Superior Semicircular Canal Dehiscence (SSCD)
The diagnosis is C: Superior semicircular canal dehiscence (SSCD). The combination of autophony, tinnitus, hearing loss, and a preserved stapedial reflex with a normal tympanic membrane is pathognomonic for SSCD, not otosclerosis or patulous Eustachian tube 1.
Key Diagnostic Features That Distinguish SSCD
The preserved stapedial reflex is the critical distinguishing feature. In SSCD, the "third-window" effect creates an abnormal pathway for sound transmission but does not interfere with middle ear mechanics or stapedius muscle function, leaving the stapedial reflex intact 1. This single finding effectively rules out otosclerosis, which characteristically produces an absent or diminished stapedial reflex due to stapes fixation 1.
Why Not Otosclerosis (Option A)?
- Otosclerosis causes absent or diminished stapedial reflexes due to ossicular fixation, which directly contradicts this patient's preserved reflex 1
- The normal tympanic membrane also argues against otosclerosis, though this is less specific 1
Why Not Patulous Eustachian Tube (Option B)?
- Patulous Eustachian tube does not typically cause hearing loss or tinnitus as primary features 2, 3, 4
- The hallmark of patulous ET is breath autophony (hearing one's own breathing sounds), not just voice autophony 2, 3, 5
- Patients with patulous ET characteristically report relief with head-dependent positioning (lying down) and worsening with exercise or weight loss 5
- The stapedial reflex is typically normal in patulous ET, but this finding alone does not distinguish it from SSCD 2
- Critical pitfall: Autophony from SSCD can be easily mistaken for patulous ET—94% of SSCD patients experience voice autophony that mimics patulous ET 3
Confirmatory Diagnostic Workup
Order high-resolution CT of the temporal bone to directly visualize the bony dehiscence of the superior semicircular canal 1, 6. This is the definitive imaging study for SSCD and should be performed in all suspected cases 6, 1.
Obtain vestibular evoked myogenic potential (VEMP) testing to provide supportive objective evidence—SSCD characteristically shows abnormally low (reduced) thresholds, not elevated thresholds 1. This electrophysiologic finding strengthens the diagnosis when combined with imaging.
Clinical Context and Mechanism
- SSCD creates a "third window" in the inner ear that allows abnormal transmission of vascular sounds (causing pulsatile tinnitus) and the patient's own voice (causing autophony) 6, 1
- The condition can present with both pulsatile and non-pulsatile tinnitus, along with pressure-induced or sound-induced symptoms that vary with Valsalva or position changes 6, 7
- Unilateral presentation is typical, as seen in this patient with left-sided symptoms 6, 7
Common Diagnostic Pitfall
The most dangerous error is confusing SSCD autophony with patulous Eustachian tube. Both conditions cause voice autophony, but SSCD also produces hearing loss and tinnitus, while patulous ET primarily causes breath autophony without significant hearing impairment 3, 5. The preserved stapedial reflex distinguishes SSCD from otosclerosis but does not differentiate it from patulous ET—you must rely on the full symptom constellation (hearing loss + tinnitus + autophony) and confirmatory imaging 1, 3.