Conditions with similar clinical presentations that must be differentiated from Semicircular Canal Dehiscence Syndrome:
Disease Pathophysiology Research Report Target Disease - Disease Name: Semicircular Canal Dehiscence Syndrome (typically superior SCDS) - MONDO ID: not firmly established (entity often covered under third-window syndromes) - Category: Structural
Pathophysiology Description Core concept: A dehiscence (or extreme thinning) of otic capsule bone over a semicircular canal creates a pathological “third mobile window,” which lowers impedance on the vestibular side of the inner ear and shunts acoustic and pressure energy away from the cochlea toward the dehiscence. This redistributes fluid pressures, alters cochlear and vestibular mechanics, and produces the characteristic combination of low-frequency air–bone gaps (pseudoconductive hearing loss), supranormal bone conduction, and sound/pressure-induced vestibular symptoms (Tullio/Hennebert signs). Mechanistically, to generate conductive hearing loss the third window must be on the scala vestibuli side; patching/plugging the dehiscence can resolve the air–bone gap (mechanistic proof) (Apr 2008, Otology & Neurotology; https://doi.org/10.1097/mao.0b013e318161ab24) (merchant2008conductivehearingloss pages 4-5).
Hydromechanics and vestibular activation: The third window introduces a low-impedance pathway; “a third window will introduce a low mechanical impedance,” shunting sound/pressure, generating large transmembrane pressure gradients and traveling waves in the membranous labyrinth, with outbound flow at the dehiscence balancing inflow at the oval window (Aug 2020, Frontiers in Neurology; https://doi.org/10.3389/fneur.2020.00891) (iversen2020biomechanicsofthird pages 6-7). These waves drive hair-bundle vibration at stimulus frequency (phase-locked irregular afferent firing) and, via nonlinear fluid interactions, endolymph pumping that deflects the cupula (sustained firing in regular afferents). Plugging abolishes these phase-locked responses, consistent with mechanical origin (iversen2020biomechanicsofthird pages 6-7).
Histopathology and anatomy: Temporal bone histology from a clinically diagnosed SCDS case showed a focal bony defect (1.4 × 0.6 mm) with dura directly contacting the endosteum and membranous duct at the defect; notably, “No osteoclastic process was evident within the otic capsule,” and sensory epithelia were preserved without hydrops—supporting a developmental thin-bone predisposition with trauma trigger (Jan 2012, Annals of Otology, Rhinology & Laryngology; https://doi.org/10.1177/000348941212100102) (teixido2012histopathologyofthe pages 1-2).
Bone biology/remodeling: The otic capsule exhibits unique bone physiology with greatly suppressed remodeling. Osteoprotegerin (OPG; TNFRSF11B) is expressed in the inner ear and “may inhibit bone remodeling in the otic capsule,” providing a molecular explanation for its quiescent remodeling state (Jan 2005, The Laryngoscope; https://doi.org/10.1097/01.mlg.0000150702.28451.35) (tikka2023investigationofserum pages 6-6). In a 2023 gerbil SSCD model, fenestrations of the superior canal produced reversible diagnostic features—worsened low-frequency ABR thresholds (proxy for pseudoconductive hearing loss) and increased cVEMP amplitudes with low thresholds—and healed by osteoneogenesis that “resurfac[es] the SSCD without obliteration,” returning electrophysiology toward baseline (Jan 2023, Frontiers in Neurology; https://doi.org/10.3389/fneur.2022.1035478) (wackym2023newmodelof pages 1-2, wackym2023newmodelof pages 14-15). Clinical biochemical work has explored calcium/vitamin D and bone turnover markers in SSCD patients, aligning SSCD with otic capsule bone metabolism hypotheses (Jan 2023, Journal of Otology; https://doi.org/10.1016/j.joto.2022.12.005) (tikka2023investigationofserum pages 6-6).
Diagnostic correlations: Third-window mechanics predict low-frequency air–bone gaps with normal tympanometry, improved bone conduction thresholds, and characteristically low-threshold/high-amplitude VEMPs; surgical repair normalizes measures such as SP/AP ratios on ECoG and resolves the air–bone gap in many cases (merchant2008conductivehearingloss pages 4-5, iversen2020biomechanicsofthird pages 6-7). Contemporary clinical/biomechanical overviews and editorials emphasize that SSCD is the most common third-window disorder and summarize consistent VEMP and vestibulo-ocular reflex findings (Jun 2021, Frontiers in Neurology; https://doi.org/10.3389/fneur.2021.704095) (wackym2021editorialthirdwindow pages 3-4).
Recent developments and latest research (prioritized) - Reversible animal model (2023): Surgical SSCD in gerbils demonstrated (a) low-frequency ABR threshold worsening, (b) increased cVEMP amplitudes/low thresholds, and (c) spontaneous reversal associated with osteoneogenesis and resurfacing of the dehiscence, with many measures returning toward baseline (Jan 2023; Frontiers in Neurology) (wackym2023newmodelof pages 1-2, wackym2023newmodelof pages 14-15). - Biochemical context (2023): Case–control work investigated serum calcium and vitamin D in SSCD, referencing bone turnover markers (alkaline phosphatase, bone alkaline phosphatase, osteocalcin) and literature on osteoclastic activity in temporal bone, suggesting systemic mineral metabolism may interact with local otic capsule biology (Jan 2023; Journal of Otology) (tikka2023investigationofserum pages 6-6). - Mechanistic synthesis: Biomechanical reviews consolidate the role of pressure-driven flows, near-incompressible lymphs, and resultant traveling waves/cupular deflection in third-window states, supporting the diagnostic signatures and explaining symptom triggers (Aug 2020; Frontiers in Neurology) (iversen2020biomechanicsofthird pages 6-7).
Current applications and real-world implementations - Clinical diagnostics: High-resolution temporal bone CT to identify dehiscence; audiometry demonstrating low-frequency air–bone gaps with normal middle-ear tests; VEMPs with reduced thresholds and increased amplitudes; ECoG SP/AP ratio elevation with normalization post-plugging (merchant2008conductivehearingloss pages 4-5, iversen2020biomechanicsofthird pages 6-7, wackym2021editorialthirdwindow pages 3-4). - Surgical repair: Middle cranial fossa or transmastoid canal plugging/resurfacing to eliminate the third window, with resolution of the air–bone gap and improvement of sound/pressure-induced vertigo in many patients, consistent with mechanical mechanism (merchant2008conductivehearingloss pages 4-5, iversen2020biomechanicsofthird pages 6-7). - Emerging models: The 2023 gerbil model offers a platform for testing molecular and biomechanical interventions, showing osteoneogenesis-mediated resurfacing without canal obliteration (wackym2023newmodelof pages 1-2, wackym2023newmodelof pages 14-15).
Expert opinions and authoritative analyses - “A third window will introduce a low mechanical impedance,” shunting energy and generating pressure gradients/waves that activate vestibular afferents; plugging abolishes phase-locked responses—biomechanical proof linking lesion to physiology (Aug 2020; Frontiers in Neurology) (iversen2020biomechanicsofthird pages 6-7). - “To produce a conductive hearing loss the third window must be on the scala vestibuli side,” and “patching/plugging the dehiscence resolves the air–bone gap” (Apr 2008; Otology & Neurotology) (merchant2008conductivehearingloss pages 4-5). - “No osteoclastic process was evident within the otic capsule” in a histopathologically verified clinical SCDS case, consistent with a thin-bone predisposition and trauma-trigger model (Jan 2012; Ann Otol Rhinol Laryngol) (teixido2012histopathologyofthe pages 1-2). - SSCD is the most common third mobile window; editorials summarize diagnostic and QOL impacts and emphasize specific biomarkers such as cochlin-tomoprotein under evaluation (Jun 2021; Frontiers in Neurology) (wackym2021editorialthirdwindow pages 3-4).
Relevant statistics and data - Audiometry: Third-window lesions (including SSCD) typically cause low- to mid-frequency air–bone gaps up to ~2 kHz with improved bone conduction and normal middle-ear measures; correction after plugging confirms causality (Apr 2008; Otology & Neurotology) (merchant2008conductivehearingloss pages 4-5). - VEMPs: Abnormally low thresholds and high amplitudes are characteristic of SSCD and reverse after repair; animal model shows cVEMP amplitude increases with larger fenestrations and returns toward baseline with resurfacing (Jan 2023; Frontiers in Neurology) (wackym2023newmodelof pages 1-2, wackym2023newmodelof pages 14-15, iversen2020biomechanicsofthird pages 6-7). - Histology: Clinical SCDS case with 1.4 × 0.6 mm defect; dura contacting membranous duct; no osteoclasts observed (Jan 2012; Ann Otol Rhinol Laryngol) (teixido2012histopathologyofthe pages 1-2). - Biochemistry: Case–control exploration of serum calcium and vitamin D in SSCD; references to bone turnover markers and literature on temporal bone osteoclastic activity (Jan 2023; Journal of Otology) (tikka2023investigationofserum pages 6-6).
Evidence summary table | Citation (authors, year) | Publication date | Journal | URL | Focus (mechanism / diagnostic) | Core finding (1–2 sentences) | |---|---|---|---|---|---| | Wackym PA et al., 2023 | Jan 2023 | Frontiers in Neurology | https://doi.org/10.3389/fneur.2022.1035478 | Animal model / mechanism & diagnostics | Gerbil SSCD model produced reversible pseudoconductive hearing loss (worse low-frequency ABR) and increased cVEMP amplitudes/low thresholds; micro-CT and histology show bone resurfacing (osteoneogenesis) with recovery of electrophysiologic measures (wackym2023newmodelof pages 1-2, wackym2023newmodelof pages 14-15). | | Iversen MM & Rabbitt RD, 2020 | Aug 2020 | Frontiers in Neurology | https://doi.org/10.3389/fneur.2020.00891 | Biomechanics / mechanism | Detailed biomechanical account of third-window hydromechanics: dehiscence introduces a low-impedance pathway that shunts sound/pressure, generates transmembrane pressure gradients and traveling waves that activate canal and utricular afferents, explaining VEMP and vertigo phenomena (iversen2020biomechanicsofthird pages 6-7). | | Merchant SN & Rosowski JJ, 2008 | Apr 2008 | Otology & Neurotology | https://doi.org/10.1097/mao.0b013e318161ab24 | Mechanism / clinical audiology | Seminal description of third-window effects: vestibular-side dehiscence lowers impedance, producing low-frequency air–bone gaps and enhanced bone conduction (pseudoconductive hearing loss), with resolution after surgical patching/plugging confirming mechanism (merchant2008conductivehearingloss pages 4-5). | | Chien W et al., 2007 | Feb 2007 | Otology & Neurotology | https://doi.org/10.1097/01.mao.0000244370.47320.9a | Human ear mechanics / measurements | Experimental measurements show that superior canal dehiscence behaves as a third window altering middle/inner ear mechanics, redistributing pressure and explaining clinical audiometric patterns and vestibular responses associated with SSCD (supported by biomechanical reviews) (iversen2020biomechanicsofthird pages 6-7). | | Teixidó M et al., 2012 | Jan 2012 | Annals of Otology, Rhinology & Laryngology | https://doi.org/10.1177/000348941212100102 | Histopathology / anatomy | Temporal bone histology of a clinical SSCD case showed a focal bony dehiscence with dura contacting the membranous duct; no clear osteoclastic resorption was seen, supporting thin/developmental bone predisposition and trauma-trigger hypotheses (teixido2012histopathologyofthe pages 1-2). | | Tikka T et al., 2023 | Jan 2023 | Journal of Otology | https://doi.org/10.1016/j.joto.2022.12.005 | Bone biology / clinical biochemistry | Case–control study linking SSCD with investigations of serum calcium and vitamin D; places SSCD in context of otic capsule bone metabolism and suggests roles for calcium/Vit D pathways and osteoclastic activity hypotheses in dehiscence etiology (tikka2023investigationofserum pages 6-6). |
Table: Concise summary of foundational and recent papers on superior semicircular canal dehiscence (SCDS)/third-window pathophysiology, showing publication details, URLs, focus, and 1–2 sentence core findings with supporting context citations.
Structured Annotations Key molecular players (HGNC) and related entities - TNFRSF11B (OPG; HGNC:11909): Secreted decoy receptor inhibiting RANKL; “may inhibit bone remodeling in the otic capsule,” supporting the quiescent remodeling milieu and the biology of thin bone versus active resorption in SCDS (tikka2023investigationofserum pages 6-6). - Bone turnover markers referenced clinically: alkaline phosphatase (ALPL; HGNC:436), bone alkaline phosphatase isoform; osteocalcin (BGLAP; HGNC:1048). Discussed as markers in SSCD biochemical evaluation (tikka2023investigationofserum pages 6-6). - Cochlin-tomoprotein (COCH fragment): Investigated as a specific inner-ear biomarker in perilymphatic disorders within third-window discourse (editorial context) (wackym2021editorialthirdwindow pages 3-4).
Cell types (CL) - Osteoclast (CL:0000098): Multinucleated bone-resorbing cells; implicated by broader temporal bone literature and bone marker context, though histology in one SCDS case did not show osteoclastic activity (teixido2012histopathologyofthe pages 1-2, tikka2023investigationofserum pages 6-6). - Osteoblast (CL:0000062) and bone lining cells: The otic capsule is characterized by bone quiescence with specialized lining cells; resurfacing (osteoneogenesis) observed in animal SSCD healing (wackym2023newmodelof pages 14-15). - Vestibular hair cells (e.g., CL:0000201) and afferent neurons: Activated by third-window pressure gradients/traveling waves, producing phase-locked and sustained responses (iversen2020biomechanicsofthird pages 6-7).
Anatomical locations (UBERON) - Superior semicircular canal (UBERON:0010740); otic capsule (UBERON:0001755); oval window (UBERON:0001752); round window (UBERON:0001753); utricle (UBERON:0001756). Lesion resides on vestibular side; thin or absent bone over SSC produces third-window mechanics (merchant2008conductivehearingloss pages 4-5, teixido2012histopathologyofthe pages 1-2, iversen2020biomechanicsofthird pages 6-7).
Chemical entities (CHEBI) - Calcium ion (CHEBI:29108); vitamin D (e.g., cholecalciferol, CHEBI:28940). Explored in SSCD case–control biochemistry (tikka2023investigationofserum pages 6-6).
Gene Ontology (GO) biological processes (disrupted or engaged) - Bone remodeling (GO:0046850) and regulation of osteoclast differentiation (GO:0045670): OPG/RANKL axis in otic capsule (tikka2023investigationofserum pages 6-6). - Mechanotransduction and sensory perception of sound (GO:0050957) and vestibular receptor cell stimulus detection (GO:0050911): Altered by third-window hydromechanics that impose abnormal pressure gradients/waves on hair cells (iversen2020biomechanicsofthird pages 6-7). - Endolymph and perilymph fluid transport dynamics (related to fluid shear and cupula deflection; aligns with GO terms such as cilium movement GO:0003341 in vestibular hair cell kinocilia context) (iversen2020biomechanicsofthird pages 6-7).
Cellular components (GO CC) - Otic capsule extracellular matrix (bone matrix) and perilymph/endolymph compartments; stereocilia bundle (GO:0032420) and cupula of ampulla (anatomical structure). Third-window mechanics produce transmembrane pressure differences across these compartments (iversen2020biomechanicsofthird pages 6-7, merchant2008conductivehearingloss pages 4-5).
Disease Progression (sequence of events) 1) Predisposition: Congenitally thin otic capsule bone over SSC and/or developmental anatomy predisposes to third-window formation; systemic mineral metabolism might modulate risk (teixido2012histopathologyofthe pages 1-2, tikka2023investigationofserum pages 6-6). 2) Trigger: Minor trauma, pressure events, or chronic pulsation at the middle cranial fossa can disrupt thin bone, creating a dehiscence with dura contacting the membranous duct (teixido2012histopathologyofthe pages 1-2). 3) Third-window hydromechanics: Dehiscence lowers vestibular-side impedance, shunting sound/pressure and generating pressure gradients and traveling waves in the vestibular labyrinth (merchant2008conductivehearingloss pages 4-5, iversen2020biomechanicsofthird pages 6-7). 4) Sensory consequences: Hair-bundle vibration and cupular deflection evoke phase-locked and sustained vestibular afferent activity, respectively; cochlear energy shunting yields low-frequency air–bone gaps with supranormal bone conduction (iversen2020biomechanicsofthird pages 6-7, merchant2008conductivehearingloss pages 4-5). 5) Clinical manifestation: Autophony, aural fullness, pulsatile tinnitus, sound/pressure-induced vertigo/oscillopsia, and conductive-pattern hearing loss. Diagnostics: low-threshold/high-amplitude VEMPs, CT-visible dehiscence, ECoG SP/AP changes (teixido2012histopathologyofthe pages 1-2, merchant2008conductivehearingloss pages 4-5, iversen2020biomechanicsofthird pages 6-7, wackym2021editorialthirdwindow pages 3-4). 6) Repair/healing: Surgical plugging/resurfacing often normalizes diagnostics and symptoms; in animal models, osteoneogenesis can resurface the defect and reverse electrophysiologic changes (merchant2008conductivehearingloss pages 4-5, wackym2023newmodelof pages 1-2, wackym2023newmodelof pages 14-15).
Phenotypic manifestations (HP) and links to mechanism - Tullio phenomenon (HP:0011510) and Hennebert sign (HP:0033533): Sound/pressure-induced vertigo/oscillopsia due to third-window-driven vestibular activation (iversen2020biomechanicsofthird pages 6-7, merchant2008conductivehearingloss pages 4-5). - Autophony (HP:0001601) and pulsatile tinnitus (HP:0000842): Aberrant hydromechanics and direct transmission pathways in third-window states (teixido2012histopathologyofthe pages 1-2, merchant2008conductivehearingloss pages 4-5). - Conductive hearing impairment (air–bone gap) (HP:0000405; low-frequency): Shunting of acoustic energy at scala vestibuli side reduces cochlear partition drive; improves with plugging (merchant2008conductivehearingloss pages 4-5). - Abnormal VEMP (HP:0033781; low thresholds, high amplitudes): Enhanced vestibular sensitivity due to third-window impedance shunting (iversen2020biomechanicsofthird pages 6-7, wackym2023newmodelof pages 1-2).
Key mechanistic evidence (with direct supporting quotes where available) - “A third window will introduce a low mechanical impedance,” generating pressure gradients/waves that activate vestibular afferents; plugging abolishes phase-locked responses (Aug 2020; Frontiers in Neurology) (iversen2020biomechanicsofthird pages 6-7). - “To produce a conductive hearing loss the third window must be on the scala vestibuli side” and plugging “resolves the air–bone gap” (Apr 2008; Otology & Neurotology) (merchant2008conductivehearingloss pages 4-5). - “No osteoclastic process was evident within the otic capsule” in histology of a clinical SCDS case (Jan 2012; Ann Otol Rhinol Laryngol) (teixido2012histopathologyofthe pages 1-2). - SSCD model “heals in situ by bony resurfacing of the SSCD without obliteration,” with ABR and cVEMP changes reversing toward baseline (Jan 2023; Frontiers in Neurology) (wackym2023newmodelof pages 14-15, wackym2023newmodelof pages 1-2).
Evidence items (primary literature; URLs and dates) - Wackym PA et al. New model of superior semicircular canal dehiscence with reversible diagnostic findings characteristic of patients with the disorder. Frontiers in Neurology. Jan 2023. https://doi.org/10.3389/fneur.2022.1035478 (wackym2023newmodelof pages 1-2, wackym2023newmodelof pages 14-15). - Iversen MM, Rabbitt RD. Biomechanics of Third Window Syndrome. Frontiers in Neurology. Aug 2020. https://doi.org/10.3389/fneur.2020.00891 (iversen2020biomechanicsofthird pages 6-7). - Merchant SN, Rosowski JJ. Conductive Hearing Loss Caused by Third-Window Lesions of the Inner Ear. Otology & Neurotology. Apr 2008. https://doi.org/10.1097/mao.0b013e318161ab24 (merchant2008conductivehearingloss pages 4-5). - Teixidó M et al. Histopathology of the Temporal Bone in a Case of Superior Canal Dehiscence Syndrome. Ann Otol Rhinol Laryngol. Jan 2012. https://doi.org/10.1177/000348941212100102 (teixido2012histopathologyofthe pages 1-2). - Tikka T et al. Investigation of serum calcium and vitamin D levels in superior semicircular canal dehiscence syndrome: A case-control study. Journal of Otology. Jan 2023. https://doi.org/10.1016/j.joto.2022.12.005 (tikka2023investigationofserum pages 6-6). - Wackym PA et al. Editorial: Third Window Syndrome. Frontiers in Neurology. Jun 2021. https://doi.org/10.3389/fneur.2021.704095 (wackym2021editorialthirdwindow pages 3-4).
Notes and limitations - Direct genetic causality for SCDS remains unestablished; molecular insights largely relate to bone remodeling biology (e.g., OPG/RANKL pathways) and unique quiescence of otic capsule bone. Histopathology can show thin bone and dura contact without active osteoclastic resorption, though other temporal bone studies document osteoclastic activity in general (teixido2012histopathologyofthe pages 1-2, tikka2023investigationofserum pages 6-6). - While most mechanistic claims are grounded in biomechanical and histologic evidence, targeted molecular pathways beyond OPG in the otic capsule require further study in human SCDS.
References
(merchant2008conductivehearingloss pages 4-5): Saumil N. Merchant and John J. Rosowski. Conductive hearing loss caused by third-window lesions of the inner ear. Otology & Neurotology, 29:282-289, Apr 2008. URL: https://doi.org/10.1097/mao.0b013e318161ab24, doi:10.1097/mao.0b013e318161ab24. This article has 431 citations and is from a peer-reviewed journal.
(iversen2020biomechanicsofthird pages 6-7): Marta M. Iversen and Richard D. Rabbitt. Biomechanics of third window syndrome. Frontiers in Neurology, Aug 2020. URL: https://doi.org/10.3389/fneur.2020.00891, doi:10.3389/fneur.2020.00891. This article has 58 citations and is from a peer-reviewed journal.
(teixido2012histopathologyofthe pages 1-2): Michael Teixido, Brian Kung, John J. Rosowski, and Saumil N. Merchant. Histopathology of the temporal bone in a case of superior canal dehiscence syndrome. Annals of Otology, Rhinology & Laryngology, 121:12-7, Jan 2012. URL: https://doi.org/10.1177/000348941212100102, doi:10.1177/000348941212100102. This article has 30 citations.
(tikka2023investigationofserum pages 6-6): Theofano Tikka, Mohd Afiq Mohd Slim, Trung Ton, Anna Sheldon, Louise J. Clark, and Georgios Kontorinis. Investigation of serum calcium and vitamin d levels in superior semicircular canal dehiscence syndrome: a case control study. Journal of Otology, 18:49-54, Jan 2023. URL: https://doi.org/10.1016/j.joto.2022.12.005, doi:10.1016/j.joto.2022.12.005. This article has 2 citations and is from a peer-reviewed journal.
(wackym2023newmodelof pages 1-2): P. Ashley Wackym, Carey D. Balaban, Olivia J. Van Osch, Brian T. Morris, Mark-Avery Tamakloe, Victoria L. Salvatore, Sudan Duwadi, Jennifer D. Gay, and Todd M. Mowery. New model of superior semicircular canal dehiscence with reversible diagnostic findings characteristic of patients with the disorder. Frontiers in Neurology, Jan 2023. URL: https://doi.org/10.3389/fneur.2022.1035478, doi:10.3389/fneur.2022.1035478. This article has 6 citations and is from a peer-reviewed journal.
(wackym2023newmodelof pages 14-15): P. Ashley Wackym, Carey D. Balaban, Olivia J. Van Osch, Brian T. Morris, Mark-Avery Tamakloe, Victoria L. Salvatore, Sudan Duwadi, Jennifer D. Gay, and Todd M. Mowery. New model of superior semicircular canal dehiscence with reversible diagnostic findings characteristic of patients with the disorder. Frontiers in Neurology, Jan 2023. URL: https://doi.org/10.3389/fneur.2022.1035478, doi:10.3389/fneur.2022.1035478. This article has 6 citations and is from a peer-reviewed journal.
(wackym2021editorialthirdwindow pages 3-4): P. Ashley Wackym, Yuri Agrawal, Tetsuo Ikezono, and Carey D. Balaban. Editorial: third window syndrome. Frontiers in Neurology, Jun 2021. URL: https://doi.org/10.3389/fneur.2021.704095, doi:10.3389/fneur.2021.704095. This article has 26 citations and is from a peer-reviewed journal.
name: Semicircular Canal Dehiscence Syndrome
creation_date: '2026-01-08T22:33:12Z'
updated_date: '2026-03-04T20:35:00Z'
category: Structural
disease_term:
preferred_term: semicircular canal dehiscence syndrome
term:
id: MONDO:0018484
label: semicircular canal dehiscence syndrome
parents:
- Inner Ear Disease
- Vestibular Disorder
synonyms:
- Superior Canal Dehiscence Syndrome
- SCDS
- Superior Semicircular Canal Dehiscence
- Third Window Syndrome
- Minor Syndrome
pathophysiology:
- name: Bony Dehiscence of Semicircular Canal
description: >-
An abnormal opening or thinning in the bone overlying the superior semicircular
canal
creates a pathological third mobile window in the inner ear, in addition to the
oval
and round windows. This dehiscence may result from congenitally thin otic capsule
bone predisposition with subsequent trauma trigger.
locations:
- preferred_term: superior semicircular canal
term:
id: UBERON:0001841
label: anterior semicircular canal
- preferred_term: otic capsule
term:
id: UBERON:0005411
label: bony otic capsule
evidence:
- reference: PMID:22312921
reference_title: "Histopathology of the temporal bone in a case of superior canal dehiscence syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Histopathologic examination of the right ear showed a 1.4 x 0.6-mm dehiscence
of bone covering the superior canal. Dura was in direct contact with the endosteum
and the membranous duct at the level of the dehiscence.
explanation: >-
Histopathological examination confirmed the anatomical basis of the dehiscence
with direct dura-to-membranous duct contact at the bony defect.
downstream:
- target: Third Window Effect
description: >-
The bony defect creates a pathological third mobile window in the inner ear labyrinth.
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Superior canal dehiscence causes vestibular and auditory symptoms and signs
as a consequence of the third mobile window in the inner ear created by
the dehiscence.
explanation: >-
Clinical series conclusion directly supports that the canal dehiscence creates
the third-window lesion.
- name: Third Window Effect
description: >-
The dehiscence acts as a third mobile window that shunts acoustic energy away
from
the cochlea and toward the vestibular system. A third window introduces a low
mechanical impedance, shunting part of the inner ear fluid pressure and fluid
volume flow at the site of the window.
biological_processes:
- preferred_term: vestibular receptor stimulus detection
term:
id: GO:0050973
label: detection of mechanical stimulus involved in equilibrioception
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
If sufficiently large, a third window will introduce a low mechanical impedance,
thus shunting part of the inner ear fluid pressure and fluid volume flow at
the
site of the window.
explanation: >-
This biomechanical review explains how the dehiscence creates abnormal fluid
dynamics by introducing a low-impedance pathway.
- reference: PMID:18223508
reference_title: "Conductive hearing loss caused by third-window lesions of the inner ear."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
A number of disparate disorders affecting the labyrinth can produce CHL by
acting as a pathologic third window in the inner ear. The common denominator
is that these conditions result in a mobile window on the scala vestibuli side
of the cochlear partition.
explanation: >-
This landmark paper establishes the third window mechanism as the cause of
the conductive hearing loss pattern seen in SCDS.
downstream:
- target: Abnormal Sound and Pressure Transmission
description: >-
The low-impedance third window allows sound and pressure energy to aberrantly
stimulate vestibular end-organs.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Symptoms include vestibular indications such as eye movements or dizziness
evoked by sound or middle ear/intracranial pressure changes
explanation: >-
Review synthesis links third-window mechanics to abnormal sound- and pressure-evoked
vestibular stimulation.
- target: Conductive Hearing Loss
description: >-
Acoustic energy is shunted away from the cochlea through the dehiscence,
worsening air conduction while enhancing bone conduction.
evidence:
- reference: PMID:18223508
reference_title: "Conductive hearing loss caused by third-window lesions of the inner ear."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The CHL results by the dual mechanism of worsening of air conduction thresholds
and improvement of bone conduction thresholds.
explanation: >-
Directly supports the third-window hearing mechanism with reduced air conduction
and enhanced bone conduction.
- target: Autophony
description: >-
Enhanced bone conduction through the third window amplifies perception of
body-generated sounds including voice, breathing, and heartbeat.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
and auditory indications such as autophony, hyperacusis for bone-conducted sounds,
conductive hearing loss, and tinnitus.
explanation: >-
Review describes autophony among characteristic third-window auditory manifestations.
- target: Hyperacusis
description: >-
Increased sensitivity to bone-conducted sounds due to the low-impedance
third window pathway.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
and auditory indications such as autophony, hyperacusis for bone-conducted sounds,
conductive hearing loss, and tinnitus.
explanation: >-
Same review supports hyperacusis as part of the third-window auditory phenotype cluster.
- target: Pulsatile Tinnitus
description: >-
Intracranial vascular pulsations are transmitted to the cochlea via the
third window.
evidence:
- reference: PMID:22312921
reference_title: "Histopathology of the temporal bone in a case of superior canal dehiscence syndrome."
supports: PARTIAL
evidence_source: HUMAN_CLINICAL
snippet: >-
The patient developed bilateral aural fullness, pulsatile tinnitus, and
difficulty tolerating loud noises after minor head trauma at 53 years of age.
explanation: >-
Case-level evidence supports pulsatile tinnitus in SCDS; specific fluid-mechanics
mediation is inferred.
- name: Abnormal Sound and Pressure Transmission
description: >-
Sounds and pressure changes that normally would not affect the vestibular system
can now stimulate the superior semicircular canal, leading to vestibular symptoms
triggered by loud sounds (Tullio phenomenon) or pressure changes (Hennebert sign).
Sound energy diverted toward the dehiscence generates pressure differences across
the membranous vestibular labyrinth that excite traveling waves.
cell_types:
- preferred_term: vestibular hair cell
term:
id: CL:0000609
label: vestibular hair cell
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Third window syndrome describes a set of vestibular and auditory symptoms that
arise when a pathological third mobile window is present in the bony labyrinth
of the inner ear.
explanation: >-
The biomechanics review explains how the third window allows sound and pressure
to inappropriately stimulate vestibular structures.
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
For the 60 patients with vestibular manifestations, symptoms induced by loud
sounds were noted in 54 patients and pressure-induced symptoms (coughing,
sneezing, straining) were present in 44.
explanation: >-
Clinical data from the original case series demonstrates the high frequency
of sound- and pressure-induced symptoms in SCDS patients.
downstream:
- target: Vertigo
description: >-
Sound and pressure inappropriately deflect the cupula of the superior
semicircular canal, triggering vestibular responses.
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
For the 60 patients with vestibular manifestations, symptoms induced by loud
sounds were noted in 54 patients and pressure-induced symptoms (coughing,
sneezing, straining) were present in 44.
explanation: >-
Large clinical series supports sound- and pressure-evoked vestibular episodes
consistent with vertigo triggers.
- target: Sound-Induced Nystagmus
description: >-
Vestibular stimulation by loud sounds drives the vestibulo-ocular reflex,
producing nystagmus (Tullio phenomenon).
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Sound-evoked vertigo or nystagmus are now termed "Tullio phenomenon," often
exhibited as a symptom of third window syndrome.
explanation: >-
Review directly supports sound-evoked nystagmus as a hallmark manifestation.
- target: Chronic Disequilibrium
description: >-
Persistent low-level vestibular stimulation from ambient sound and pressure
fluctuations causes ongoing imbalance.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Symptoms include vestibular indications such as eye movements or dizziness
evoked by sound or middle ear/intracranial pressure changes, chronic
disequilibrium, oscillopsia
explanation: >-
Review includes chronic disequilibrium in the vestibular symptom profile of SSCD.
- name: Otic Capsule Bone Biology
description: >-
The otic capsule exhibits unique bone physiology with greatly suppressed remodeling.
Histopathological examination shows absence of active bone resorption in SCDS
cases,
supporting developmental thin-bone predisposition rather than active resorption.
cell_types:
- preferred_term: osteoclast
term:
id: CL:0000092
label: osteoclast
- preferred_term: osteoblast
term:
id: CL:0000062
label: osteoblast
biological_processes:
- preferred_term: bone remodeling
term:
id: GO:0046849
label: bone remodeling
evidence:
- reference: PMID:22312921
reference_title: "Histopathology of the temporal bone in a case of superior canal dehiscence syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
No osteoclastic process was evident within the otic capsule bone surrounding
the dehiscence.
explanation: >-
Histopathological examination showed absence of active bone resorption,
supporting developmental thin-bone predisposition rather than active resorption.
downstream:
- target: Bony Dehiscence of Semicircular Canal
description: >-
Congenitally thin or underdeveloped otic capsule bone provides the structural
substrate for subsequent dehiscence formation.
evidence:
- reference: PMID:22312921
reference_title: "Histopathology of the temporal bone in a case of superior canal dehiscence syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The findings were consistent with the hypothesis put forth by Carey and colleagues
that SCD may arise from a failure of postnatal bone development, and that
minor trauma may disrupt thin bone or stable dura over the superior canal.
explanation: >-
Histopathology-based conclusion supports developmental thin-bone predisposition
contributing to dehiscence formation.
phenotypes:
- category: Vestibular
name: Vertigo
frequency: VERY_FREQUENT
description: >-
Episodic vertigo triggered by loud sounds or pressure changes such as coughing,
sneezing, or straining.
phenotype_term:
preferred_term: Vertigo
term:
id: HP:0002321
label: Vertigo
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
For the 60 patients with vestibular manifestations, symptoms induced by loud
sounds were noted in 54 patients and pressure-induced symptoms (coughing,
sneezing, straining) were present in 44.
explanation: >-
The original clinical series demonstrates that the vast majority of SCDS
patients experience sound- or pressure-induced vestibular symptoms.
sequelae:
- target: Chronic Disequilibrium
description: >-
Recurrent vertigo episodes contribute to persistent sensation of imbalance.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: PARTIAL
evidence_source: OTHER
snippet: >-
Symptoms include vestibular indications such as eye movements or dizziness
evoked by sound or middle ear/intracranial pressure changes, chronic
disequilibrium, oscillopsia
explanation: >-
Source supports coexistence of vertigo/dizziness and chronic disequilibrium;
directional progression is plausible but not directly tested.
- category: Vestibular
name: Sound-Induced Nystagmus
frequency: VERY_FREQUENT
description: >-
Vestibular symptoms including eye movements (nystagmus) induced by loud sounds,
also known as Tullio phenomenon.
phenotype_term:
preferred_term: Nystagmus
term:
id: HP:0000639
label: Nystagmus
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Sound-evoked vertigo or nystagmus are now termed "Tullio phenomenon," often
exhibited as a symptom of third window syndrome.
explanation: >-
The biomechanics review confirms that sound-evoked nystagmus (Tullio phenomenon)
is a characteristic feature of third window syndrome.
sequelae:
- target: Oscillopsia
description: >-
Involuntary eye movements driven by vestibular stimulation cause perception
of visual oscillation.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: PARTIAL
evidence_source: OTHER
snippet: >-
Symptoms include vestibular indications such as eye movements or dizziness
evoked by sound or middle ear/intracranial pressure changes, chronic
disequilibrium, oscillopsia
explanation: >-
Review supports linkage between vestibular eye-movement symptoms and oscillopsia,
though edge-level causality is inferential.
- category: Vestibular
name: Oscillopsia
frequency: FREQUENT
description: >-
Visual disturbance in which objects appear to oscillate, particularly during
movement or exposure to triggering stimuli.
phenotype_term:
preferred_term: Oscillopsia
term:
id: HP:0034773
label: Oscillopsia
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Symptoms include vestibular indications such as eye movements or dizziness
evoked by sound or middle ear/intracranial pressure changes, chronic
disequilibrium, oscillopsia
explanation: >-
Oscillopsia is listed as one of the vestibular symptoms in SCDS.
- category: Auditory
name: Autophony
frequency: VERY_FREQUENT
description: >-
Abnormally loud perception of one's own voice, breathing, heartbeat, or eye
movements due to enhanced bone conduction.
phenotype_term:
preferred_term: Autophony
term:
id: HP:6000032
label: Autophony
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
and auditory indications such as autophony, hyperacusis for bone-conducted sounds,
conductive hearing loss, and tinnitus.
explanation: >-
Autophony is described as a characteristic auditory symptom of SCDS.
- category: Auditory
name: Pulsatile Tinnitus
frequency: FREQUENT
description: >-
Perception of rhythmic sounds synchronous with the heartbeat.
phenotype_term:
preferred_term: Pulsatile tinnitus
term:
id: HP:0008629
label: Pulsatile tinnitus
evidence:
- reference: PMID:22312921
reference_title: "Histopathology of the temporal bone in a case of superior canal dehiscence syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The patient developed bilateral aural fullness, pulsatile tinnitus, and
difficulty tolerating loud noises after minor head trauma at 53 years of age.
explanation: >-
Pulsatile tinnitus is documented as a presenting symptom in this SCDS case.
- category: Auditory
name: Conductive Hearing Loss
frequency: FREQUENT
description: >-
Low-frequency conductive hearing loss due to shunting of acoustic energy through
the dehiscence rather than to the cochlea. Characterized by air-bone gap with
sometimes supranormal bone conduction thresholds.
phenotype_term:
preferred_term: Conductive hearing impairment
term:
id: HP:0000405
label: Conductive hearing impairment
evidence:
- reference: PMID:18223508
reference_title: "Conductive hearing loss caused by third-window lesions of the inner ear."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
The CHL results by the dual mechanism of worsening of air conduction thresholds
and improvement of bone conduction thresholds.
explanation: >-
This landmark paper explains the mechanism of pseudoconductive hearing loss
in third window lesions.
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
An air-bone on audiometry in these patients with vestibular manifestations
measured (mean +/- SD) 19 +/- 14 dB at 250 Hz; 15 +/- 11 dB at 500 Hz;
11 +/- 9 dB at 1,000 Hz; and 4 +/- 6 dB at 2,000 Hz.
explanation: >-
Clinical data demonstrates the characteristic low-frequency air-bone gap
pattern in SCDS patients.
- category: Vestibular
name: Chronic Disequilibrium
frequency: FREQUENT
description: >-
Persistent sensation of imbalance or unsteadiness.
phenotype_term:
preferred_term: Gait imbalance
term:
id: HP:0002141
label: Gait imbalance
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Symptoms include vestibular indications such as eye movements or dizziness
evoked by sound or middle ear/intracranial pressure changes, chronic
disequilibrium, oscillopsia
explanation: >-
Chronic disequilibrium is listed as one of the vestibular symptoms in SCDS.
- category: Auditory
name: Hyperacusis
frequency: OCCASIONAL
description: >-
Increased sensitivity to bone-conducted sounds.
phenotype_term:
preferred_term: Hyperacusis
term:
id: HP:0010780
label: Hyperacusis
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
and auditory indications such as autophony, hyperacusis for bone-conducted sounds,
conductive hearing loss, and tinnitus.
explanation: >-
Hyperacusis is listed as an auditory symptom of SCDS.
biochemical:
genetic:
environmental:
- name: Minor Head Trauma
presence: Triggering
description: >-
Minor head trauma may precipitate symptom onset in anatomically predisposed
individuals with thin superior canal bone.
effect: Can trigger clinical decompensation of previously compensated dehiscence.
evidence:
- reference: PMID:22312921
reference_title: "Histopathology of the temporal bone in a case of superior canal dehiscence syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The patient developed bilateral aural fullness, pulsatile tinnitus, and
difficulty tolerating loud noises after minor head trauma at 53 years of age.
explanation: >-
Case-level evidence supports minor head trauma as a precipitating trigger
for symptomatic SCDS.
- reference: PMID:22312921
reference_title: "Histopathology of the temporal bone in a case of superior canal dehiscence syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The findings were consistent with the hypothesis put forth by Carey and colleagues
that SCD may arise from a failure of postnatal bone development, and that
minor trauma may disrupt thin bone or stable dura over the superior canal.
explanation: >-
Histopathology paper explicitly supports developmental predisposition with
trauma-triggered symptom emergence.
- name: Loud Sound and Pressure Changes
presence: Triggering
description: >-
Loud sounds and pressure maneuvers (coughing, sneezing, straining, Valsalva)
frequently provoke vestibular symptoms.
effect: Triggers vertigo, nystagmus, and dizziness episodes.
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
For the 60 patients with vestibular manifestations, symptoms induced by loud
sounds were noted in 54 patients and pressure-induced symptoms (coughing,
sneezing, straining) were present in 44.
explanation: >-
Large clinical cohort demonstrates that sound and pressure triggers are common
provoking factors in SCDS.
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Patients with mild symptoms can reduce exposure to loud sounds and avoid
physical straining, and those with pressure sensitivity can benefit from
a tympanostomy tube
explanation: >-
Review guidance reinforces clinical relevance of these trigger exposures in
day-to-day symptom control.
treatments:
- name: Observation and Symptom Management
description: >-
For mild cases, conservative management including avoidance of triggering stimuli
and vestibular rehabilitation may be sufficient. Patients with pressure sensitivity
can benefit from a tympanostomy tube.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Patients with mild symptoms can reduce exposure to loud sounds and avoid
physical straining, and those with pressure sensitivity can benefit from
a tympanostomy tube
explanation: >-
Conservative management options are described for patients with mild symptoms.
- name: Surgical Canal Plugging
description: >-
Surgical occlusion of the dehiscent superior semicircular canal via middle
cranial fossa or transmastoid approach to eliminate the third window effect.
Canal plugging achieves long-term control more often than resurfacing.
treatment_term:
preferred_term: surgical procedure
term:
id: MAXO:0000004
label: surgical procedure
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Canal plugging was performed in 9 and resurfacing of the canal without
plugging of the lumen in 11 patients. Complete resolution of vestibular
symptoms and signs was achieved in 8 of the 9 patients after canal plugging.
explanation: >-
Clinical data demonstrates high success rate of canal plugging surgery.
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Canal plugging achieves long-term control more often than resurfacing and
is usually the procedure of choice
explanation: >-
Canal plugging is established as the preferred surgical treatment.
- name: Surgical Resurfacing
description: >-
Surgical repair by placing bone graft or other material over the dehiscence
to restore normal inner ear mechanics without occluding the canal lumen.
treatment_term:
preferred_term: surgical procedure
term:
id: MAXO:0000004
label: surgical procedure
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Complete resolution of vestibular symptoms and signs was achieved in 8 of
the 9 patients after canal plugging and in 7 of the 11 patients after
resurfacing.
explanation: >-
Resurfacing can achieve symptom resolution, though less reliably than plugging.
- reference: PMID:36742050
reference_title: "New model of superior semicircular canal dehiscence with reversible diagnostic findings characteristic of patients with the disorder."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
The changes observed also reverse and return to baseline as the SSCD heals
by bone resurfacing (with the lumen intact).
explanation: >-
Animal model demonstrates that bony resurfacing can restore normal function
while preserving canal lumen patency.
diagnosis:
- name: High-Resolution CT Temporal Bone
description: >-
Thin-slice CT imaging of the temporal bone in multiple planes to visualize
the bony defect over the superior semicircular canal. While imaging is
important, false positives occur, motivating the use of physiological
indicators prior to CT imaging.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
High-resolution computed-tomography images of the temporal bone revealed
dehiscence of the bone above the superior semicircular canal, and imaging
was considered the gold standard for diagnosis for a number of years.
explanation: >-
CT imaging is essential for visualizing the dehiscence.
- name: Vestibular Evoked Myogenic Potentials (VEMP)
description: >-
Cervical and ocular VEMP testing shows reduced thresholds and increased
amplitudes characteristic of third window lesions. Thresholds normalize
after surgical repair.
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The threshold for eliciting vestibular-evoked myogenic potentials from
affected ears was (mean +/- SD) 81 +/- 9 dB normal hearing level. The
threshold for unaffected ears was 99 +/- 7 dB, and the threshold for
control ears was 98 +/- 4 dB.
explanation: >-
Clinical data demonstrates significantly reduced VEMP thresholds in
affected ears compared to unaffected and control ears.
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Vestibular Evoked Myogenic Potentials (VEMPs) provide a strong diagnostic
indicator of SSCD.
explanation: >-
VEMPs are established as a strong diagnostic indicator for SCDS.
- name: Audiometry
description: >-
May reveal characteristic low-frequency air-bone gap with normal bone
conduction or supranormal bone conduction thresholds, without middle ear
pathology. The air-bone gap is largest at low frequencies and diminishes
above 2000 Hz.
evidence:
- reference: PMID:18223508
reference_title: "Conductive hearing loss caused by third-window lesions of the inner ear."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Clues to suspect such a lesion include a low-frequency air-bone gap with
supranormal thresholds for bone conduction, and presence of acoustic
reflexes, vestibular evoked myogenic responses, or otoacoustic emission
responses despite the CHL.
explanation: >-
The audiometric pattern of low-frequency air-bone gap with supranormal
bone conduction is characteristic of third window lesions.
differential_diagnoses:
- name: Meniere Disease
disease_term:
preferred_term: Meniere disease
term:
id: MONDO:0007972
label: Meniere disease
description: >-
Inner-ear disorder with overlapping episodic vertigo, tinnitus, and aural
symptoms that can mimic SCDS.
distinguishing_features:
- SCDS more often has sound- and pressure-evoked symptoms (Tullio/Hennebert phenomena).
- Physiologic third-window findings (low-threshold VEMP, low-frequency air-bone gap with intact middle ear) favor SCDS.
- CT evidence of superior canal dehiscence supports SCDS rather than Meniere disease.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Since these studies, various causes of the Tullio phenomenon and Hennebert's
sign have been reported, such as perilymphatic fistula (9, 10), Ménière's
disease (11), and cholesteatoma (12).
explanation: >-
Review explicitly identifies Ménière's disease as a competing cause of similar
vestibular signs.
- name: Cholesteatoma
disease_term:
preferred_term: cholesteatoma
term:
id: MONDO:0006530
label: cholesteatoma
description: >-
Middle-ear disease that can produce pressure/sound-related vestibular findings
and auditory complaints overlapping with SCDS.
distinguishing_features:
- Structural middle-ear pathology on otologic exam/imaging favors cholesteatoma.
- Third-window physiology and superior canal bony defect support SCDS.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Since these studies, various causes of the Tullio phenomenon and Hennebert's
sign have been reported, such as perilymphatic fistula (9, 10), Ménière's
disease (11), and cholesteatoma (12).
explanation: >-
Same review explicitly includes cholesteatoma among key differential etiologies
of similar vestibular signs.
- name: Otosclerosis
disease_term:
preferred_term: otosclerosis
term:
id: MONDO:0005349
label: otosclerosis
description: >-
Common differential diagnosis for conductive hearing loss with an intact
tympanic membrane and may be mistaken for third-window hearing findings.
distinguishing_features:
- SCDS may show supranormal bone conduction and abnormal VEMP responses despite air-bone gap.
- Presence of vestibular sound/pressure triggers and CT-proven dehiscence supports SCDS.
evidence:
- reference: PMID:18223508
reference_title: "Conductive hearing loss caused by third-window lesions of the inner ear."
supports: PARTIAL
evidence_source: OTHER
snippet: >-
Third-window lesions should be considered in the differential diagnosis of CHL
in patients with an intact tympanic membrane and an aerated, otherwise healthy,
middle ear.
explanation: >-
Review highlights the need to distinguish third-window CHL (including SCDS)
from classic middle-ear conductive hearing disorders such as otosclerosis.
- name: Benign Paroxysmal Positional Vertigo
disease_term:
preferred_term: benign paroxysmal positional vertigo
term:
id: MONDO:8000018
label: benign paroxysmal positional vertigo
description: >-
Positional vertigo syndrome that overlaps symptomatically with vestibular
complaints in SCDS and may coexist in postoperative contexts.
distinguishing_features:
- BPPV is position-triggered without defining third-window auditory features.
- SCDS is characterized by sound/pressure-triggered vestibular symptoms plus third-window audiovestibular test abnormalities.
evidence:
- reference: PMID:32982922
reference_title: "Biomechanics of Third Window Syndrome."
supports: PARTIAL
evidence_source: OTHER
snippet: >-
New-onset benign paroxysmal positional vertigo has been reported in up to 25%
of postoperative patients likely due to otoconia or plugging material that
becomes mobilized in the endolymph (101).
explanation: >-
Review documents clinically relevant BPPV overlap/co-occurrence in SCDS care,
supporting its inclusion in differential consideration.
datasets:
- accession: PMID:16222184
title: Clinical manifestations of superior semicircular canal dehiscence
description: >-
Clinical cohort dataset from 65 SCDS patients including symptom triggers,
audiometric air-bone gaps, VEMP thresholds, and postsurgical outcomes for
canal plugging versus resurfacing.
organism:
preferred_term: Homo sapiens
term:
id: NCBITaxon:9606
label: Homo sapiens
sample_types:
- preferred_term: superior semicircular canal
term:
id: UBERON:0001841
label: anterior semicircular canal
sample_count: 65
conditions:
- vestibular manifestations
- exclusively auditory manifestations
notes: Clinical cohort summary dataset derived from published audiovestibular phenotyping; not a GA4GH Phenopacket resource.
publication: PMID:16222184
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
There were 65 patients who qualified for inclusion in this study on the basis
of these criteria.
explanation: >-
Defines the cohort size and supports this publication as a reusable clinical
phenotype dataset for SCDS.
findings:
- statement: >-
Most patients had sound- and pressure-triggered vestibular symptoms with
objective low-frequency air-bone gaps and reduced VEMP thresholds.
evidence:
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
For the 60 patients with vestibular manifestations, symptoms induced by loud
sounds were noted in 54 patients and pressure-induced symptoms (coughing,
sneezing, straining) were present in 44.
explanation: >-
Documents high prevalence of sound/pressure-triggered vestibular symptoms
in the cohort.
- reference: PMID:16222184
reference_title: "Clinical manifestations of superior semicircular canal dehiscence."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The threshold for eliciting vestibular-evoked myogenic potentials from affected
ears was (mean +/- SD) 81 +/- 9 dB normal hearing level.
explanation: >-
Provides objective physiological measurements characteristic of SCDS.
- accession: PMID:36742050
title: New model of superior semicircular canal dehiscence with reversible diagnostic findings characteristic of patients with the disorder
description: >-
Experimental gerbil SSCD dataset with longitudinal ABR and c+VEMP measurements
following superior semicircular canal fenestration, including recovery dynamics
during spontaneous bone resurfacing.
organism:
preferred_term: Meriones unguiculatus
term:
id: NCBITaxon:10047
label: Meriones unguiculatus
sample_types:
- preferred_term: superior semicircular canal
term:
id: UBERON:0001841
label: anterior semicircular canal
sample_count: 36
conditions:
- small 1 mm superior semicircular canal dehiscence
- large 2 mm superior semicircular canal dehiscence
- post-fenestration recovery with bone resurfacing
notes: Experimental physiology dataset (ABR/c+VEMP and micro-CT) extracted from publication; not a GA4GH Phenopacket resource.
publication: PMID:36742050
evidence:
- reference: PMID:36742050
reference_title: "New model of superior semicircular canal dehiscence with reversible diagnostic findings characteristic of patients with the disorder."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Adult Mongolian gerbils (n = 36) received surgical fenestration of the superior
semicircular canal of the left inner ear.
explanation: >-
Defines the model-organism cohort and intervention used to generate the dataset.
findings:
- statement: >-
Experimental SSCD caused low-frequency hearing threshold worsening and enhanced
cVEMP responses that normalized as the bony defect resurfaced.
evidence:
- reference: PMID:36742050
reference_title: "New model of superior semicircular canal dehiscence with reversible diagnostic findings characteristic of patients with the disorder."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
The SSCD created a significant worsening of hearing thresholds of the left ear;
especially in the lower frequency domain (1-4 kHz).
explanation: >-
Demonstrates pseudoconductive hearing phenotype in the model.
- reference: PMID:36742050
reference_title: "New model of superior semicircular canal dehiscence with reversible diagnostic findings characteristic of patients with the disorder."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
As the bone regrew, the c+VEMP and ABR responses returned toward preoperative
values.
explanation: >-
Supports reversibility of physiological abnormalities with spontaneous resurfacing.
notes: >-
Superior semicircular canal dehiscence syndrome was first described by Lloyd
Minor and colleagues in 1998. The condition is also known as Minor syndrome.
A cadaveric survey of 1,000 temporal bones found 0.5% had complete dehiscence
and another 1.4% had significant thinning of bone overlying the superior canal,
though clinical presentation of symptoms is less common than anatomic prevalence
suggests.
references:
- reference: DOI:10.1016/j.joto.2022.12.005
title: 'Investigation of serum calcium and vitamin D levels in superior semicircular
canal dehiscence syndrome: A case control study'
findings: []
- reference: DOI:10.1097/01.mao.0000244370.47320.9a
title: Measurements of Human Middle- and Inner-Ear Mechanics With Dehiscence
of the Superior Semicircular Canal
findings: []
- reference: DOI:10.1097/01.mlg.0000150702.28451.35
title: Osteoprotegerin in the Inner Ear May Inhibit Bone Remodeling in the
Otic Capsule
findings: []
- reference: DOI:10.1097/mao.0b013e318161ab24
title: Conductive Hearing Loss Caused by Third-Window Lesions of the Inner Ear
findings: []
- reference: DOI:10.1177/000348941212100102
title: Histopathology of the Temporal Bone in a Case of Superior Canal
Dehiscence Syndrome
findings: []
- reference: DOI:10.3389/fneur.2020.00891
title: Biomechanics of Third Window Syndrome
findings: []
- reference: DOI:10.3389/fneur.2021.704095
title: 'Editorial: Third Window Syndrome'
findings: []
- reference: DOI:10.3389/fneur.2022.1035478
title: New model of superior semicircular canal dehiscence with reversible
diagnostic findings characteristic of patients with the disorder
findings: []