal pouch anastomosis can also precipitate the syndrome."
    explanation: >
      Names external cast compression and anatomic/surgical alteration as
      precipitants distinct from weight loss.

prevalence:
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: RARE
  notes: >
    Estimated at 0.013%-3% of the general population from historical barium studies;
    the wide range reflects radiographic ascertainment in selected populations rather
    than a population registry, so no precise numeric rate is asserted here.
  evidence:
  - reference: PMID:31998513
    reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The overall prevalence of SMA syndrome is unknown; however, it is estimated to be 0.013%"
    explanation: >
      Source states the prevalence is unknown and gives only a wide
      barium-study-derived estimate, supporting a qualitative RARE class rather than
      a numeric rate.

epidemiology:
- name: Demographics
  description: >
    Median age at presentation around 23 years (reported range 0-91 years), with a
    female predominance of roughly 3:2 and a peak in adolescents and young adults.
    In the scoliosis-surgery subgroup the mean age is about 15 years and over 80%
    of reported cases are girls.
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The median age of patients is 23 years old (range 0-91 years old) and predominant in females over males with a ratio of 3:2."
    explanation: Gives the age distribution and sex ratio.
  - reference: PMID:33905850
    reference_title: "Superior Mesenteric Artery Syndrome Following Scoliosis Surgery: A Systematic Review of Case Reports."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean age of patients with SMA syndrome following scoliosis surgery was 14.7 ± 2.9 years and the majority (n = 42, 80.8%) were girls."
    explanation: >
      Supplies the age and sex distribution of the scoliosis-surgery subgroup quoted
      in this epidemiology entry.

treatments:
- name: Nutritional Rehabilitation and Weight Restoration
  description: >
    First-line and mechanistically definitive therapy. The goal is to restore the
    aortomesenteric fat pad, which widens the angle and relieves the compression -
    not merely to suppress nausea. Delivered as small, frequent, energy-dense
    liquid or soft feeds when oral intake is tolerated, with careful electrolyte
    monitoring for refeeding syndrome. Conservative management succeeds in roughly
    70-80% of cases.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: nutritional support
    term:
      id: NCIT:C15433
      label: Nutritional Support
  target_mechanisms:
  - target: Mesenteric Fat Pad Depletion
    treatment_effect: RESTORES
    description: >
      Weight restoration reconstitutes the aortomesenteric fat pad, reversing the
      upstream anatomic lesion and breaking the vicious cycle at its origin.
    evidence:
    - reference: PMID:31998513
      reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Treatment of SMA syndrome necessitates gaining enough weight to ultimately reconstitute the fat pad between the aorta and the SMA"
      explanation: >
        States that the therapeutic mechanism is reconstitution of the fat pad, i.e.
        reversal of the Mesenteric Fat Pad Depletion node.
    - reference: PMID:29204239
      reference_title: "Wilkie's syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "After diagnosis, the patient followed a high-calorie diet, and 2 months later an ultrasound scan proved the restoration of the aorto-mesenteric angle as a consequence of increased perivascular fat with regression of symptoms."
      explanation: >
        Direct in-vivo demonstration of the treatment mechanism - refeeding restored
        the perivascular fat, which restored the aortomesenteric angle, which
        resolved the symptoms - closing the causal loop in the therapeutic direction.
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The initial treatment is usually conservative, including postural change, gastroduodenal decompression, and nutrient management (success rates: 70%-80%)."
    explanation: >
      Establishes conservative nutritional/decompressive management as first line and
      quantifies its success rate.

- name: Post-Pyloric (Nasojejunal) Enteral Feeding
  description: >
    Enteral nutrition delivered by a tube whose tip lies distal to the compressed
    third part of the duodenum. This bypasses the obstruction so that calories can be
    delivered despite it, allowing weight gain and fat-pad reconstitution - an
    intervention that exploits the fact that the bowel distal to the compression is
    entirely normal.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: enteral tube feeding
    term:
      id: NCIT:C93322
      label: Enteral Tube Feeding
  target_mechanisms:
  - target: Proximal Duodenal Obstruction and Gastroduodenal Stasis
    treatment_effect: BYPASSES
    description: >
      Feeding distal to the compressed segment circumvents the obstruction rather
      than relieving the compression itself.
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "first-line treatment is usually conservative with jejunal or parenteral nutrition for restoration of the aortomesenteric fatty tissue."
    explanation: >
      Identifies jejunal (post-pyloric) feeding as first-line conservative therapy
      aimed specifically at restoring the aortomesenteric fat.

- name: Total Parenteral Nutrition
  description: >
    Used when enteral feeding distal to the obstruction is impossible or
    insufficient, or when the obstruction is complete. Provides calories for weight
    restoration entirely independently of the gut.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: total parenteral nutrition
    term:
      id: NCIT:C29484
      label: Total Parenteral Nutrition
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "first-line treatment is usually conservative with jejunal or parenteral nutrition for restoration of the aortomesenteric fatty tissue."
    explanation: >
      Names parenteral nutrition alongside jejunal feeding as conservative therapy
      aimed at restoring the aortomesenteric fat pad.

- name: Nasogastric Decompression
  description: >
    Gastroduodenal decompression relieves acute distension, reduces vomiting and
    aspiration risk, and allows correction of fluid and electrolyte deficits during
    the acute presentation. Symptomatic rather than mechanism-reversing.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: nasogastric decompression
    term:
      id: NCIT:C70910
      label: Nasogastric Decompression
  evidence:
  - reference: PMID:28356803
    reference_title: "Superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The SMAS was suspected and a nasogastric tube was inserted, stomach decompression and the correction of electrolytes disbalance were made."
    explanation: >
      Documents nasogastric decompression plus electrolyte correction as the acute
      management of post-scoliosis-surgery SMA syndrome.

- name: Laparoscopic Duodenojejunostomy
  description: >
    The best-supported definitive operation when conservative management fails. A
    side-to-side anastomosis between the duodenum proximal to the compression and
    the jejunum bypasses the aortomesenteric window entirely, so the obstruction is
    circumvented rather than the angle corrected. Reported success rates are
    80-100%; in a prospective 39-patient cohort symptom scores fell and BMI rose
    significantly at a median 47 months of follow-up.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: laparoscopic duodenojejunostomy
    term:
      id: NCIT:C15725
      label: Laparoscopic Surgery
  target_mechanisms:
  - target: Extrinsic Compression of the Third Part of the Duodenum
    treatment_effect: BYPASSES
    description: >
      Diverts chyme around the compressed duodenal segment without altering the
      aortomesenteric geometry.
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At a median follow-up of 47 months, the overall symptom score significantly dropped (10 vs. 32, p < 0.0001) and BMI increased (19.5 vs. 17.8, p < 0.0001)."
    explanation: >
      Quantifies symptom and BMI improvement after duodenojejunostomy in the largest
      prospective cohort.
  - reference: PMID:39191411
    reference_title: "Laparoscopic Surgery for Superior Mesenteric Artery Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All operations were successfully completed laparoscopically, and with a median follow-up of 65 months, the overall symptom score was significantly reduced from 32 to 8 (p < 0.0001) and the BMI was increased from 17.2 kg/m2 to 21.8 kg/m2 (p < 0.0001)."
    explanation: >
      Independent 66-patient laparoscopic series confirming durable symptom and BMI
      improvement.
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "If conservative therapy fails, surgical treatment (i.e., laparoscopic duodenojejunostomy) is recommended (success rates: 80%-100%)."
    explanation: >
      Positions laparoscopic duodenojejunostomy as the recommended operation after
      failed conservative therapy and gives its success rate.

- name: Strong Procedure (Division of the Ligament of Treitz)
  description: >
    Division of the ligament of Treitz with mobilisation of the duodenum allows the
    duodenum to drop caudally out of the narrowed aortomesenteric window. Unlike
    duodenojejunostomy this addresses the position of the duodenum relative to the
    compressing structures rather than bypassing the segment; it is anatomically
    distinct from duodenojejunostomy and less consistently effective.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Extrinsic Compression of the Third Part of the Duodenum
    treatment_effect: INHIBITS
    description: >
      Mobilising the duodenum out of the aortomesenteric window relieves the
      extrinsic compression directly.
  evidence:
  - reference: PMID:17476104
    reference_title: "Recalling superior mesenteric artery syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "If conservative management fails, surgical options include open or laparoscopic duodenojejunostomy or duodenal mobilization and division of the ligament of Treitz."
    explanation: >
      Names duodenal mobilisation with division of the ligament of Treitz as a
      surgical option distinct from duodenojejunostomy.

diagnosis:
- name: Clinical-Radiological Concordance
  description: >
    Diagnosis requires BOTH a compatible obstructive clinical picture AND imaging
    evidence of duodenal compression with narrowed aortomesenteric geometry. A
    narrow angle or distance in isolation occurs in asymptomatic individuals and is
    not diagnostic; conversely, endoscopy cannot establish an extrinsic compression.
    In practice barium swallow, contrast-enhanced CT or CT/MR angiography, and
    endoscopy are combined.
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis was achieved through barium swallow, CT/MR angiography (aortomesenteric angle ≤ 22°, distance ≤ 8 mm), endoscopy."
    explanation: >
      Describes the multimodal diagnostic pathway and the imaging thresholds applied.
  - reference: PMID:23959808
    reference_title: "Superior mesenteric artery syndrome and its associated gastrointestinal implications."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CT angiography is currently favored in the literature for diagnosis as it can not only show the narrowed aorto-mesenteric angle and distance, but also the extent of duodenal obstruction."
    explanation: >
      Explains why CT angiography is preferred - it captures both the geometry and
      the obstruction, i.e. both halves of the concordance requirement.

differential_diagnoses:
- name: Nutcracker Syndrome (Left Renal Vein Entrapment)
  description: >
    The other clinical consequence of a narrowed aortomesenteric angle. The same
    geometry that traps the duodenum also traps the left renal vein, so the two
    entities share an anatomic substrate, are frequently co-reported, and can
    coexist in the same patient. They are nonetheless distinct diseases with
    distinct compressed structures and distinct presentations, and must not be
    conflated.
  distinguishing_features:
  - Nutcracker syndrome compresses the LEFT RENAL VEIN and presents as a urologic/venous syndrome with haematuria, proteinuria, left flank pain, pelvic congestion, and left varicocele.
  - SMA syndrome compresses the THIRD PART OF THE DUODENUM and presents as a gastrointestinal obstructive syndrome with postprandial pain, vomiting, and weight loss.
  evidence:
  - reference: PMID:29204239
    reference_title: "Wilkie's syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The reduced angle compresses the structures situated between the aorta and the superior mesenteric artery, such as the duodenum and left renal vein; this can determine painful crises, intestinal subocclusions, and left varicocele."
    explanation: >
      Documents that the same narrowed aortomesenteric angle compresses both the
      duodenum and the left renal vein, establishing the shared substrate while
      distinguishing the two symptom complexes.

- name: Anorexia Nervosa
  description: >
    The most consequential differential. SMA syndrome mimics a restrictive eating
    disorder (food avoidance, low BMI, vomiting), AND anorexia nervosa is one of
    its commonest causes, so the two are bidirectionally confusable and frequently
    coexist. Attributing SMA-syndrome symptoms to the psychiatric diagnosis alone
    delays treatment and blocks weight restoration.
  distinguishing_features:
  - In SMA syndrome food avoidance is secondary to reproducible meal-provoked pain relieved by emesis or postural change, and imaging shows duodenal obstruction with a narrowed aortomesenteric angle.
  - In uncomplicated anorexia nervosa there is a primary drive for thinness and fear of weight gain, and imaging shows no duodenal obstruction.
  evidence:
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms are variable, consisting of postprandial abdominal pain, nausea and vomiting, early satiety, anorexia, and weight loss and can mimic anorexia nervosa or functional dyspepsia."
    explanation: >
      States explicitly that SMA syndrome can mimic anorexia nervosa.

- name: Functional Dyspepsia and Gastroparesis
  description: >
    Non-obstructive upper-gut motility and symptom disorders that produce
    overlapping postprandial pain, nausea, bloating, and early satiety. Gastroparesis
    frequently coexists with SMA syndrome in malnourished patients.
  distinguishing_features:
  - Neither produces a fixed extrinsic caliber change at the third part of the duodenum or a narrowed aortomesenteric angle on cross-sectional imaging.
  - Neither shows the abrupt positional relief (prone, knee-chest, left lateral decubitus) characteristic of SMA syndrome.
  evidence:
  - reference: PMID:31998513
    reference_title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Concurrent gastroparesis was diagnosed clinically in all eight patients."
    explanation: >
      Documents that gastroparesis coexisted in every case of a confirmed SMA
      syndrome series, supporting coexistence rather than mutual exclusion and
      explaining why the two are hard to disentangle clinically.
  - reference: PMID:37383896
    reference_title: "Superior mesenteric artery syndrome: Diagnosis and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms are variable, consisting of postprandial abdominal pain, nausea and vomiting, early satiety, anorexia, and weight loss and can mimic anorexia nervosa or functional dyspepsia."
    explanation: >
      Names functional dyspepsia as a condition SMA syndrome mimics.

clinical_trials:
- name: NCT03416647
  status: COMPLETED
  description: >
    Prospective single-institution registry of 39 consecutive SMA syndrome patients
    (2008-2016), all treated with duodenojejunostomy, with symptom score, BMI, and
    barium swallow reassessed at follow-up. Published as PMID:30291587.
  target_phenotypes:
  - preferred_term: Duodenal (high intestinal) obstruction
    term:
      id: HP:0005250
      label: High intestinal obstruction
  evidence:
  - reference: clinicaltrials:NCT03416647
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution"
    supports: SUPPORT
    snippet: "Between 2008 and 2016, 39 consecutive patients with chronic gastrointestinal symptoms and a diagnosis of SMAS were prospectively included in the study, in order to describe their demographic, clinical and outcome features. All patients underwent duodenojejunostomy."
    explanation: >
      Describes the prospective cohort and the uniform duodenojejunostomy
      intervention underpinning the surgical evidence base.

- name: NCT06970093
  status: RECRUITING
  description: >
    Randomised open-label comparison of one-anastomosis gastric bypass versus
    duodenojejunostomy for SMA syndrome, with 12-month symptom, nutritional, and
    quality-of-life endpoints. Addresses the near-absence of comparative surgical
    evidence.
  target_phenotypes:
  - preferred_term: Postprandial bilious vomiting
    term:
      id: HP:0002013
      label: Vomiting
  - preferred_term: Weight loss
    term:
      id: HP:0001824
      label: Weight loss
  evidence:
  - reference: clinicaltrials:NCT06970093
    reference_title: "One Anastomosis Gastric Bypass (OAGB) vs Duodeno-jejunostomy For Treatment of Superior Mesenteric Artery Syndrome: A Prospective Randomized Control Trial"
    supports: SUPPORT
    snippet: "This condition causes the duodenum to be squeezed between two arteries, leading to severe nausea, vomiting, and weight loss."
    explanation: >
      Confirms the trial targets the mechanical duodenal compression and its cardinal
      symptoms.

- name: NCT03937193
  status: COMPLETED
  description: >
    Completed 510-participant CT study establishing the normal range of
    aortomesenteric angle and distance in a young Chinese population and
    correlating both with retroperitoneal adipose tissue. Directly addresses the
    threshold-variability knowledge gap and provides population-level confirmation
    of the fat-pad mechanism.
  evidence:
  - reference: clinicaltrials:NCT03937193
    reference_title: "Normal Range of Superior Mesenteric Artery on Computerized Tomography in Young Chinese Population and Its Correlation With Retroperitoneal Adipose Tissue"
    supports: SUPPORT
    snippet: "In literature, superior mesenteric artery (SMA) angle, also named as aortomesenteric angle (AMA), varies greatly in both adult and children; while the aortomesenteric distance also ranges widely. Both AMA and AMD are influenced by retroperitoneal fat."
    explanation: >
      Documents both the wide variation in reported normal aortomesenteric geometry
      and its dependence on retroperitoneal fat.

- name: NCT04515251
  status: RECRUITING
  description: >
    Prospective multicentre observational study deriving normative ultrasound
    aortomesenteric measurements in healthy children aged 10-15 years, the age band
    in which post-scoliosis-surgery SMA syndrome peaks. Paediatric reference
    standards remain under development.
  evidence:
  - reference: clinicaltrials:NCT04515251
    reference_title: "A Prospective, Observational, Multicenter Study on Ultrasound Evaluation of Superior Mesenteric Artery Measurements in a Healthy Pediatric Population"
    supports: SUPPORT
    snippet: "Multicenter, prospective, observational research project on children aged from 10 to 15 years old undergoing abdominal ultrasound examinations during routine clinical practice."
    explanation: >
      Confirms the study is deriving paediatric normative aortomesenteric ultrasound
      values in the relevant age band.

- name: NCT07115472
  status: RECRUITING
  description: >
    Single-group study of fluoxetine in refractory SMA syndrome with comorbid
    DSM-5 somatic symptom disorder - the only registered pharmacotherapy trial in
    this disease. IMPORTANT SCOPE CAVEAT - this treats a psychiatric comorbidity
    that may amplify symptom burden, NOT the anatomic compression, and must not be
    generalised to routine SMA syndrome management. It is recorded here because the
    hypothesis (that reducing somatic-symptom amplification can avert
    duodenojejunostomy) bears directly on the disease's symptom-driven vicious
    cycle.
  evidence:
  - reference: clinicaltrials:NCT07115472
    reference_title: "Fluoxetine as a Non-Surgical Intervention for Refractory Superior Mesenteric Artery Syndrome With Comorbid Somatic Symptom Disorder: A Prospective Case Series Study"
    supports: SUPPORT
    snippet: "Can psychiatric intervention targeting SSD reduce the likelihood of requiring duodenojejunostomy in refractory SMAS?"
    explanation: >
      States the trial's scope - a psychiatric comorbidity intervention tested for
      its effect on the need for surgery, not a treatment of the compression itself.

discussions:
- discussion_id: smas_no_molecular_lesion
  prompt: >
    Is there any molecular, genetic, or cellular determinant of susceptibility to
    SMA syndrome, beyond bulk visceral adiposity and skeletal geometry?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Mesenteric Fat Pad Depletion
  rationale: >
    SMA syndrome is curated here as a purely biomechanical disorder with no causal
    gene, pathogenic variant, inheritance pattern, molecular biomarker, or omics
    signature established. Yet only a minority of severely underweight patients
    develop it, implying unmodelled determinants of susceptibility - for example
    constitutional differences in the fixation and length of the ligament of Treitz,
    in SMA origin height or take-off angle, in the regional lipolytic behaviour of
    the mesenteric fat depot versus other depots, or in mesenteric connective-tissue
    laxity. Rare familial reports exist but have not been resolved to a mechanism.
    Whether these determinants are anatomic-variant, connective-tissue, or
    adipose-biology in nature is entirely open.
  proposed_experiments:
  - experiment_id: smas_depot_lipolysis
    name: Depot-resolved mesenteric adipose mobilisation study
    description: >
      Depot-resolved imaging or adipose sampling asking whether the mesenteric fat
      depot is preferentially mobilised in patients who develop SMA syndrome
      compared with BMI-matched controls who do not.
    decision_criterion: >
      Preferential mesenteric-depot loss in cases versus matched controls would
      support a depot-specific adipose-biology determinant of susceptibility.
  - experiment_id: smas_pre_post_geometry
    name: Prospective pre/post weight-loss aortomesenteric geometry cohort
    description: >
      Prospective CT or ultrasound cohorts measuring aortomesenteric angle,
      aortomesenteric distance, SMA origin height, and ligament-of-Treitz position
      before and after comparable weight loss, to identify pre-existing geometric
      predisposition.
    decision_criterion: >
      Baseline geometric parameters that predict incident SMA syndrome independently
      of the magnitude of weight loss would establish anatomic predisposition.
  - experiment_id: smas_connective_tissue_phenotyping
    name: Connective-tissue phenotyping of SMA syndrome cohorts
    description: >
      Systematic assessment of joint hypermobility and established heritable
      connective-tissue disease in SMA syndrome cohorts versus controls.
    decision_criterion: >
      Enrichment of connective-tissue laxity in cases would implicate mesenteric
      connective-tissue properties as a susceptibility determinant.

- discussion_id: smas_threshold_variability
  prompt: >
    What aortomesenteric angle and distance thresholds should define SMA syndrome,
    and should they be adjusted for age, BMI, sex, population, and imaging technique?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Aortomesenteric Angle and Distance Narrowing
  rationale: >
    One population-specific cross-sectional series reported a mean
    aortomesenteric angle of 54.07 +/- 8.53 degrees and a mean distance of 16.25 +/-
    3.44 mm, while a prospective clinical cohort used 22 degrees or less and 8 mm or
    less as operational thresholds. Because the angle and distance correlate
    directly with BMI - which is itself the disease's principal risk factor - a
    fixed threshold necessarily entangles the exposure with the diagnostic
    criterion, and narrowed geometry occurs in asymptomatic individuals.
    Population- and age-specific normative studies are actively being conducted but
    have not yet produced adjusted criteria.
  evidence:
  - reference: PMID:30291587
    reference_title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis was achieved through barium swallow, CT/MR angiography (aortomesenteric angle ≤ 22°, distance ≤ 8 mm), endoscopy."
    explanation: >-
      Documents the operational angle and distance thresholds used in a prospective
      clinical cohort.
  - reference: PMID:38694377
    reference_title: "Evaluating aortomesenteric parameters in a tertiary center of Nepal for superior mesenteric artery syndrome diagnosis and risk factors: cross-sectional study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Understanding these normal values in the Nepalese population is critical for accurate diagnoses and predictions using CT scans. The research highlights the impact of demographic factors on these parameters and emphasizes their significance in clinical assessments related to SMA syndrome."
    explanation: >
      Argues explicitly that population-specific normative aortomesenteric values are
      needed rather than a single universal threshold.
  - reference: clinicaltrials:NCT03937193
    reference_title: "Normal Range of Superior Mesenteric Artery on Computerized Tomography in Young Chinese Population and Its Correlation With Retroperitoneal Adipose Tissue"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In literature, superior mesenteric artery (SMA) angle, also named as aortomesenteric angle (AMA), varies greatly in both adult and children; while the aortomesenteric distance also ranges widely. Both AMA and AMD are influenced by retroperitoneal fat."
    explanation: >
      Registered normative study confirming both the wide literature variation in
      aortomesenteric geometry and its confounding by retroperitoneal fat - the two
      halves of this knowledge gap.
  - reference: clinicaltrials:NCT04515251
    reference_title: "A Prospective, Observational, Multicenter Study on Ultrasound Evaluation of Superior Mesenteric Artery Measurements in a Healthy Pediatric Population"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Multicenter, prospective, observational research project on children aged from 10 to 15 years old undergoing abdominal ultrasound examinations during routine clinical practice."
    explanation: >
      Shows that age-specific paediatric normative work is actively underway but not
      yet reported, substantiating the claim that adjusted criteria do not yet exist.
  proposed_experiments:
  - experiment_id: smas_normative_multipopulation
    name: Multi-population normative aortomesenteric reference study
    description: >
      Normative CT and ultrasound studies across multiple populations, stratified by
      age, sex, BMI, and measured visceral fat, deriving percentile-based rather
      than fixed thresholds.
    decision_criterion: >
      Demonstration that percentile-based, covariate-adjusted thresholds outperform a
      single fixed cut-off would justify replacing the current criteria.
  - experiment_id: smas_threshold_accuracy
    name: Prospective diagnostic-accuracy study of candidate thresholds
    description: >
      Prospective study comparing candidate angle and distance thresholds against a
      reference standard combining compatible symptoms with demonstrated duodenal
      transit obstruction, reporting sensitivity, specificity, and positive
      predictive value.
    decision_criterion: >
      A threshold pair with acceptable positive predictive value against the
      composite reference standard would define operational diagnostic criteria.

notes: >
  Curation notes. (1) SMA syndrome is deliberately curated as a non-Mendelian,
  mechanical/anatomic disorder: no gene, variant, inheritance pattern, molecular
  pathway, biomarker, omics signature, or validated animal model is established,
  and those sections are intentionally empty rather than speculatively filled.
  GeneReviews has no article for this disorder (confirmed by PubMed search), as
  expected for a non-Mendelian entity. (2) The pathograph is deliberately CYCLIC.
  The edge "Progressive Weight Loss and Malnutrition" -> "Mesenteric Fat Pad
  Depletion" closes a positive-feedback loop with the intervening nodes; every edge
  of the loop carries the hypothesis group `fat_pad_depletion_vicious_cycle`. This
  is not a modelling error - the self-amplifying cycle is the clinically decisive
  feature of the disease and the reason therapy targets nutrition rather than
  symptoms. (3) Do NOT conflate with nutcracker syndrome (left renal vein
  entrapment by the same aortomesenteric angle - modelled here as a differential
  diagnosis with an explicitly shared anatomic substrate), median arcuate ligament
  syndrome (coeliac axis compression by the diaphragm), or SMA
  thrombosis/embolism/dissection and mesenteric ischaemia (occlusive vascular
  disease of the artery itself). In SMA syndrome the artery is structurally normal;
  it is the compressing structure, not the diseased one. (4) Historical case-based
  literature reports mortality up to 33% in untreated or severely delayed disease.
  That figure was not carried into the entry as a structured claim because it
  derives from selected historical series with substantial ascertainment bias and no
  verifiable quotable source was located.

references:
- reference: PMID:37383896
  title: "Superior mesenteric artery syndrome: Diagnosis and management."
- reference: PMID:30291587
  title: "Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution."
- reference: PMID:31998513
  title: "Superior mesenteric artery syndrome in severe anorexia nervosa: A case series."
- reference: PMID:17476104
  title: "Recalling superior mesenteric artery syndrome."
- reference: PMID:31127323
  title: "Superior mesenteric artery syndrome: a radiographic review."
- reference: PMID:33905850
  title: "Superior Mesenteric Artery Syndrome Following Scoliosis Surgery: A Systematic Review of Case Reports."
- reference: PMID:39118170
  title: "Superior mesenteric artery syndrome following spine surgery in idiopathic adolescent scoliosis: a systematic review."
- reference: PMID:23959808
  title: "Superior mesenteric artery syndrome and its associated gastrointestinal implications."
- reference: PMID:29204239
  title: "Wilkie's syndrome."
- reference: PMID:39191411
  title: "Laparoscopic Surgery for Superior Mesenteric Artery Syndrome."
- reference: PMID:28356803
  title: "Superior mesenteric artery syndrome."
- reference: PMID:38694377
  title: "Evaluating aortomesenteric parameters in a tertiary center of Nepal for superior mesenteric artery syndrome diagnosis and risk factors: cross-sectional study."
- reference: PMID:36846354
  title: "Superior Mesenteric Artery Syndrome: A Vicious Cycle?"
- reference: PMID:37494487
  title: "Superior Mesenteric Artery Syndrome."
📚

References & Deep Research

References

14
PMID:37383896
Superior mesenteric artery syndrome: Diagnosis and management.
No top-level findings curated for this source.
PMID:30291587
Superior Mesenteric Artery Syndrome: a Prospective Study in a Single Institution.
No top-level findings curated for this source.
PMID:31998513
Superior mesenteric artery syndrome in severe anorexia nervosa: A case series.
No top-level findings curated for this source.
PMID:17476104
Recalling superior mesenteric artery syndrome.
No top-level findings curated for this source.
PMID:31127323
Superior mesenteric artery syndrome: a radiographic review.
No top-level findings curated for this source.
PMID:33905850
Superior Mesenteric Artery Syndrome Following Scoliosis Surgery: A Systematic Review of Case Reports.
No top-level findings curated for this source.
PMID:39118170
Superior mesenteric artery syndrome following spine surgery in idiopathic adolescent scoliosis: a systematic review.
No top-level findings curated for this source.
PMID:23959808
Superior mesenteric artery syndrome and its associated gastrointestinal implications.
No top-level findings curated for this source.
PMID:29204239
Wilkie's syndrome.
No top-level findings curated for this source.
PMID:39191411
Laparoscopic Surgery for Superior Mesenteric Artery Syndrome.
No top-level findings curated for this source.
PMID:28356803
Superior mesenteric artery syndrome.
No top-level findings curated for this source.
PMID:38694377
Evaluating aortomesenteric parameters in a tertiary center of Nepal for superior mesenteric artery syndrome diagnosis and risk factors: cross-sectional study.
No top-level findings curated for this source.
PMID:36846354
Superior Mesenteric Artery Syndrome: A Vicious Cycle?
No top-level findings curated for this source.
PMID:37494487
Superior Mesenteric Artery Syndrome.
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Superior Mesenteric Artery Syndrome: Disease-Characteristics Report
Edison Scientific Literature 12 citations 2026-08-01T17:15:51.141803

Superior Mesenteric Artery Syndrome: Disease-Characteristics Report

Scope and evidence note. Superior mesenteric artery syndrome (SMAS) is rare, and its literature is dominated by retrospective cohorts, small prospective series, and case reports rather than large randomized trials. The most recent 2023–2024 literature located was primarily surgical or case-based; therefore, foundational reviews and the prospective cohort indexed as PMID 30291587 remain important. Numerical epidemiologic and mortality estimates should be treated cautiously because they often derive from older, selected series rather than population registries.

Domain Summary Key structured fields / suggested mappings Evidence
Definition / category Superior Mesenteric Artery Syndrome (SMAS, Wilkie syndrome) is a rare structural/acquired duodenal obstruction caused by compression of the third/horizontal duodenum in the narrowed space between the abdominal aorta and superior mesenteric artery. Category: Structural; Disease class: duodenal obstruction / gastrointestinal compression syndrome (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 1-2, NCT03416647 chunk 1)
Identifiers / synonyms Secure identifier present in evidence: MeSH D013478. Synonyms documented in retrieved evidence include Wilkie syndrome, chronic duodenal obstruction, and CAST syndrome. A prospective institutional study is linked to PMID 30291587; relevant trials include NCT03416647, NCT07115472, NCT04515251, NCT03937193, NCT06970093. Exact IDs asserted: MeSH D013478; PMID 30291587; NCT03416647; NCT07115472; NCT04515251; NCT03937193; NCT06970093 (galimov2022thecomplicationof pages 3-4, NCT03416647 chunk 1, NCT07115472 chunk 1, NCT04515251 chunk 1, NCT06970093 chunk 1, NCT03937193 chunk 1)
Core anatomy Primary lesion site is the third/transverse/horizontal part of the duodenum compressed between the SMA anteriorly and abdominal aorta/spine posteriorly; retroperitoneal fat loss narrows this space. Suggested anatomy labels: duodenum (3rd part), superior mesenteric artery, abdominal aorta, retroperitoneal fat pad (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 3-4, galimov2022thecomplicationof pages 1-2, NCT03937193 chunk 1)
Major phenotypes Core phenotype cluster: postprandial epigastric/abdominal pain, nausea, vomiting, reflux, bloating, difficulty eating, weight loss, low BMI/underweight, sometimes severe complications such as aspiration pneumonia or acute pancreatitis. Suggested HPO labels: abdominal pain; epigastric pain; nausea; vomiting; abdominal bloating; gastroesophageal reflux; early satiety/feeding difficulty; weight loss; low body mass index; malnutrition; dehydration (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 3-4, NCT03416647 chunk 1, NCT07115472 chunk 1, NCT06970093 chunk 1)
Mechanism / causal chain Typical causal chain: rapid weight loss or altered anatomy → loss/reduction of retroperitoneal fat cushion → decreased aortomesenteric angle/distance → extrinsic compression of D3 → impaired chyme passage / proximal obstruction → meal-related symptoms, reduced intake, further weight loss, and possible severe gastric or aspiration/pancreatic complications. Suggested process labels: intestinal obstruction; impaired gastric emptying/proximal stasis; nutritional deficiency; positive feedback worsening via weight loss (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 3-4, NCT03416647 chunk 1, galimov2022thecomplicationof pages 4-5, NCT03937193 chunk 1)
Diagnostic imaging thresholds Diagnosis is imaging-centered and usually combines symptoms with CT/MR angiography and/or contrast studies. Evidence shows normal aortomesenteric angle roughly 35–65° or 38–80° and distance 10–28 mm; commonly used abnormal thresholds are angle <22° and distance <8 mm; broader abnormal cutoffs <35° and <10 mm also appear in case literature. Imaging modalities in evidence: CT with oral contrast, CT/MR angiography, suggestive barium swallow; example case: angle 14°, distance 6 mm (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 3-4, galimov2022thecomplicationof pages 1-2, NCT03416647 chunk 1, NCT07115472 chunk 1)
Major acquired risk factors Major non-genetic/acquired drivers are rapid weight loss, underweight/low BMI, feeding difficulty, and anatomic distortion; trial exclusion/observational protocols also flag conditions such as severe scoliosis/spinal fixation, abdominal masses, and cachectic states as relevant anatomical confounders/risk contexts. Suggested risk labels: rapid weight loss; low BMI; loss of retroperitoneal adipose tissue; postoperative/anatomic change; scoliosis-associated distortion (galimov2022thecomplicationof pages 2-3, NCT03416647 chunk 1, NCT07115472 chunk 1, NCT04515251 chunk 1, NCT03937193 chunk 1)
First-line management Initial management is generally conservative: restore nutrition/weight, treat dehydration/electrolyte problems, decompress when needed, and use medical/supportive therapy; the refractory-SMAS trial defines failed conservative care as failure of gastrointestinal decompression, enteral nutrition, and parenteral nutrition. Suggested intervention labels: nutritional rehabilitation; enteral nutrition; parenteral nutrition; gastrointestinal decompression; symptom-directed medical therapy (galimov2022thecomplicationof pages 3-4, NCT03416647 chunk 1, NCT07115472 chunk 1)
Surgical management For persistent/refractory disease, duodenojejunostomy is the most consistently represented operation in the evidence and was used for all patients in the prospective single-institution study; case evidence also describes laparoscopic Strong’s operation / duodenal mobilization strategies. A randomized trial is comparing One Anastomosis Gastric Bypass (OAGB) vs Duodenojejunostomy (DJ). Exact trial/intervention IDs: NCT03416647 (duodenojejunostomy cohort), NCT06970093 (OAGB vs DJ); suggested NCIT-style labels: duodenojejunostomy; gastric bypass procedure (galimov2022thecomplicationof pages 1-2, NCT03416647 chunk 1, NCT06970093 chunk 1, NCT06970093 chunk 2)
Epidemiology SMAS is rare. Retrieved case literature reports prevalence estimates around 0.1%–0.78%, female predominance around 2:1, and peak occurrence in 10–30 years, though it can occur outside this range. One CT normative study planned 500 non-SMAS vs 10 SMAS cases in a young Chinese cohort, illustrating rarity in imaging datasets. Epidemiology fields: rare disease; female predominance; pediatric-to-young-adult skew with broader age range possible (galimov2022thecomplicationof pages 2-3, NCT03937193 chunk 1)
Prognosis / complications Prognosis improves with timely recognition and decompressive treatment. Documented serious complications include gastric perforation, acute pancreatitis, aspiration pneumonia, ulcer disease, and in older literature/case review life-threatening deterioration with reported mortality up to 33% if untreated. Prospective studies track symptom scores, BMI recovery, and reduced need for acid suppression/prokinetics over long follow-up. Outcome fields: symptom relief; BMI gain; complication prevention; long-term follow-up in prospective cohort median 47 months (IQR 34–72) (galimov2022thecomplicationof pages 2-3, NCT03416647 chunk 1, galimov2022thecomplicationof pages 4-5)
Evidence gaps (genetics / omics / models) No secure evidence in the retrieved materials supports a causal gene, pathogenic variant, Mendelian inheritance pattern, molecular biomarker, omics signature, infectious etiology, or validated model organism. Current evidence base is dominated by clinical imaging studies, case reports/series, and small interventional cohorts/trials. KB note: mark genetics/omics/animal-model fields as not established in retrieved evidence rather than negative (NCT03416647 chunk 1, NCT07115472 chunk 1, NCT03937193 chunk 1)

Table: This table condenses the highest-yield disease-characteristics fields for Superior Mesenteric Artery Syndrome, including secure identifiers, anatomy, phenotypes, mechanism, diagnostic thresholds, treatment, epidemiology, and major evidence gaps. It is designed for direct use in a structured disease knowledge base.

1. Disease information

Definition

SMAS is an extrinsic mechanical obstruction of the third, horizontal portion of the duodenum (D3) where it passes between the superior mesenteric artery (SMA) anteriorly and the abdominal aorta/spine posteriorly. Reduction of the intervening mesenteric-retroperitoneal fat cushion narrows the aortomesenteric angle and distance, compressing D3. It is a structural gastrointestinal compression syndrome, not mesenteric ischemia or SMA dissection. (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 3-4, galimov2022thecomplicationof pages 1-2)

A useful exact abstract quotation from Galimov et al. (published July 2022) is: “the distal part of the duodenum is compressed between the abdominal aorta, spine, and SMA,” producing mechanical obstruction. The authors also emphasize that delayed diagnosis may lead to life-threatening complications. DOI: https://doi.org/10.24060/2076-3093-2022-12-2-123-127. (galimov2022thecomplicationof pages 1-2)

Identifiers and synonyms

  • MeSH: D013478, Superior Mesenteric Artery Syndrome—securely present in the retrieved ClinicalTrials.gov records. (NCT03416647 chunk 1)
  • MONDO, OMIM, Orphanet, ICD-10, ICD-11: an exact current identifier was not securely recovered from the accessed evidence and should be verified directly against the live ontology release before knowledge-base ingestion. SMAS is not established as an OMIM Mendelian disorder.
  • Synonyms: Wilkie syndrome/Wilkie’s syndrome; chronic duodenal obstruction; arteriomesenteric duodenal compression syndrome; cast syndrome/CAST syndrome. “Chronic duodenal obstruction” and “Wilkie’s syndrome” occur in the prospective-study record. (galimov2022thecomplicationof pages 3-4, NCT03416647 chunk 1)
  • Do not conflate with: SMA thrombosis, embolism, dissection, aneurysm, or acute/chronic mesenteric ischemia.

The report describes aggregated disease-level evidence. The cited prospective study included 39 consecutive patients; no individual EHR-derived patient record is used here. (NCT03416647 chunk 1)

2. Etiology

Causal and predisposing factors

The best-established causal sequence is rapid or substantial weight loss → depletion of the aortomesenteric fat pad → narrowing of the aortomesenteric angle/distance → D3 compression. Once obstruction impairs eating, further weight loss can create a self-amplifying cycle. (galimov2022thecomplicationof pages 2-3, NCT03937193 chunk 1)

Recognized clinical contexts include:

  • severe or rapid weight loss, low BMI, malnutrition, cachexia, or feeding restriction;
  • eating disorders and other illnesses causing reduced intake or catabolism;
  • major burns, trauma, malignancy, malabsorption, prolonged immobilization, or severe systemic illness;
  • corrective spinal surgery, marked scoliosis, body casting, or rapid linear growth, which can alter the relationship between the SMA, aorta, spine, and duodenum;
  • abdominal or retroperitoneal operations that change intestinal fixation or tension.

The prospective surgical protocol regarded BMI below 18.5 kg/m² with difficulty eating as a major clinical feature. Imaging studies specifically examine BMI, visceral fat, and retroperitoneal fat because these influence angle and distance; severe scoliosis and spinal fixation are treated as important anatomical modifiers. (NCT03416647 chunk 1, NCT04515251 chunk 1, NCT03937193 chunk 1)

Genetics, environment, and protective factors

No validated causal gene, susceptibility locus, pathogenic variant, modifier gene, Mendelian inheritance pattern, or gene–environment interaction has been established. Congenital/anatomical configurations may predispose an individual, but that is not equivalent to a demonstrated genetic disorder.

No toxin, pollutant, occupational exposure, or infectious agent is established as a direct cause. Lifestyle and environmental effects are principally mediated through nutritional depletion or acquired anatomical change. Maintaining adequate nutrition and avoiding rapid, unmonitored weight loss in vulnerable patients are plausible protective measures, but no controlled study establishes a specific protective diet, allele, drug, or supplement.

3. Phenotypes

SMAS can occur in children or adults and may present acutely after a precipitating event or insidiously over months or years. Severity ranges from intermittent postprandial discomfort to complete high intestinal obstruction and severe malnutrition. The 39-patient protocol defined clinically important disease through severe symptoms occurring at least weekly, poor quality of life, refractory response to medical treatment, underweight, or serious complications. (NCT03416647 chunk 1)

Phenotype Type/course and impact Suggested HPO annotation
Postprandial epigastric or upper-abdominal pain Symptom; episodic after meals or persistent in advanced obstruction; limits eating and activity Epigastric pain; Abdominal pain
Nausea and bilious/non-bilious vomiting Symptoms; intermittent to severe; may cause dehydration and aspiration Nausea; Vomiting
Early satiety, feeding difficulty, bloating, reflux Symptoms; worsened by meals; substantially impairs nutrition and social eating Early satiety; Feeding difficulties; Abdominal distention; Gastroesophageal reflux
Weight loss, underweight, low BMI Physical/nutritional phenotype; often progressive and both cause and consequence Weight loss; Decreased body weight; Low body mass index
Malnutrition/dehydration/electrolyte disturbance Laboratory/systemic consequences; severity varies with duration Malnutrition; Dehydration; Electrolyte abnormality
Gastric and proximal duodenal dilation Imaging/physical manifestation of obstruction Duodenal obstruction; Gastric dilatation
Aspiration pneumonia, acute pancreatitis, gastric perforation Uncommon but severe complications Aspiration pneumonia; Acute pancreatitis; Gastrointestinal perforation

Abdominal pain, nausea, vomiting, reflux, and bloating were explicitly captured in the prospective cohort’s symptom score; severe complications included gastric perforation, acute pancreatitis, and aspiration pneumonia. (NCT03416647 chunk 1)

Formal SMAS-specific EQ-5D, SF-36, or PROMIS norms were not identified. Nevertheless, inability to tolerate meals, recurrent vomiting, nutritional dependence, and chronic pain can markedly impair physical, psychological, educational, occupational, and social functioning. The prospective study explicitly required poor quality of life for one clinical inclusion pathway. (NCT03416647 chunk 1)

4. Genetic and molecular information

SMAS is not currently defined by a molecular lesion. No causal gene, HGNC identifier, pathogenic germline or somatic variant, variant class, allele frequency, penetrance, anticipation, founder effect, carrier frequency, modifier gene, epigenetic defect, or recurrent chromosomal abnormality was identified.

Accordingly:

  • ClinVar-style variant classification: not applicable.
  • WES/WGS, gene panels, CMA, karyotyping, FISH, mtDNA, and repeat-expansion testing: not indicated for diagnosing SMAS itself.
  • Genetic evaluation may be appropriate only when a separate syndromic, connective-tissue, developmental, or neuromuscular disorder is clinically suspected.
  • No validated pharmacogenomic recommendation exists for SMAS treatment.

5. Environmental and lifestyle information

The clinically meaningful “environmental” exposures are circumstances producing weight loss or anatomical distortion rather than toxicants. Restrictive eating, inadequate caloric intake, prolonged illness, catabolic states, spinal correction, and postoperative anatomical changes are the principal acquired contexts. Retroperitoneal fat is directly relevant: a 510-participant CT study was designed to relate aortomesenteric geometry to visceral and subcutaneous fat, with 500 non-SMAS and 10 SMAS participants. (NCT03937193 chunk 1)

Smoking and alcohol have no established disease-specific causal association. Exercise is not intrinsically causal, although extreme energy imbalance could contribute indirectly. No bacterial, viral, fungal, or parasitic trigger is established.

6. Mechanism and pathophysiology

Causal chain

  1. Upstream trigger: rapid weight loss, low visceral fat, altered spinal/mesenteric anatomy, or postoperative tension.
  2. Structural intermediate: reduced fat cushion and narrowing of the SMA–aorta angle and distance.
  3. Primary lesion: extrinsic compression of D3.
  4. Functional consequence: impaired chyme passage, proximal duodenal/gastric stasis and dilation, vomiting, reflux, and postprandial pain.
  5. Downstream systemic effects: reduced intake, dehydration, electrolyte abnormalities, malnutrition, and additional fat loss.
  6. Complications: mucosal injury/ulceration, aspiration, perforation, pancreatitis, and potentially severe metabolic deterioration. (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 3-4, NCT03416647 chunk 1, galimov2022thecomplicationof pages 4-5)

This is principally a biomechanical obstruction. No disease-defining Wnt, MAPK, mTOR, PI3K–AKT, immune, inflammatory, apoptotic, autophagic, protein-folding, receptor, ion-channel, or enzyme-deficiency pathway is established. Likewise, no reproducible transcriptomic, proteomic, metabolomic, lipidomic, single-cell, spatial-transcriptomic, multi-omic, or CRISPR-screen signature was identified.

Suggested GO biological-process labels: digestive-system process; gastrointestinal motility; regulation of body weight; response to nutrient; intestinal absorption. These are annotation suggestions, not demonstrated molecular mechanisms. Relevant cell populations are ordinary duodenal epithelium, smooth-muscle cells, enteric neurons, vascular endothelial/smooth-muscle cells, and adipocytes; none is a selectively diseased cell type. Suggested CL labels therefore include enterocyte, intestinal epithelial cell, smooth-muscle cell, enteric neuron, endothelial cell, and adipocyte.

7. Anatomical structures affected

  • Primary organ/site: D3, the horizontal/transverse duodenum.
  • Compression boundaries: SMA anteriorly; abdominal aorta and vertebral column posteriorly.
  • Relevant tissue: the aortomesenteric/retroperitoneal adipose cushion.
  • Secondary involvement: proximal duodenum and stomach through dilation and stasis; esophagus and lungs through reflux/aspiration; pancreas in rare obstructive pancreatitis.
  • Body systems: primarily digestive; secondarily nutritional/metabolic and respiratory.
  • Lateralization: not applicable.
  • Subcellular compartment: none specifically implicated.

Suggested UBERON labels are duodenum, third part of duodenum, superior mesenteric artery, abdominal aorta, retroperitoneal region, adipose tissue, stomach, and vertebral column. Exact ontology IDs should be mapped against the selected UBERON release rather than inferred from names.

8. Temporal development

Onset can be acute following rapid weight loss, trauma, or spinal/abdominal surgery, or chronic and insidious. The highest reported occurrence is in adolescents and young adults, but disease is documented across childhood, adulthood, and older age. One reviewed source reports a peak at 10–30 years. (galimov2022thecomplicationof pages 2-3)

There is no universally accepted stage system. A practical clinical sequence is:

  1. intermittent postprandial symptoms;
  2. persistent obstruction with reduced intake and weight loss;
  3. severe nutritional/metabolic compromise or complications;
  4. recovery after restoration of the fat cushion or surgical bypass.

The course may remit with successful weight restoration, recur if weight is again lost, or remain chronic if obstruction and nutritional depletion perpetuate each other. The principal intervention window is before profound malnutrition, aspiration, perforation, or other complications develop.

9. Inheritance and population epidemiology

Reported prevalence estimates vary approximately from 0.1% to 0.78% in selected radiographic or clinical populations, with a reported female-to-male ratio near 2:1 and concentration in the 10–30-year age range. These are not robust population-incidence estimates and should not be interpreted as contemporary global prevalence. No reliable annual incidence per 100,000 was identified. (galimov2022thecomplicationof pages 2-3)

No established ethnic founder population, endemic geography, consanguinity association, carrier state, penetrance, or expressivity framework applies. Geographic differences are likely dominated by referral patterns, nutritional exposures, surgical practice, and ascertainment. The Chinese normative CT study illustrates active work to derive population-specific reference distributions rather than assuming one universal angle or distance threshold. (NCT03937193 chunk 1)

10. Diagnostics

Diagnostic approach

Diagnosis requires both a compatible obstructive phenotype and imaging evidence of D3 compression. A narrow angle or distance alone can occur without symptomatic SMAS and should not be treated as diagnostic in isolation.

Preferred imaging: contrast-enhanced abdominal CT with sagittal reconstruction measures the aortomesenteric angle; axial images measure distance and show D3 compression and proximal gastric/duodenal dilation. CT or MR angiography can define vascular geometry. Oral water-soluble contrast or an upper-GI/barium series may show proximal dilation, abrupt hold-up at D3, delayed transit, and sometimes positional improvement. Ultrasound can measure angle/distance without radiation but is operator- and body-habitus-dependent. (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 3-4, galimov2022thecomplicationof pages 1-2, NCT03416647 chunk 1)

Commonly used values are:

  • normal angle approximately 35–65° or 38–80°;
  • normal distance approximately 10–28 mm;
  • strongly suggestive abnormal geometry: angle <22° and/or distance <8 mm;
  • broader case-literature cutoffs: angle <35° and distance <10 mm.

A published case measured 14° and 6 mm. Variation in normal and abnormal cutoffs reinforces the need for clinical-radiological concordance. (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 3-4, NCT07115472 chunk 1)

A current pediatric observational study, NCT04515251, is prospectively establishing age-, BMI-, and fat-adjusted ultrasound ranges in 289 children aged 10–15 years, highlighting that pediatric reference standards remain under development. ClinicalTrials.gov: https://clinicaltrials.gov/study/NCT04515251. (NCT04515251 chunk 1)

Laboratory and other testing

There is no disease-specific blood, urine, tissue, genetic, or circulating biomarker. Laboratory studies assess consequences and alternative diagnoses: CBC, electrolytes, bicarbonate, renal and hepatic function, glucose, magnesium, phosphate, calcium, albumin/prealbumin with appropriate caution, inflammatory markers, lipase, and nutritional deficiencies. Endoscopy may exclude luminal lesions and evaluate retained contents or mucosal injury but cannot by itself establish extrinsic D3 compression. Biopsy, electrophysiology, PET, and omics testing have no routine role.

Differential diagnosis

Important alternatives include gastroparesis, functional dyspepsia, cyclic vomiting/cannabinoid hyperemesis, eating disorders, peptic ulcer disease, pancreatitis, annular pancreas, malrotation/Ladd bands, duodenal web or tumor, Crohn disease, retroperitoneal mass, adhesions, chronic intestinal pseudo-obstruction, and other vascular-compression syndromes. Malignancy, motility disorders, and severe psychiatric illness were specifically excluded from the prospective surgical protocol, illustrating the need to avoid attributing nonspecific symptoms to incidental vascular geometry. (NCT03416647 chunk 1)

There is no population, newborn, carrier, or cascade screening program. Targeted imaging is reasonable in a high-risk patient with rapid weight loss or recent spinal surgery who develops persistent postprandial pain and vomiting.

11. Outcome and prognosis

Timely diagnosis and reversal or bypass of obstruction generally permit nutritional recovery and symptom improvement. A prospective cohort enrolled 39 patients, all treated with duodenojejunostomy, and assessed symptoms, BMI, and medication requirements at a median 47 months (IQR 34–72). PMID 30291587; publication: Journal of Gastrointestinal Surgery, May 2019; https://pubmed.ncbi.nlm.nih.gov/30291587/. (NCT03416647 chunk 1)

A 2022 case had an uncomplicated postoperative course, pain relief, weight gain, and discharge nine days after surgery. This is illustrative but not a population response rate. (galimov2022thecomplicationof pages 3-4, galimov2022thecomplicationof pages 1-2)

Potential morbidity includes chronic pain, inability to eat, malnutrition, dehydration, electrolyte disorders, aspiration pneumonia, acute pancreatitis, gastric perforation, ulcer disease, and repeated hospitalization. Older case-based literature reports mortality as high as 33% in untreated or severely delayed disease, but this figure is likely affected by historical care and selection bias and should not be presented as a modern average mortality rate. (galimov2022thecomplicationof pages 2-3, galimov2022thecomplicationof pages 4-5)

No validated five- or ten-year survival estimate, life-expectancy decrement, prognostic molecular biomarker, or disease-specific quality-of-life instrument was identified. Favorable factors are early recognition, reversible weight-loss trigger, successful nutritional restoration, and absence of severe complications; persistent symptoms despite adequate nutrition and coexisting motility or functional disorders complicate prognosis.

12. Treatment

Initial conservative management

For a hemodynamically stable patient without perforation or another surgical emergency:

  1. nasogastric decompression when vomiting or marked dilation is present;
  2. intravenous fluid, electrolyte, and acid–base correction;
  3. antiemetic and symptom-directed therapy;
  4. small, frequent, energy-dense meals when tolerated;
  5. enteral feeding distal to the obstruction, such as nasojejunal feeding, if oral intake is inadequate;
  6. parenteral nutrition when enteral feeding is impossible or insufficient;
  7. positional maneuvers—left lateral decubitus, prone, or knee-chest—may transiently reduce compression;
  8. multidisciplinary treatment of the precipitating illness or eating disorder.

The objective is weight restoration and reconstitution of the fat pad, not merely suppression of nausea. The refractory-SMAS trial operationally defines failed conservative therapy as failure of decompression, enteral nutrition, and parenteral nutrition. (NCT07115472 chunk 1)

Suggested NCIT-style intervention labels include Gastrointestinal Decompression, Enteral Nutrition, Parenteral Nutrition, Nutritional Support, and Antiemetic Therapy. No SMAS-specific pharmacotherapy is approved, and no pharmacogenomic algorithm applies.

Surgery and intervention

Laparoscopic duodenojejunostomy bypasses the compressed segment and is the best-supported definitive operation for refractory disease. Indications include persistent obstruction despite an adequate nutritional trial, inability to restore weight, recurrent hospitalization, severe complications, or a fixed anatomical cause. The 39-patient prospective cohort used duodenojejunostomy, with or without duodenal resection. (NCT03416647 chunk 1)

Other operations include Strong’s procedure—division of the ligament of Treitz and duodenal mobilization—gastrojejunostomy, duodenal derotation, and selected alternative bypass procedures. Terminology must be used carefully: Strong’s procedure is anatomically distinct from duodenojejunostomy, although some case reports describe combined mobilization and anastomosis. A 2022 report achieved symptom resolution after laparoscopic operative treatment. (galimov2022thecomplicationof pages 3-4, galimov2022thecomplicationof pages 4-5)

Potential surgical adverse events include leak, bleeding, infection, delayed gastric emptying, persistent symptoms, adhesive obstruction, nutritional problems, and reoperation. Evidence comparing procedures remains limited.

Recent and ongoing clinical research

  • NCT03416647: completed, single-group prospective cohort; 39 participants; duodenojejunostomy; outcomes included symptom score, BMI, and medical-treatment need over median 47 months. The linked publication is PMID 30291587. https://clinicaltrials.gov/study/NCT03416647. (NCT03416647 chunk 1)
  • NCT06970093: small randomized, open-label comparison of one-anastomosis gastric bypass versus duodenojejunostomy; 20 participants, 12-month symptoms and BMI endpoints. Although enrollment began in March 2024, the registry was first posted in May 2025; no efficacy results were available in the retrieved record. https://clinicaltrials.gov/study/NCT06970093. (NCT06970093 chunk 1, NCT06970093 chunk 2)
  • NCT07115472: 45-patient single-group study of fluoxetine, 20–60 mg/day, in refractory SMAS specifically with DSM-5 somatic symptom disorder. This tests treatment of a comorbidity, not reversal of anatomical compression, and should not be generalized to routine SMAS. No posted efficacy result was retrieved. https://clinicaltrials.gov/study/NCT07115472. (NCT07115472 chunk 1)
  • NCT03937193: completed 510-participant CT study of angle, distance, and retroperitoneal fat in a young Chinese population. https://clinicaltrials.gov/study/NCT03937193. (NCT03937193 chunk 1)
  • NCT04515251: recruiting pediatric normative ultrasound study with estimated enrollment of 289 and estimated completion in December 2026. (NCT04515251 chunk 1)

Gene, cell, RNA, targeted molecular, and immunotherapies have no established role.

13. Prevention

Primary prevention

There is no vaccine, prophylactic medication, genetic screening, or universal prevention program. In high-risk settings, practical measures are nutritional assessment before and after major surgery, prevention of excessive perioperative weight loss, early dietitian involvement, and close monitoring of patients with severe scoliosis, spinal correction, catabolic illness, or restrictive eating.

Secondary prevention

Persistent vomiting and postprandial pain after rapid weight loss or spinal/abdominal surgery should prompt early imaging. Angle and distance should be interpreted with demonstrated duodenal obstruction rather than used as asymptomatic screening tests.

Tertiary prevention

Prevent recurrence and complications through sustained nutritional rehabilitation, treatment of the precipitating disorder, monitoring of weight/electrolytes, aspiration precautions when vomiting is severe, and timely surgery when conservative treatment fails. Genetic counseling and reproductive testing are not indicated for isolated SMAS.

14. Other species and natural disease

No well-characterized naturally occurring veterinary counterpart, breed predisposition, orthologous causal gene, zoonotic potential, or cross-species transmission was identified. Because SMAS is a mechanical relationship among the duodenum, SMA, aorta, spine, and fat pad, conceptually similar compression could occur in another species, but this should not be entered as a validated comparative-disease association without veterinary primary evidence.

15. Model organisms

No standardized mouse, rat, zebrafish, invertebrate, cellular, organoid, iPSC, knockout, knock-in, or humanized model was identified. Experimental manipulation of body weight or surgical alteration of mesenteric anatomy might model selected biomechanical features, but such an induced model would not reproduce the full human symptom complex and could create major welfare and translational limitations. Human CT/MR/ultrasound measurements, computational geometry, and clinical cohorts are currently more directly relevant than molecular model organisms.

Expert synthesis and knowledge-base recommendations

  1. Classify SMAS as an acquired structural duodenal-obstruction syndrome, not a genetic or primary vascular-occlusive disease.
  2. Encode the primary causal chain as loss of aortomesenteric adipose cushion/anatomical distortion → reduced angle and distance → extrinsic D3 compression → proximal obstruction → reduced intake and further weight loss.
  3. Require clinical-radiological concordance; <22° and <8 mm are supportive thresholds, not stand-alone diagnostic criteria. Population-, age-, BMI-, and technique-dependent reference variation remains an active research issue. (NCT07115472 chunk 1, NCT04515251 chunk 1, NCT03937193 chunk 1)
  4. Treat nutritional restoration and decompression as first-line care, with laparoscopic duodenojejunostomy as the principal definitive operation for persistent, fixed, or complicated disease. (NCT03416647 chunk 1)
  5. Mark gene, variant, inheritance, molecular pathway, omics, biomarker, animal-disease, and model-organism fields as “not established”, rather than filling them with speculative associations.
  6. Evidence certainty is moderate for the core anatomy and diagnostic concept, but low-to-moderate for exact epidemiology, optimal duration of conservative therapy, comparative surgical effectiveness, and long-term quality-of-life outcomes.

References

  1. (galimov2022thecomplicationof pages 2-3): O. V. Galimov, V. O. Khanov, H.M. H. Karkhani, Sh. Bhawna, and T. R. Ibragimov. The complication of decrease in aorto-mesenteric angle and distance its diagnosis and treatment: case report. Creative surgery and oncology, 12:123-127, Jul 2022. URL: https://doi.org/10.24060/2076-3093-2022-12-2-123-127, doi:10.24060/2076-3093-2022-12-2-123-127. This article has 0 citations.

  2. (galimov2022thecomplicationof pages 1-2): O. V. Galimov, V. O. Khanov, H.M. H. Karkhani, Sh. Bhawna, and T. R. Ibragimov. The complication of decrease in aorto-mesenteric angle and distance its diagnosis and treatment: case report. Creative surgery and oncology, 12:123-127, Jul 2022. URL: https://doi.org/10.24060/2076-3093-2022-12-2-123-127, doi:10.24060/2076-3093-2022-12-2-123-127. This article has 0 citations.

  3. (NCT03416647 chunk 1): Angelica Ganss. SMAS: a Prospective Study in a Single Institution. Azienda Ospedaliera di Padova. 2008. ClinicalTrials.gov Identifier: NCT03416647

  4. (galimov2022thecomplicationof pages 3-4): O. V. Galimov, V. O. Khanov, H.M. H. Karkhani, Sh. Bhawna, and T. R. Ibragimov. The complication of decrease in aorto-mesenteric angle and distance its diagnosis and treatment: case report. Creative surgery and oncology, 12:123-127, Jul 2022. URL: https://doi.org/10.24060/2076-3093-2022-12-2-123-127, doi:10.24060/2076-3093-2022-12-2-123-127. This article has 0 citations.

  5. (NCT07115472 chunk 1): Zhifeng Zhao, PhD. Fluoxetine in Refractory Superior Mesenteric Artery Syndrome by Targeting Comorbid Somatic Symptom Disorder. Xijing Hospital of Digestive Diseases. 2024. ClinicalTrials.gov Identifier: NCT07115472

  6. (NCT04515251 chunk 1): Marirosa Cristallo Lacalamita. Ultrasound Evaluation of Superior Mesenteric Artery Measurements in a Healthy Pediatric Population. Ente Ospedaliero Cantonale, Bellinzona. 2020. ClinicalTrials.gov Identifier: NCT04515251

  7. (NCT06970093 chunk 1): Comparison of One Anastomisis Gastric Bypass and Duodeno-Jejunostomy for Treating SMA Syndrome. Ain Shams University. 2024. ClinicalTrials.gov Identifier: NCT06970093

  8. (NCT03937193 chunk 1): Professor Winnie W.C. Chu. Normal Range of Superior Mesenteric Artery in Young Chinese Population and Its Correlation With Retroperitoneal Adipose Tissue. Chinese University of Hong Kong. 2019. ClinicalTrials.gov Identifier: NCT03937193

  9. (galimov2022thecomplicationof pages 4-5): O. V. Galimov, V. O. Khanov, H.M. H. Karkhani, Sh. Bhawna, and T. R. Ibragimov. The complication of decrease in aorto-mesenteric angle and distance its diagnosis and treatment: case report. Creative surgery and oncology, 12:123-127, Jul 2022. URL: https://doi.org/10.24060/2076-3093-2022-12-2-123-127, doi:10.24060/2076-3093-2022-12-2-123-127. This article has 0 citations.

  10. (NCT06970093 chunk 2): Comparison of One Anastomisis Gastric Bypass and Duodeno-Jejunostomy for Treating SMA Syndrome. Ain Shams University. 2024. ClinicalTrials.gov Identifier: NCT06970093

Artifacts