Superior Semicircular Canal Dehiscence (SSCD)
The diagnosis is C. Superior semicircular canal dehiscence (SSCD), based on the classic triad of autophony, hearing loss, and preserved stapedial reflex with a normal tympanic membrane. 1
Key Diagnostic Features That Distinguish SSCD
Clinical Presentation
- Autophony is the hallmark symptom, occurring in 94% of SSCD cases, often described as hearing one's own voice abnormally loud or a "blocked ear" sensation 1
- Tinnitus is present in approximately 27% of SSCD patients 2
- The preserved stapedial reflex is critical—acoustic reflex remains intact in 89% of SSCD cases despite the conductive hearing loss pattern 1
- Normal tympanic membrane on otoscopic examination rules out middle ear pathology 3
Audiometric Pattern
- SSCD characteristically produces a pseudoconductive hearing loss (air-bone gap) in 86% of cases 1
- Supranormal bone conduction thresholds (better than 0 dB HL) at 250 and/or 500 Hz occur in 60% of dehiscence ears, which is pathognomonic for third window lesions 1
- Hearing loss patterns vary: mixed hearing loss (36%), conductive hearing loss (27%), profound sensorineural hearing loss (18%), or even normal hearing (18%) 2
Why Not the Other Diagnoses
Otosclerosis (Option A) - Excluded
- Stapedial reflex would be absent or elevated in otosclerosis due to stapes fixation 4
- Autophony is not a typical feature of otosclerosis 4
- The preserved stapedial reflex in this patient definitively rules out otosclerosis 1
Patulous Eustachian Tube (Option B) - Excluded
- While patulous eustachian tube can cause autophony, patients typically report autophony of nasal breathing, which is absent in SSCD 1
- Patulous eustachian tube symptoms worsen with standing and improve when supine or with Valsalva 1
- Stapedial reflexes would be normal in patulous eustachian tube, but the hearing loss pattern and tinnitus do not fit 5
- SSCD mimics patulous eustachian tube but can be distinguished by the absence of autophony with nasal breathing 1
Confirmatory Testing Algorithm
First-Line Diagnostic Tests
- High-resolution CT scan with Pöschl and Stenvers reconstructions to visualize the bony dehiscence over the superior semicircular canal 1
- Vestibular evoked myogenic potential (VEMP) testing shows abnormally low thresholds with 91.4% sensitivity and 95.8% specificity for SSCD 1
- Comprehensive audiometry demonstrating the characteristic low-frequency air-bone gap with supranormal bone conduction 1
Physical Examination Findings
- Hennebert sign (nystagmus with pneumatic otoscopy) present in 73% of SSCD cases 2
- Tullio phenomenon (vertigo induced by loud sounds) occurs in 64% of cases 2
- Vertical-torsional nystagmus away from the affected ear when loud noise is applied or with Valsalva maneuver 6
Critical Clinical Pearls
- No correlation exists between dehiscence size and symptom severity or degree of hearing loss 2
- SSCD is a "great otologic mimicker" that can present with diverse manifestations 1
- The combination of conductive hearing loss with better than 0 dB bone conduction threshold, normal tympanometry, and intact acoustic reflexes is virtually diagnostic 1
- VEMP testing may be more sensitive than CT imaging—one case series found a false-positive CT but VEMP correctly identified posterior semicircular canal dehiscence at surgery 1