Superior Semicircular Canal Dehiscence (SSCD)
The most likely 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.
Key Diagnostic Features That Point to SSCD
The clinical presentation strongly suggests SSCD rather than the other options:
Autophony with preserved stapedial reflex is pathognomonic for SSCD 1. This combination essentially rules out otosclerosis, where the stapedial reflex is typically absent due to stapes fixation.
Normal tympanic membrane excludes patulous eustachian tube as the primary diagnosis 1. While patulous eustachian tube can cause autophony, patients typically report autophony of nasal breathing and relief with supine positioning, whereas SSCD patients primarily experience autophony of their own voice 1.
The preserved (intact) stapedial reflex is found in 89% of SSCD cases 1, which is a critical distinguishing feature from otosclerosis where the reflex is absent.
Why Not Otosclerosis?
Otosclerosis would present with:
- Absent stapedial reflex due to stapes fixation, which directly contradicts this patient's preserved reflex 1
- Typically bilateral presentation (though can be unilateral initially)
- Progressive conductive hearing loss without autophony as a primary complaint
Why Not Patulous Eustachian Tube?
While patulous eustachian tube can mimic SSCD with autophony and "blocked ear" sensation:
- Patients with patulous eustachian tube report autophony of nasal breathing, not just voice 1
- Relief occurs with Valsalva or supine position in 50% of patulous eustachian tube cases 1, but this also occurs in SSCD, making it non-specific
- The preserved stapedial reflex and hearing loss pattern favor SSCD
Essential Diagnostic Workup Required
To confirm SSCD diagnosis:
High-resolution CT temporal bone with Pöschl and Stenvers reconstructions is the imaging gold standard to visualize the bony dehiscence 1
Audiometry will likely show pseudoconductive hearing loss (air-bone gap with supranormal bone conduction thresholds, particularly better than 0 dB HL at 250-500 Hz in 60% of cases) 1
Vestibular evoked myogenic potential (VEMP) testing demonstrates 91.4% sensitivity and 95.8% specificity for SSCD, with abnormally low thresholds and increased amplitude 1, 2
Tympanometry will be normal, confirming middle ear function is intact 1
Clinical Pearls and Pitfalls
Common presenting symptoms of SSCD include 1:
- Autophony of voice and "blocked ear" sensation (94% of cases)
- Pulsatile tinnitus 3, 4
- Pressure or noise-induced vertigo (Tullio phenomenon in 64% of cases) 2
- Chronic disequilibrium (73% of cases) 2
Critical diagnostic error to avoid: Do not assume conductive hearing loss with a normal tympanic membrane is automatically otosclerosis without checking the stapedial reflex 1. The intact reflex essentially excludes otosclerosis and should prompt evaluation for third-window lesions like SSCD.
No correlation exists between dehiscence size and symptom severity 2, so even small dehiscences can cause significant symptoms.
If CT is negative but clinical suspicion remains high with abnormal VEMP, consider posterior semicircular canal dehiscence or cochlear-facial dehiscence 1, 4, as VEMP may be more sensitive than CT in some cases.