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Morgagni-Stewart-Morel Syndrome

Complex MONDO:0007766 Metabolic bone disease Endocrine disorder

Morgagni-Stewart-Morel syndrome is a rare condition characterized by the triad of hyperostosis frontalis interna (thickening of the inner table of the frontal bone), obesity, and neuropsychiatric disturbances. Additional features include endocrine disorders such as diabetes mellitus, diabetes insipidus, hyperparathyroidism, hyperprolactinemia, hirsutism, and menstrual irregularities. The syndrome predominantly affects postmenopausal women, with a female-to-male ratio of approximately 9:1. The etiology remains incompletely understood but is thought to involve endocrine imbalance driven by genetic and environmental factors, with prolonged estrogen exposure, elevated leptin levels, and growth hormone dysregulation implicated in the pathogenesis of the skull thickening.

1
Mappings
0
Definitions
1
Inheritance
4
Pathophysiology
0
Histopathology
12
Phenotypes
1
Genes
4
Treatments
0
Subtypes
3
Differentials
0
Datasets
0
Trials
🔗

Mappings

ICD-10-CM
ICD10CM:M85.2 Hyperostosis of skull
skos:closeMatch ICD-10-CM MONDO: MISSING
ICD-10-CM M85.2 covers hyperostosis of skull, which encompasses the defining feature of Morgagni-Stewart-Morel syndrome (hyperostosis frontalis interna). No specific ICD-10 code exists for the full syndrome.
👪

Inheritance

1
Autosomal dominant HP:0000006
Multiple-generation family studies and monozygotic twin concordance suggest autosomal dominant inheritance with incomplete penetrance and variable expressivity. Hyperostosis frontalis interna has been found in multiple generations of affected families, though no case of male-to-male transmission has been documented, and X-linked dominant inheritance has not been excluded.
Autosomal dominant inheritance Penetrance: INCOMPLETE Expressivity: VARIABLE
Show evidence (2 references)
PMID:16909048 SUPPORT Human Clinical
"We report two 71-year-old female monozygotic twins presenting with advanced hyperostosis frontalis interna, obesity, shortness and cognitive impairment. They both have suffered from generalized seizures since their early adulthood."
Monozygotic twin concordance for MSM syndrome features strongly supports a genetic basis for the disorder.
PMID:16909048 SUPPORT Human Clinical
"The symptoms common to both twins appear to correspond to the Morgagni-Stewart-Morel syndrome and indicate a genetic basis of this disorder as these features occur in genetically identical patients."
The authors explicitly conclude that the concordance in monozygotic twins indicates a genetic basis for MSM syndrome.
⚙

Pathophysiology

4
Endocrine-mediated calvarial bone overgrowth
The precise pathogenesis of frontal bone thickening remains unclear. Well-supported hypotheses include prolonged estrogen exposure stimulating osteoblastic activity in the frontal bone inner table (supported by large-scale anthropological studies) and elevated leptin levels associated with obesity promoting bone formation. A more contested hypothesis involves dysregulated growth hormone secretion from pituitary microadenomatosis; however, recent evidence shows no direct causative role for GH excess or hyperprolactinemia in HFI etiopathogenesis. The condition predominantly affects females and is associated with age, being much less frequent in females under 40 years.
Osteoblast link
Bone mineralization link Osteoblast differentiation link
Frontal bone link
Show evidence (5 references)
PMID:10407462 SUPPORT Human Clinical
"It is most commonly found among females and is believed to be associated with prolonged estrogen stimulation"
Establishes the estrogen hypothesis for HFI pathogenesis based on a large-scale anthropological study of over 1,700 skulls.
PMID:10407462 SUPPORT Human Clinical
"While its magnitude of manifestation and frequency are much higher in females, HFI is not a purely female phenomenon. Males with hormonal disturbances such as atrophic testis were found to manifest HFI type D."
The association of HFI with hormonal disturbances in males further supports the endocrine-mediated pathogenesis hypothesis.
PMID:36217295 SUPPORT Human Clinical
"It is most often found in women after menopause. It is also associated with hormonal imbalance, being overweight, history of headaches, and neurocognitive degenerative conditions. Female gender, advanced age, extended estrogen stimulation, and elevated leptin levels may also play a role."
Summarizes the leading etiological theories including estrogen, leptin, and hormonal imbalance for HFI development.
+ 2 more references
Neurological compression from calvarial thickening
Progressive thickening of the frontal bone inner table can lead to compression of underlying brain parenchyma, particularly the frontal lobes. This mechanical compression may result in cerebral atrophy, cognitive impairment, neuropsychiatric symptoms including depression and anxiety, headaches, seizures, and cranial nerve dysfunction affecting olfaction and vision.
Neuron link
Neuron apoptotic process link
Frontal cortex link
Show evidence (3 references)
PMID:27428347 SUPPORT Human Clinical
"In she were performed imaging of the skull where was observed the presence of extensive hyperostosis frontalis interna, cortical atrophy and a left thalamic lacunar infarction."
Imaging findings demonstrate the association between HFI and cortical atrophy in a patient with MSM syndrome.
PMID:25382447 SUPPORT Human Clinical
"In 1928 Stewart and in 1930 Morel added neuropsychiatric symptoms, e.g. depression and dementia, which led to the definition of the Morgagni-Stewart-Morel Syndrome (MSM)."
Establishes the historical association between HFI and neuropsychiatric symptoms including depression and dementia as core features of MSM.
PMID:23284007 SUPPORT Human Clinical
"the severity of our patient's neurological and psychiatric symptoms correlates well with the severity of her hyperostosis frontalis interna and the cortical atrophy."
Demonstrates dose-response relationship between HFI severity and neuropsychiatric symptom severity, supporting mechanical compression.
Hyperprolactinemia-associated endocrine dysfunction
Hyperostosis frontalis interna is strongly associated with acromegaly and hyperprolactinemia, particularly when both conditions coexist. Elevated prolactin levels may contribute to menstrual disturbances, galactorrhea, and hirsutism observed in MSM syndrome. The relationship between HFI and hyperprolactinemia appears to be particularly strong in acromegalic patients.
Mammotroph link
Prolactin secretion link
Anterior pituitary gland link
Show evidence (3 references)
PMID:2349162 SUPPORT Human Clinical
"Acromegalic patients with hyperprolactinaemia also expressed HFI in a higher proportion of individuals than the control group (P = 0.0001)."
Demonstrates a highly significant association between hyperprolactinemia and HFI in acromegalic patients.
PMID:2349162 SUPPORT Human Clinical
"The cause of HFI remains unknown but appears to be strongly associated with acromegaly, particularly in the presence of co-existent hyperprolactinaemia."
Supports the association between HFI and hyperprolactinemia as a contributing pathway in MSM syndrome.
PMID:36223065 PARTIAL Human Clinical
"There was no difference between the HFI positive and negative acromegalic patients in basal GH, IGF-1, and PRL levels, IGF-1 index, diagnosis lag time, and insulin resistance."
A more recent study found no difference in prolactin levels between HFI-positive and HFI-negative acromegalic patients, suggesting the relationship may be indirect.
Increased intracranial pressure from frontal bone expansion
Progressive frontal bone thickening can result in increased intracranial pressure due to reduced intracranial volume and potential obstruction of CSF flow pathways. This increased pressure may contribute to headaches and other neurological symptoms observed in MSM syndrome. The mechanism links the skeletal abnormality (hyperostosis) to neurological manifestations through biomechanical effects.
Regulation of body fluid levels link
Cranial cavity link
Show evidence (2 references)
PMID:36217295 SUPPORT Human Clinical
"It is most often found in women after menopause. It is also associated with hormonal imbalance, being overweight, history of headaches, and neurocognitive degenerative conditions."
Establishes the association between HFI and headaches in affected individuals, supporting the increased ICP hypothesis.
PMID:27428347 SUPPORT Human Clinical
"In she were performed imaging of the skull where was observed the presence of extensive hyperostosis frontalis interna, cortical atrophy and a left thalamic lacunar infarction."
The imaging findings of cortical atrophy in conjunction with extensive HFI support the hypothesis of increased intracranial pressure effects.
⬡

Causal Graph

graph LR
    Hirsutism["Hirsutism"]
    Seizures["Seizures"]
    Vertigo["Vertigo"]
    Obesity["Obesity"]
    Amenorrhea["Amenorrhea"]
    Headache["Headache"]
    Hyperprolactinemia_associated_endocrine_dysfunction["Hyperprolactinemia-associated endocrine dysfunction"]
    Increased_intracranial_pressure_from_frontal_bone_expansion["Increased intracranial pressure from frontal bone expansion"]
    Cognitive_impairment["Cognitive impairment"]
    Neurological_compression_from_calvarial_thickening["Neurological compression from calvarial thickening"]
    Endocrine_mediated_calvarial_bone_overgrowth["Endocrine-mediated calvarial bone overgrowth"]
    Galactorrhea["Galactorrhea"]
    Depression["Depression"]
    Hyperostosis_frontalis_interna["Hyperostosis frontalis interna"]

    Endocrine_mediated_calvarial_bone_overgrowth --> Hyperostosis_frontalis_interna
    Endocrine_mediated_calvarial_bone_overgrowth --> Obesity
    Endocrine_mediated_calvarial_bone_overgrowth --> Increased_intracranial_pressure_from_frontal_bone_expansion
    Neurological_compression_from_calvarial_thickening --> Cognitive_impairment
    Neurological_compression_from_calvarial_thickening --> Depression
    Neurological_compression_from_calvarial_thickening --> Seizures
    Neurological_compression_from_calvarial_thickening --> Increased_intracranial_pressure_from_frontal_bone_expansion
    Neurological_compression_from_calvarial_thickening --> Vertigo
    Hyperprolactinemia_associated_endocrine_dysfunction --> Amenorrhea
    Hyperprolactinemia_associated_endocrine_dysfunction --> Galactorrhea
    Hyperprolactinemia_associated_endocrine_dysfunction --> Hirsutism
    Increased_intracranial_pressure_from_frontal_bone_expansion --> Headache

    style Hirsutism fill:#fef3c7
    style Seizures fill:#fef3c7
    style Vertigo fill:#fef3c7
    style Obesity fill:#fef3c7
    style Amenorrhea fill:#fef3c7
    style Headache fill:#fef3c7
    style Hyperprolactinemia_associated_endocrine_dysfunction fill:#dbeafe
    style Increased_intracranial_pressure_from_frontal_bone_expansion fill:#dbeafe
    style Cognitive_impairment fill:#fef3c7
    style Neurological_compression_from_calvarial_thickening fill:#dbeafe
    style Endocrine_mediated_calvarial_bone_overgrowth fill:#dbeafe
    style Galactorrhea fill:#fef3c7
    style Depression fill:#fef3c7
    style Hyperostosis_frontalis_interna fill:#fef3c7
●

Phenotypes

12
Breast(1) Ear(1) Endocrine(2) Genitourinary(1) Head and Neck(1) Integument(1) Nervous System(4) Growth(1)
Breast 1
Galactorrhea HP_0040284 Galactorrhea (HP:0100829)
Show evidence (1 reference)
PMID:2349162 SUPPORT Human Clinical
"The cause of HFI remains unknown but appears to be strongly associated with acromegaly, particularly in the presence of co-existent hyperprolactinaemia."
Hyperprolactinemia is strongly associated with HFI. Galactorrhea is a direct clinical manifestation of hyperprolactinemia.
Ear 1
Vertigo HP_0040283 Vertigo (HP:0002321)
Show evidence (1 reference)
PMID:27428347 SUPPORT Human Clinical
"A 74 years old female with a history of exposure to wood smoke, vitiligo, type 2 diabetes mellitus, hypertension and cognitive impairment who enters the hospital by malaise, dizziness, anxiety, confusion, disorientation and difficulty walking."
Dizziness documented as part of the clinical presentation in a case of MSM syndrome.
Endocrine 2
Diabetes mellitus HP_0040283 Diabetes mellitus (HP:0000819)
Show evidence (3 references)
PMID:27428347 SUPPORT Human Clinical
"A 74 years old female with a history of exposure to wood smoke, vitiligo, type 2 diabetes mellitus, hypertension and cognitive impairment who enters the hospital by malaise, dizziness, anxiety, confusion, disorientation and difficulty walking."
Type 2 diabetes mellitus is documented as a comorbidity in this MSM syndrome case report.
PMID:27428347 SUPPORT Human Clinical
"During this hospital stay the presence of grade I obesity, hyperglycemia, hypertriglyceridemia and hyperuricemia was documented."
Hyperglycemia and metabolic disturbances are documented features of MSM syndrome.
PMID:23284007 SUPPORT Human Clinical
"Metabolic and endocrine dysfunctions should be interpreted not only as isolated components of the syndrome, but also as the reason behind its pathogenesis."
Metabolic dysfunctions including glucose dysregulation are considered integral components of MSM syndrome.
Diabetes insipidus HP_0040284 Diabetes insipidus (HP:0000873)
Genitourinary 1
Amenorrhea HP_0040283 Amenorrhea (HP:0000141)
Show evidence (1 reference)
PMID:2349162 SUPPORT Human Clinical
"Acromegalic patients with hyperprolactinaemia also expressed HFI in a higher proportion of individuals than the control group (P = 0.0001)."
Hyperprolactinemia is strongly associated with HFI, and amenorrhea is a well-established consequence of hyperprolactinemia.
Head and Neck 1
Hyperostosis frontalis interna HP_0040281 Hyperostosis frontalis interna (HP:0004438)
Show evidence (3 references)
PMID:36484746 SUPPORT Human Clinical
"Hyperostosis frontalis interna was first described in 1719 in association with obesity and hirsutism, forming Morgagni's syndrome."
Confirms hyperostosis frontalis interna as the defining feature of the syndrome, historically described from its first report.
PMID:10407462 SUPPORT Human Clinical
"Hyperostosis frontalis interna (HFI) is manifested by the accretion of bone on the inner table of the frontal bone."
Defines HFI as bone accretion on the inner table of the frontal bone, consistent with the phenotype description.
PMID:36484746 SUPPORT Human Clinical
"The anomaly exclusively involves the inner table and constantly spares the diploe and the external table."
Specifies that HFI exclusively affects the inner table, sparing the diploe and external table.
Integument 1
Hirsutism HP_0040283 Hirsutism (HP:0001007)
Show evidence (2 references)
PMID:36484746 SUPPORT Human Clinical
"Hyperostosis frontalis interna was first described in 1719 in association with obesity and hirsutism, forming Morgagni's syndrome."
Hirsutism was one of the original features described by Morgagni in 1719 alongside HFI and obesity.
PMID:36452994 SUPPORT Human Clinical
"Morgagni-Stewart-Morel (MSM) syndrome is characterized by the thickening of the frontal bone of the skull (hyperostosis frontalis interna) obesity, neurological symptoms, and hypertrichosis."
Hypertrichosis (hirsutism) is listed as a defining feature of MSM syndrome.
Nervous System 4
Headache HP_0040282 Headache (HP:0002315)
Show evidence (2 references)
PMID:36452994 SUPPORT Human Clinical
"We present the case of a 76-year-old patient who complained of confusion, extreme irritability, and headache and was diagnosed with MSM based on examination, imaging, and test results."
Headache is documented as a presenting symptom in this case of MSM syndrome.
PMID:23284007 SUPPORT Human Clinical
"A 75-year-old woman presented with severe frontal headache and a history of psychotic disorders."
Severe frontal headache was the presenting symptom in this case of full-penetrance MSM syndrome.
Seizures HP_0040283 Seizure (HP:0001250)
Show evidence (1 reference)
PMID:16909048 SUPPORT Human Clinical
"They both have suffered from generalized seizures since their early adulthood."
Both monozygotic twins with MSM syndrome had generalized seizures since early adulthood, supporting seizures as a feature of the syndrome.
Cognitive impairment HP_0040283 Cognitive impairment (HP:0100543)
Show evidence (2 references)
PMID:16909048 SUPPORT Human Clinical
"We report two 71-year-old female monozygotic twins presenting with advanced hyperostosis frontalis interna, obesity, shortness and cognitive impairment."
Cognitive impairment is documented in both twins with MSM syndrome.
PMID:27428347 SUPPORT Human Clinical
"A 74 years old female with a history of exposure to wood smoke, vitiligo, type 2 diabetes mellitus, hypertension and cognitive impairment who enters the hospital by malaise, dizziness, anxiety, confusion, disorientation and difficulty walking."
Cognitive impairment is part of the clinical presentation in this case of MSM syndrome.
Depression HP_0040283 Depression (HP:0000716)
Show evidence (2 references)
PMID:25382447 SUPPORT Human Clinical
"In 1928 Stewart and in 1930 Morel added neuropsychiatric symptoms, e.g. depression and dementia, which led to the definition of the Morgagni-Stewart-Morel Syndrome (MSM)."
Depression is one of the classic neuropsychiatric features that helped define MSM syndrome.
PMID:16909048 SUPPORT Human Clinical
"Moreover, the patients showed some additional conditions only occurring in one individual or the other such as migraine, marked recurrent depressive disorder or polyarthrosis."
Recurrent depressive disorder documented in one of the monozygotic twins with MSM syndrome.
Growth 1
Obesity HP_0040282 Obesity (HP:0001513)
Show evidence (3 references)
PMID:16909048 SUPPORT Human Clinical
"We report two 71-year-old female monozygotic twins presenting with advanced hyperostosis frontalis interna, obesity, shortness and cognitive impairment."
Obesity is documented as a core feature in this twin case report of MSM syndrome.
PMID:27428347 SUPPORT Human Clinical
"During this hospital stay the presence of grade I obesity, hyperglycemia, hypertriglyceridemia and hyperuricemia was documented."
Obesity and metabolic disturbances documented in a clinical case of MSM syndrome.
PMID:36452994 SUPPORT Human Clinical
"Morgagni-Stewart-Morel (MSM) syndrome is characterized by the thickening of the frontal bone of the skull (hyperostosis frontalis interna) obesity, neurological symptoms, and hypertrichosis."
Obesity is listed as a defining feature of MSM syndrome.
🧬

Genetic Associations

1
Familial hyperostosis frontalis interna (Susceptibility)
Show evidence (2 references)
PMID:16909048 SUPPORT Human Clinical
"The symptoms common to both twins appear to correspond to the Morgagni-Stewart-Morel syndrome and indicate a genetic basis of this disorder as these features occur in genetically identical patients."
Identical phenotype in monozygotic twins provides strong evidence for a genetic basis of MSM syndrome.
PMID:36223065 SUPPORT Human Clinical
"Various genetic or epigenetic factors may contribute to its etiology."
Supports the hypothesis that genetic or epigenetic factors underlie HFI susceptibility.
💊

Treatments

4
Symptomatic headache management MAXO:0000058
Standard analgesic medications for management of chronic headaches associated with the syndrome.
Show evidence (2 references)
PMID:23284007 SUPPORT Human Clinical
"A 75-year-old woman presented with severe frontal headache and a history of psychotic disorders."
Severe frontal headache is a prominent presenting symptom in MSM syndrome requiring pharmacological management.
PMID:36452994 SUPPORT Human Clinical
"We present the case of a 76-year-old patient who complained of confusion, extreme irritability, and headache and was diagnosed with MSM based on examination, imaging, and test results."
Headache is documented as a presenting complaint requiring symptomatic treatment in MSM.
Antiepileptic therapy MAXO:0000058
Standard antiepileptic medications for management of seizures when present.
Show evidence (1 reference)
PMID:16909048 SUPPORT Human Clinical
"They both have suffered from generalized seizures since their early adulthood."
Generalized seizures from early adulthood in MSM patients require ongoing antiepileptic management.
Multidisciplinary management MAXO:0000950
Comprehensive care targeting the neurological, endocrine, and metabolic components of the syndrome through coordinated multidisciplinary care.
Show evidence (2 references)
PMID:41229651 SUPPORT Human Clinical
"A multidisciplinary approach targeting the neurological, endocrine, and respiratory components led to progressive clinical improvement and a favourable recovery."
Multidisciplinary management targeting multiple organ systems led to favorable outcomes in an acute MSM case.
PMID:41229651 SUPPORT Human Clinical
"Multidisciplinary collaboration is crucial in managing complex cases of Morgagni-Stewart-Morel syndrome, especially in acute settings where diagnosis is challenging."
Authors emphasize the importance of multidisciplinary collaboration for MSM syndrome management.
Genetic counseling MAXO:0000079
Recommended for patients and their families given the evidence for genetic predisposition in the syndrome.
Show evidence (1 reference)
PMID:16909048 SUPPORT Human Clinical
"The symptoms common to both twins appear to correspond to the Morgagni-Stewart-Morel syndrome and indicate a genetic basis of this disorder as these features occur in genetically identical patients."
Evidence for a genetic basis supports the recommendation for genetic counseling in affected families.
🌍

Environmental Factors

1
Prolonged estrogen exposure
Extended exposure to endogenous estrogen, as seen in postmenopausal women with a history of obesity, is hypothesized to contribute to the development of hyperostosis frontalis interna through stimulation of osteoblastic activity in the frontal bone.
Show evidence (3 references)
PMID:10407462 SUPPORT Human Clinical
"It is most commonly found among females and is believed to be associated with prolonged estrogen stimulation"
Large-scale anthropological study supports prolonged estrogen stimulation as a contributing factor to HFI development.
PMID:10407462 SUPPORT Human Clinical
"HFI is associated with age insofar as it is much less frequent in females under 40 years of age."
Age-related increase in HFI frequency is consistent with cumulative estrogen exposure as a risk factor.
PMID:36217295 SUPPORT Human Clinical
"Female gender, advanced age, extended estrogen stimulation, and elevated leptin levels may also play a role."
Identifies extended estrogen stimulation as a potential contributing factor for HFI development.
🔬

Biochemical Markers

2
Growth hormone (Elevated)
Context: Basal plasma growth hormone levels slightly increased with failure to suppress after glucose loading
Show evidence (2 references)
PMID:36223065 PARTIAL Human Clinical
"The frequency of HFI was higher in acromegalic patients than in the controls (22%, 0%, and 2.2%, respectively)."
HFI is significantly more frequent in patients with GH excess (acromegaly), though the study found no direct causal role for GH in HFI etiopathogenesis.
PMID:2349162 SUPPORT Human Clinical
"There was a higher prevalence of HFI in the skull X-rays of the acromegalic cohort (P = 0.0002) when compared to the control group."
Highly significant association between acromegaly (GH excess) and HFI prevalence.
Prolactin (Elevated)
Context: Hyperprolactinemia found in patients with hyperostosis frontalis interna and galactorrhea
Show evidence (2 references)
PMID:2349162 SUPPORT Human Clinical
"Acromegalic patients with hyperprolactinaemia also expressed HFI in a higher proportion of individuals than the control group (P = 0.0001)."
Highly significant association between hyperprolactinemia and HFI in acromegalic patients.
PMID:36223065 PARTIAL Human Clinical
"There was no difference between the HFI positive and negative acromegalic patients in basal GH, IGF-1, and PRL levels, IGF-1 index, diagnosis lag time, and insulin resistance."
While hyperprolactinemia has been historically associated with MSM, this study found no difference in prolactin levels between HFI-positive and HFI-negative acromegalic patients.
🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Morgagni-Stewart-Morel Syndrome:

Paget disease of bone Not Yet Curated MONDO:0005382
Distinguishing Features
  • Paget disease involves both inner and outer tables and diploe with characteristic cotton-wool appearance on imaging, unlike HFI which exclusively affects the inner table.
Show evidence (3 references)
PMID:36484746 SUPPORT Human Clinical
"The main differential diagnosis of cranial hyperostosis is made between meningioma, osteoma, Paget's disease and fibrous dysplasia."
Paget disease is listed as a major differential diagnosis for cranial hyperostosis.
PMID:15228235 SUPPORT Human Clinical
"HFI should be recognized as a benign entity and distinguished from other disorders that involve the frontal skull bone, such as Paget's disease, acromegaly, and malignancy."
Emphasizes the importance of distinguishing HFI from Paget disease and other conditions affecting the frontal skull bone.
PMID:36484746 SUPPORT Human Clinical
"The anomaly exclusively involves the inner table and constantly spares the diploe and the external table."
The key distinguishing feature is that HFI exclusively affects the inner table, while Paget disease involves all layers.
Meningioma Not Yet Curated MONDO:0016642
Distinguishing Features
  • Meningiomas can cause focal hyperostosis but typically present as a mass lesion with contrast enhancement on imaging, unlike the diffuse bilateral inner table thickening of HFI.
Show evidence (1 reference)
PMID:36484746 SUPPORT Human Clinical
"The main differential diagnosis of cranial hyperostosis is made between meningioma, osteoma, Paget's disease and fibrous dysplasia."
Meningioma is listed as a major differential diagnosis for cranial hyperostosis.
Fibrous dysplasia Not Yet Curated MONDO:0000845
Distinguishing Features
  • Fibrous dysplasia involves replacement of normal bone with fibrous tissue and has a ground-glass appearance on imaging, affecting the diploe rather than the inner table exclusively.
Show evidence (1 reference)
PMID:36484746 SUPPORT Human Clinical
"The main differential diagnosis of cranial hyperostosis is made between meningioma, osteoma, Paget's disease and fibrous dysplasia."
Fibrous dysplasia is listed as a major differential diagnosis for cranial hyperostosis.
{ }

Source YAML

click to show 
name: Morgagni-Stewart-Morel Syndrome
creation_date: '2026-02-09T22:41:02Z'
updated_date: '2026-02-14T02:35:30Z'
category: Complex
description: >
  Morgagni-Stewart-Morel syndrome is a rare condition characterized by the triad of
  hyperostosis frontalis interna (thickening of the inner table of the frontal bone),
  obesity, and neuropsychiatric disturbances. Additional features include endocrine
  disorders such as diabetes mellitus, diabetes insipidus, hyperparathyroidism,
  hyperprolactinemia, hirsutism, and menstrual irregularities. The syndrome predominantly
  affects postmenopausal women, with a female-to-male ratio of approximately 9:1.
  The etiology remains incompletely understood but is thought to involve endocrine
  imbalance driven by genetic and environmental factors, with prolonged estrogen
  exposure, elevated leptin levels, and growth hormone dysregulation implicated in
  the pathogenesis of the skull thickening.
disease_term:
  preferred_term: Morgagni-Stewart-Morel syndrome
  term:
    id: MONDO:0007766
    label: Morgagni-Stewart-Morel syndrome
mappings:
  icd10cm_mappings:
  - term:
      id: ICD10CM:M85.2
      label: Hyperostosis of skull
    mapping_predicate: skos:closeMatch
    mapping_source: ICD-10-CM
    mapping_justification: >
      ICD-10-CM M85.2 covers hyperostosis of skull, which encompasses
      the defining feature of Morgagni-Stewart-Morel syndrome (hyperostosis
      frontalis interna). No specific ICD-10 code exists for the full
      syndrome.
    consistency:
    - reference: MONDO
      consistent: MISSING
parents:
- Metabolic bone disease
- Endocrine disorder
synonyms:
- Hyperostosis frontalis interna
- Morgagni syndrome
- Stewart-Morel syndrome
- Metabolic craniopathy
inheritance:
- name: Autosomal dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  penetrance: INCOMPLETE
  expressivity: VARIABLE
  description: >
    Multiple-generation family studies and monozygotic twin concordance suggest
    autosomal dominant inheritance with incomplete penetrance and variable
    expressivity. Hyperostosis frontalis interna has been found in multiple
    generations of affected families, though no case of male-to-male transmission
    has been documented, and X-linked dominant inheritance has not been excluded.
  evidence:
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report two 71-year-old female monozygotic twins presenting with advanced hyperostosis frontalis interna, obesity, shortness and cognitive impairment. They both have suffered from generalized seizures since their early adulthood."
    explanation: Monozygotic twin concordance for MSM syndrome features strongly supports a genetic basis for the disorder.
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms common to both twins appear to correspond to the Morgagni-Stewart-Morel syndrome and indicate a genetic basis of this disorder as these features occur in genetically identical patients."
    explanation: The authors explicitly conclude that the concordance in monozygotic twins indicates a genetic basis for MSM syndrome.
pathophysiology:
- name: Endocrine-mediated calvarial bone overgrowth
  description: >
    The precise pathogenesis of frontal bone thickening remains unclear. Well-supported
    hypotheses include prolonged estrogen exposure stimulating osteoblastic activity
    in the frontal bone inner table (supported by large-scale anthropological studies)
    and elevated leptin levels associated with obesity promoting bone formation. A more
    contested hypothesis involves dysregulated growth hormone secretion from pituitary
    microadenomatosis; however, recent evidence shows no direct causative role for GH
    excess or hyperprolactinemia in HFI etiopathogenesis. The condition predominantly
    affects females and is associated with age, being much less frequent in females
    under 40 years.
  cell_types:
  - preferred_term: Osteoblast
    term:
      id: CL:0000062
      label: osteoblast
  biological_processes:
  - preferred_term: Bone mineralization
    term:
      id: GO:0030282
      label: bone mineralization
  - preferred_term: Osteoblast differentiation
    term:
      id: GO:0001649
      label: osteoblast differentiation
  locations:
  - preferred_term: Frontal bone
    term:
      id: UBERON:0000209
      label: tetrapod frontal bone
  downstream:
  - target: Hyperostosis frontalis interna
  - target: Obesity
  - target: Increased intracranial pressure from frontal bone expansion
  evidence:
  - reference: PMID:10407462
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is most commonly found among females and is believed to be associated with prolonged estrogen stimulation"
    explanation: Establishes the estrogen hypothesis for HFI pathogenesis based on a large-scale anthropological study of over 1,700 skulls.
  - reference: PMID:10407462
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "While its magnitude of manifestation and frequency are much higher in females, HFI is not a purely female phenomenon. Males with hormonal disturbances such as atrophic testis were found to manifest HFI type D."
    explanation: The association of HFI with hormonal disturbances in males further supports the endocrine-mediated pathogenesis hypothesis.
  - reference: PMID:36217295
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is most often found in women after menopause. It is also associated with hormonal imbalance, being overweight, history of headaches, and neurocognitive degenerative conditions. Female gender, advanced age, extended estrogen stimulation, and elevated leptin levels may also play a role."
    explanation: Summarizes the leading etiological theories including estrogen, leptin, and hormonal imbalance for HFI development.
  - reference: PMID:36223065
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the frequency of HFI is 22% in patients with acromegaly, neither excess GH nor hyperprolactinemia plays a role in its etiopathogenesis. Various genetic or epigenetic factors may contribute to its etiology."
    explanation: While HFI is more frequent in acromegaly, this study found no direct role for GH excess or hyperprolactinemia, suggesting genetic/epigenetic factors instead.
  - reference: PMID:23284007
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Endocrine or nutritional disorders may have led to an altered bone metabolism with frontal bone apposition."
    explanation: Supports the concept that endocrine and metabolic dysfunction drives altered bone metabolism leading to frontal hyperostosis.
- name: Neurological compression from calvarial thickening
  description: >
    Progressive thickening of the frontal bone inner table can lead to compression
    of underlying brain parenchyma, particularly the frontal lobes. This mechanical
    compression may result in cerebral atrophy, cognitive impairment,
    neuropsychiatric symptoms including depression and anxiety, headaches,
    seizures, and cranial nerve dysfunction affecting olfaction and vision.
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: Neuron apoptotic process
    term:
      id: GO:0051402
      label: neuron apoptotic process
  locations:
  - preferred_term: Frontal cortex
    term:
      id: UBERON:0001870
      label: frontal cortex
  downstream:
  - target: Cognitive impairment
  - target: Depression
  - target: Seizures
  - target: Increased intracranial pressure from frontal bone expansion
  - target: Vertigo
  evidence:
  - reference: PMID:27428347
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In she were performed imaging of the skull where was observed the presence of extensive hyperostosis frontalis interna, cortical atrophy and a left thalamic lacunar infarction."
    explanation: Imaging findings demonstrate the association between HFI and cortical atrophy in a patient with MSM syndrome.
  - reference: PMID:25382447
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In 1928 Stewart and in 1930 Morel added neuropsychiatric symptoms, e.g. depression and dementia, which led to the definition of the Morgagni-Stewart-Morel Syndrome (MSM)."
    explanation: Establishes the historical association between HFI and neuropsychiatric symptoms including depression and dementia as core features of MSM.
  - reference: PMID:23284007
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the severity of our patient's neurological and psychiatric symptoms correlates well with the severity of her hyperostosis frontalis interna and the cortical atrophy."
    explanation: Demonstrates dose-response relationship between HFI severity and neuropsychiatric symptom severity, supporting mechanical compression.
- name: Hyperprolactinemia-associated endocrine dysfunction
  description: >
    Hyperostosis frontalis interna is strongly associated with acromegaly and
    hyperprolactinemia, particularly when both conditions coexist. Elevated
    prolactin levels may contribute to menstrual disturbances, galactorrhea,
    and hirsutism observed in MSM syndrome. The relationship between HFI
    and hyperprolactinemia appears to be particularly strong in acromegalic
    patients.
  cell_types:
  - preferred_term: Mammotroph
    term:
      id: CL:0002311
      label: mammotroph
  biological_processes:
  - preferred_term: Prolactin secretion
    term:
      id: GO:0070460
      label: prolactin secretion
  locations:
  - preferred_term: Anterior pituitary gland
    term:
      id: UBERON:0002196
      label: adenohypophysis
  downstream:
  - target: Amenorrhea
  - target: Galactorrhea
  - target: Hirsutism
  evidence:
  - reference: PMID:2349162
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Acromegalic patients with hyperprolactinaemia also expressed HFI in a higher proportion of individuals than the control group (P = 0.0001)."
    explanation: Demonstrates a highly significant association between hyperprolactinemia and HFI in acromegalic patients.
  - reference: PMID:2349162
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The cause of HFI remains unknown but appears to be strongly associated with acromegaly, particularly in the presence of co-existent hyperprolactinaemia."
    explanation: Supports the association between HFI and hyperprolactinemia as a contributing pathway in MSM syndrome.
  - reference: PMID:36223065
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "There was no difference between the HFI positive and negative acromegalic patients in basal GH, IGF-1, and PRL levels, IGF-1 index, diagnosis lag time, and insulin resistance."
    explanation: A more recent study found no difference in prolactin levels between HFI-positive and HFI-negative acromegalic patients, suggesting the relationship may be indirect.
- name: Increased intracranial pressure from frontal bone expansion
  description: >
    Progressive frontal bone thickening can result in increased intracranial pressure
    due to reduced intracranial volume and potential obstruction of CSF flow pathways.
    This increased pressure may contribute to headaches and other neurological symptoms
    observed in MSM syndrome. The mechanism links the skeletal abnormality (hyperostosis)
    to neurological manifestations through biomechanical effects.
  biological_processes:
  - preferred_term: Regulation of body fluid levels
    term:
      id: GO:0050878
      label: regulation of body fluid levels
  locations:
  - preferred_term: Cranial cavity
    term:
      id: UBERON:0003128
      label: cranial cavity
  downstream:
  - target: Headache
  evidence:
  - reference: PMID:36217295
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is most often found in women after menopause. It is also associated with hormonal imbalance, being overweight, history of headaches, and neurocognitive degenerative conditions."
    explanation: Establishes the association between HFI and headaches in affected individuals, supporting the increased ICP hypothesis.
  - reference: PMID:27428347
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In she were performed imaging of the skull where was observed the presence of extensive hyperostosis frontalis interna, cortical atrophy and a left thalamic lacunar infarction."
    explanation: The imaging findings of cortical atrophy in conjunction with extensive HFI support the hypothesis of increased intracranial pressure effects.
phenotypes:
- name: Hyperostosis frontalis interna
  description: >
    Bilateral, irregular thickening of the inner table of the frontal bone,
    typically sparing the midline at the superior sagittal sinus. This is the
    defining radiological feature, usually discovered incidentally on skull
    X-ray, CT, or MRI.
  frequency: HP_0040281
  diagnostic: true
  category: Skeletal
  phenotype_term:
    preferred_term: Hyperostosis frontalis interna
    term:
      id: HP:0004438
      label: Hyperostosis frontalis interna
  evidence:
  - reference: PMID:36484746
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperostosis frontalis interna was first described in 1719 in association with obesity and hirsutism, forming Morgagni's syndrome."
    explanation: Confirms hyperostosis frontalis interna as the defining feature of the syndrome, historically described from its first report.
  - reference: PMID:10407462
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperostosis frontalis interna (HFI) is manifested by the accretion of bone on the inner table of the frontal bone."
    explanation: Defines HFI as bone accretion on the inner table of the frontal bone, consistent with the phenotype description.
  - reference: PMID:36484746
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The anomaly exclusively involves the inner table and constantly spares the diploe and the external table."
    explanation: Specifies that HFI exclusively affects the inner table, sparing the diploe and external table.
- name: Obesity
  description: >
    Central obesity is a cardinal feature, present in the majority of affected
    individuals. It may be related to endocrine dysregulation including leptin
    resistance and growth hormone abnormalities.
  frequency: HP_0040282
  category: Metabolic
  phenotype_term:
    preferred_term: Obesity
    term:
      id: HP:0001513
      label: Obesity
  evidence:
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report two 71-year-old female monozygotic twins presenting with advanced hyperostosis frontalis interna, obesity, shortness and cognitive impairment."
    explanation: Obesity is documented as a core feature in this twin case report of MSM syndrome.
  - reference: PMID:27428347
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "During this hospital stay the presence of grade I obesity, hyperglycemia, hypertriglyceridemia and hyperuricemia was documented."
    explanation: Obesity and metabolic disturbances documented in a clinical case of MSM syndrome.
  - reference: PMID:36452994
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Morgagni-Stewart-Morel (MSM) syndrome is characterized by the thickening of the frontal bone of the skull (hyperostosis frontalis interna) obesity, neurological symptoms, and hypertrichosis."
    explanation: Obesity is listed as a defining feature of MSM syndrome.
- name: Headache
  description: >
    Chronic headaches are a common presenting symptom, potentially related to
    increased intracranial pressure from calvarial thickening or direct
    compression effects.
  frequency: HP_0040282
  category: Neurological
  phenotype_term:
    preferred_term: Headache
    term:
      id: HP:0002315
      label: Headache
  evidence:
  - reference: PMID:36452994
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present the case of a 76-year-old patient who complained of confusion, extreme irritability, and headache and was diagnosed with MSM based on examination, imaging, and test results."
    explanation: Headache is documented as a presenting symptom in this case of MSM syndrome.
  - reference: PMID:23284007
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 75-year-old woman presented with severe frontal headache and a history of psychotic disorders."
    explanation: Severe frontal headache was the presenting symptom in this case of full-penetrance MSM syndrome.
- name: Seizures
  description: >
    Generalized seizures may occur, potentially related to frontal lobe
    compression from the hyperostotic bone. Seizures have been reported
    since early adulthood in some patients.
  frequency: HP_0040283
  category: Neurological
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They both have suffered from generalized seizures since their early adulthood."
    explanation: Both monozygotic twins with MSM syndrome had generalized seizures since early adulthood, supporting seizures as a feature of the syndrome.
- name: Cognitive impairment
  description: >
    Progressive cognitive decline may develop, attributed to frontal lobe
    compression and atrophy from the expanding inner table of the skull.
  frequency: HP_0040283
  category: Neurological
  phenotype_term:
    preferred_term: Cognitive impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
  evidence:
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report two 71-year-old female monozygotic twins presenting with advanced hyperostosis frontalis interna, obesity, shortness and cognitive impairment."
    explanation: Cognitive impairment is documented in both twins with MSM syndrome.
  - reference: PMID:27428347
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 74 years old female with a history of exposure to wood smoke, vitiligo, type 2 diabetes mellitus, hypertension and cognitive impairment who enters the hospital by malaise, dizziness, anxiety, confusion, disorientation and difficulty walking."
    explanation: Cognitive impairment is part of the clinical presentation in this case of MSM syndrome.
- name: Depression
  description: >
    Depressive symptoms are frequently reported and may be related to frontal
    lobe dysfunction or the broader neuropsychiatric component of the syndrome.
  frequency: HP_0040283
  category: Psychiatric
  phenotype_term:
    preferred_term: Depression
    term:
      id: HP:0000716
      label: Depression
  evidence:
  - reference: PMID:25382447
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In 1928 Stewart and in 1930 Morel added neuropsychiatric symptoms, e.g. depression and dementia, which led to the definition of the Morgagni-Stewart-Morel Syndrome (MSM)."
    explanation: Depression is one of the classic neuropsychiatric features that helped define MSM syndrome.
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Moreover, the patients showed some additional conditions only occurring in one individual or the other such as migraine, marked recurrent depressive disorder or polyarthrosis."
    explanation: Recurrent depressive disorder documented in one of the monozygotic twins with MSM syndrome.
- name: Hirsutism
  description: >
    Excess body hair growth in a male pattern distribution in affected females,
    related to the virilism component of the syndrome and potentially linked
    to hyperprolactinemia or androgen dysregulation.
  frequency: HP_0040283
  category: Dermatological
  phenotype_term:
    preferred_term: Hirsutism
    term:
      id: HP:0001007
      label: Hirsutism
  evidence:
  - reference: PMID:36484746
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperostosis frontalis interna was first described in 1719 in association with obesity and hirsutism, forming Morgagni's syndrome."
    explanation: Hirsutism was one of the original features described by Morgagni in 1719 alongside HFI and obesity.
  - reference: PMID:36452994
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Morgagni-Stewart-Morel (MSM) syndrome is characterized by the thickening of the frontal bone of the skull (hyperostosis frontalis interna) obesity, neurological symptoms, and hypertrichosis."
    explanation: Hypertrichosis (hirsutism) is listed as a defining feature of MSM syndrome.
- name: Vertigo
  description: >
    Dizziness and vertigo are reported neurological symptoms, potentially
    related to cranial nerve involvement or intracranial pressure changes.
  frequency: HP_0040283
  category: Neurological
  phenotype_term:
    preferred_term: Vertigo
    term:
      id: HP:0002321
      label: Vertigo
  evidence:
  - reference: PMID:27428347
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 74 years old female with a history of exposure to wood smoke, vitiligo, type 2 diabetes mellitus, hypertension and cognitive impairment who enters the hospital by malaise, dizziness, anxiety, confusion, disorientation and difficulty walking."
    explanation: Dizziness documented as part of the clinical presentation in a case of MSM syndrome.
- name: Amenorrhea
  description: >
    Menstrual disturbances including amenorrhea are part of the endocrine
    manifestations of the syndrome, potentially linked to hyperprolactinemia
    or hypothalamic-pituitary dysfunction.
  frequency: HP_0040283
  category: Endocrine
  phenotype_term:
    preferred_term: Amenorrhea
    term:
      id: HP:0000141
      label: Amenorrhea
  evidence:
  - reference: PMID:2349162
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Acromegalic patients with hyperprolactinaemia also expressed HFI in a higher proportion of individuals than the control group (P = 0.0001)."
    explanation: Hyperprolactinemia is strongly associated with HFI, and amenorrhea is a well-established consequence of hyperprolactinemia.
- name: Galactorrhea
  description: >
    Inappropriate lactation related to hyperprolactinemia, which has been
    found in a significant proportion of patients with hyperostosis frontalis
    interna.
  frequency: HP_0040284
  category: Endocrine
  phenotype_term:
    preferred_term: Galactorrhea
    term:
      id: HP:0100829
      label: Galactorrhea
  evidence:
  - reference: PMID:2349162
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The cause of HFI remains unknown but appears to be strongly associated with acromegaly, particularly in the presence of co-existent hyperprolactinaemia."
    explanation: Hyperprolactinemia is strongly associated with HFI. Galactorrhea is a direct clinical manifestation of hyperprolactinemia.
- name: Diabetes mellitus
  description: >
    Type 2 diabetes mellitus and insulin resistance are frequent metabolic
    manifestations of the syndrome, likely related to the underlying endocrine
    dysregulation and obesity.
  frequency: HP_0040283
  category: Endocrine
  phenotype_term:
    preferred_term: Diabetes mellitus
    term:
      id: HP:0000819
      label: Diabetes mellitus
  evidence:
  - reference: PMID:27428347
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 74 years old female with a history of exposure to wood smoke, vitiligo, type 2 diabetes mellitus, hypertension and cognitive impairment who enters the hospital by malaise, dizziness, anxiety, confusion, disorientation and difficulty walking."
    explanation: Type 2 diabetes mellitus is documented as a comorbidity in this MSM syndrome case report.
  - reference: PMID:27428347
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "During this hospital stay the presence of grade I obesity, hyperglycemia, hypertriglyceridemia and hyperuricemia was documented."
    explanation: Hyperglycemia and metabolic disturbances are documented features of MSM syndrome.
  - reference: PMID:23284007
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Metabolic and endocrine dysfunctions should be interpreted not only as isolated components of the syndrome, but also as the reason behind its pathogenesis."
    explanation: Metabolic dysfunctions including glucose dysregulation are considered integral components of MSM syndrome.
- name: Diabetes insipidus
  description: >
    Diabetes insipidus has been reported as an endocrine manifestation in some
    patients, potentially related to hypothalamic-pituitary dysfunction.
  frequency: HP_0040284
  category: Endocrine
  phenotype_term:
    preferred_term: Diabetes insipidus
    term:
      id: HP:0000873
      label: Diabetes insipidus
biochemical:
- name: Growth hormone
  presence: Elevated
  context: Basal plasma growth hormone levels slightly increased with failure to suppress after glucose loading
  biomarker_term:
    preferred_term: Growth hormone
    term:
      id: NCIT:C2288
      label: Somatotropin
  evidence:
  - reference: PMID:36223065
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "The frequency of HFI was higher in acromegalic patients than in the controls (22%, 0%, and 2.2%, respectively)."
    explanation: HFI is significantly more frequent in patients with GH excess (acromegaly), though the study found no direct causal role for GH in HFI etiopathogenesis.
  - reference: PMID:2349162
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was a higher prevalence of HFI in the skull X-rays of the acromegalic cohort (P = 0.0002) when compared to the control group."
    explanation: Highly significant association between acromegaly (GH excess) and HFI prevalence.
- name: Prolactin
  presence: Elevated
  context: Hyperprolactinemia found in patients with hyperostosis frontalis interna and galactorrhea
  biomarker_term:
    preferred_term: Prolactin
    term:
      id: NCIT:C778
      label: Prolactin
  evidence:
  - reference: PMID:2349162
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Acromegalic patients with hyperprolactinaemia also expressed HFI in a higher proportion of individuals than the control group (P = 0.0001)."
    explanation: Highly significant association between hyperprolactinemia and HFI in acromegalic patients.
  - reference: PMID:36223065
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "There was no difference between the HFI positive and negative acromegalic patients in basal GH, IGF-1, and PRL levels, IGF-1 index, diagnosis lag time, and insulin resistance."
    explanation: While hyperprolactinemia has been historically associated with MSM, this study found no difference in prolactin levels between HFI-positive and HFI-negative acromegalic patients.
genetic:
- name: Familial hyperostosis frontalis interna
  association: Susceptibility
  notes: >
    Familial aggregation documented across multiple generations with predominantly
    female involvement. Monozygotic twin concordance supports a genetic basis.
    The specific genes involved have not been identified. Inheritance pattern
    is consistent with autosomal dominant with sex-influenced expression, though
    X-linked dominant inheritance cannot be excluded.
  evidence:
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms common to both twins appear to correspond to the Morgagni-Stewart-Morel syndrome and indicate a genetic basis of this disorder as these features occur in genetically identical patients."
    explanation: Identical phenotype in monozygotic twins provides strong evidence for a genetic basis of MSM syndrome.
  - reference: PMID:36223065
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Various genetic or epigenetic factors may contribute to its etiology."
    explanation: Supports the hypothesis that genetic or epigenetic factors underlie HFI susceptibility.
environmental:
- name: Prolonged estrogen exposure
  description: >
    Extended exposure to endogenous estrogen, as seen in postmenopausal women
    with a history of obesity, is hypothesized to contribute to the development
    of hyperostosis frontalis interna through stimulation of osteoblastic
    activity in the frontal bone.
  exposure_term:
    preferred_term: exposure to estrogens
    term:
      id: ECTO:9000010
      label: exposure to estrogens
  evidence:
  - reference: PMID:10407462
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is most commonly found among females and is believed to be associated with prolonged estrogen stimulation"
    explanation: Large-scale anthropological study supports prolonged estrogen stimulation as a contributing factor to HFI development.
  - reference: PMID:10407462
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HFI is associated with age insofar as it is much less frequent in females under 40 years of age."
    explanation: Age-related increase in HFI frequency is consistent with cumulative estrogen exposure as a risk factor.
  - reference: PMID:36217295
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Female gender, advanced age, extended estrogen stimulation, and elevated leptin levels may also play a role."
    explanation: Identifies extended estrogen stimulation as a potential contributing factor for HFI development.
treatments:
- name: Symptomatic headache management
  description: >
    Standard analgesic medications for management of chronic headaches
    associated with the syndrome.
  treatment_term:
    preferred_term: Symptomatic headache management
    term:
      id: MAXO:0000058
      label: pharmacotherapy
  evidence:
  - reference: PMID:23284007
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 75-year-old woman presented with severe frontal headache and a history of psychotic disorders."
    explanation: Severe frontal headache is a prominent presenting symptom in MSM syndrome requiring pharmacological management.
  - reference: PMID:36452994
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present the case of a 76-year-old patient who complained of confusion, extreme irritability, and headache and was diagnosed with MSM based on examination, imaging, and test results."
    explanation: Headache is documented as a presenting complaint requiring symptomatic treatment in MSM.
- name: Antiepileptic therapy
  description: >
    Standard antiepileptic medications for management of seizures when present.
  treatment_term:
    preferred_term: Antiepileptic therapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
  evidence:
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They both have suffered from generalized seizures since their early adulthood."
    explanation: Generalized seizures from early adulthood in MSM patients require ongoing antiepileptic management.
- name: Multidisciplinary management
  description: >
    Comprehensive care targeting the neurological, endocrine, and metabolic
    components of the syndrome through coordinated multidisciplinary care.
  treatment_term:
    preferred_term: Multidisciplinary management
    term:
      id: MAXO:0000950
      label: supportive care
  evidence:
  - reference: PMID:41229651
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A multidisciplinary approach targeting the neurological, endocrine, and respiratory components led to progressive clinical improvement and a favourable recovery."
    explanation: Multidisciplinary management targeting multiple organ systems led to favorable outcomes in an acute MSM case.
  - reference: PMID:41229651
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Multidisciplinary collaboration is crucial in managing complex cases of Morgagni-Stewart-Morel syndrome, especially in acute settings where diagnosis is challenging."
    explanation: Authors emphasize the importance of multidisciplinary collaboration for MSM syndrome management.
- name: Genetic counseling
  description: >
    Recommended for patients and their families given the evidence for
    genetic predisposition in the syndrome.
  treatment_term:
    preferred_term: Genetic counseling
    term:
      id: MAXO:0000079
      label: genetic counseling
  evidence:
  - reference: PMID:16909048
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The symptoms common to both twins appear to correspond to the Morgagni-Stewart-Morel syndrome and indicate a genetic basis of this disorder as these features occur in genetically identical patients."
    explanation: Evidence for a genetic basis supports the recommendation for genetic counseling in affected families.
prevalence:
- population: General population (hyperostosis frontalis interna)
  percentage: 2.5
  notes: >
    Hyperostosis frontalis interna is found in approximately 2.5% of the general
    population, though full Morgagni-Stewart-Morel syndrome with the complete
    triad is much rarer. The condition is approximately 9 times more common
    in females than males and increases in frequency with age.
  evidence:
  - reference: PMID:36223065
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The frequency of HFI was higher in acromegalic patients than in the controls (22%, 0%, and 2.2%, respectively)."
    explanation: The 2.2% frequency in healthy controls is consistent with the reported general population prevalence of approximately 2.5%.
  - reference: PMID:15228235
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperostosis frontalis interna (HFI) has been reported in high frequency among post-menopausal elderly women."
    explanation: Supports the observation that HFI is relatively common particularly among postmenopausal women.
differential_diagnoses:
- name: Paget disease of bone
  disease_term:
    preferred_term: bone Paget disease
    term:
      id: MONDO:0005382
      label: bone Paget disease
  distinguishing_features:
  - Paget disease involves both inner and outer tables and diploe with characteristic cotton-wool appearance on imaging, unlike HFI which exclusively affects the inner table.
  evidence:
  - reference: PMID:36484746
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main differential diagnosis of cranial hyperostosis is made between meningioma, osteoma, Paget's disease and fibrous dysplasia."
    explanation: Paget disease is listed as a major differential diagnosis for cranial hyperostosis.
  - reference: PMID:15228235
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HFI should be recognized as a benign entity and distinguished from other disorders that involve the frontal skull bone, such as Paget's disease, acromegaly, and malignancy."
    explanation: Emphasizes the importance of distinguishing HFI from Paget disease and other conditions affecting the frontal skull bone.
  - reference: PMID:36484746
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The anomaly exclusively involves the inner table and constantly spares the diploe and the external table."
    explanation: The key distinguishing feature is that HFI exclusively affects the inner table, while Paget disease involves all layers.
- name: Meningioma
  disease_term:
    preferred_term: meningioma
    term:
      id: MONDO:0016642
      label: meningioma
  distinguishing_features:
  - Meningiomas can cause focal hyperostosis but typically present as a mass lesion with contrast enhancement on imaging, unlike the diffuse bilateral inner table thickening of HFI.
  evidence:
  - reference: PMID:36484746
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main differential diagnosis of cranial hyperostosis is made between meningioma, osteoma, Paget's disease and fibrous dysplasia."
    explanation: Meningioma is listed as a major differential diagnosis for cranial hyperostosis.
- name: Fibrous dysplasia
  disease_term:
    preferred_term: fibrous dysplasia
    term:
      id: MONDO:0000845
      label: fibrous dysplasia
  distinguishing_features:
  - Fibrous dysplasia involves replacement of normal bone with fibrous tissue and has a ground-glass appearance on imaging, affecting the diploe rather than the inner table exclusively.
  evidence:
  - reference: PMID:36484746
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main differential diagnosis of cranial hyperostosis is made between meningioma, osteoma, Paget's disease and fibrous dysplasia."
    explanation: Fibrous dysplasia is listed as a major differential diagnosis for cranial hyperostosis.
notes: >
  Morgagni-Stewart-Morel syndrome was first described by Giovanni Battista Morgagni
  in 1719 in an obese female with hirsutism found to have frontal hyperostosis at
  autopsy. Stewart reported three autopsy cases in 1928, and Morel described the
  first living case in 1930. The syndrome remains poorly understood, with debate
  about whether it represents a distinct entity or a syndrome complex. Diagnosis
  is based on the radiological finding of hyperostosis frontalis interna combined
  with obesity and neuropsychiatric features. There is ongoing debate about the
  existence of the syndrome as a unified entity given the high prevalence of HFI
  in the general population. A high prevalence and a lack of studies demonstrating
  a strong correlation between the different signs currently question the existence
  of the syndrome as a discrete entity.