Superior Semicircular Canal Dehiscence (SSCD)
The diagnosis is C. Superior semicircular canal dehiscence (SSCD). The preserved stapedial reflex is the key distinguishing feature that rules out otosclerosis and points toward SSCD, while the combination of hearing loss, tinnitus, and autophony with a normal tympanic membrane makes this diagnosis far more likely than patulous eustachian tube.1
Why SSCD Is the Correct Diagnosis
The preserved (intact) stapedial reflex is pathognomonic for SSCD in this clinical context. The "third-window" effect created by the dehiscence does not interfere with middle ear mechanics or stapedius muscle function, allowing the reflex to remain intact despite the conductive hearing loss.1 In fact, acoustic reflexes are present in 89% of SSCD cases.2
Classic SSCD Presentation in This Patient
- Autophony is the hallmark symptom, reported in 94% of SSCD patients, and specifically involves hearing one's own voice abnormally loud (not breathing sounds, which helps differentiate from patulous eustachian tube).2, 3
- Hearing loss in SSCD typically manifests as a pseudoconductive loss with low-frequency predominance; 60% of affected ears demonstrate bone conduction thresholds better than 0 dB at 250-500 Hz.2
- Tinnitus commonly accompanies SSCD.2
- Normal tympanic membrane on examination is expected, as SSCD is an inner ear pathology.2
Why NOT Otosclerosis (Option A)
Otosclerosis is definitively excluded by the preserved stapedial reflex. Stapes fixation in otosclerosis characteristically produces an absent or diminished stapedial reflex because the fixed stapes cannot transmit the reflex arc properly.1 This is one of the most reliable differentiating features between these two conditions.4
Additionally, otosclerosis does not typically cause autophony, which is a prominent feature in this patient.5
Why NOT Patulous Eustachian Tube (Option B)
While patulous eustachian tube can cause autophony and a sensation of ear fullness, several features argue strongly against this diagnosis:
- Autophony of breathing sounds is the defining feature of patulous ET (hearing one's own nasal breathing), not just voice autophony.3, 6 This patient's presentation emphasizes voice autophony, which is characteristic of SSCD.2, 3
- Tympanic membrane movement with respiration is the classic objective finding in patulous ET, which would be visible on examination.6 This patient has a normal tympanic membrane examination.
- Relief with Valsalva or lying supine occurs in 50% of patulous ET cases but is also seen in SSCD, making it non-specific.2
- The preserved stapedial reflex and hearing loss pattern are not explained by patulous ET, which typically does not cause significant hearing loss.3
Critical clinical pearl: Autophony of voice (but not breathing) is experienced by 94% of SSCD patients and can easily be mistaken for patulous ET.3 The key differentiator is that SSCD patients do not report autophony of nasal breathing.2
Diagnostic Confirmation Strategy
Order high-resolution CT of the temporal bone with Pöschl and Stenvers reconstructions to directly visualize the superior semicircular canal dehiscence.7, 1, 2 This is the gold standard imaging test.
Obtain vestibular evoked myogenic potential (VEMP) testing, which shows abnormally low (reduced) thresholds in SSCD with 91.4% sensitivity and 95.8% specificity.1, 2 VEMP may actually be more sensitive than CT for detecting canal dehiscence.2
Perform complete audiometry looking for the characteristic pseudoconductive loss with bone conduction thresholds better than 0 dB at low frequencies (250-500 Hz), which occurs in 60% of SSCD cases.2
Common Diagnostic Pitfall
Do not confuse SSCD with patulous eustachian tube based solely on autophony. Always ask specifically about autophony of breathing sounds versus voice only, and check for tympanic membrane movement with respiration.3, 6 The presence of hearing loss, tinnitus, and preserved stapedial reflexes should immediately raise suspicion for SSCD rather than patulous ET.2, 3