What is the likely diagnosis for a patient with left hearing loss (HL), tinnitus, autophony, and a preserved stapedial reflex, with a normal tympanic membrane on examination?

Diagnosis: Superior Semicircular Canal Dehiscence (SSCD)

The most likely diagnosis is superior semicircular canal dehiscence (SSCD), given the classic triad of autophony, hearing loss, and tinnitus with a preserved stapedial reflex and normal tympanic membrane.

Clinical Reasoning

Key Diagnostic Features Present

The combination of symptoms points definitively toward SSCD:

• Autophony is the pathognomonic symptom that distinguishes SSCD from other causes of conductive hearing loss 1
• Preserved stapedial reflex effectively rules out otosclerosis, which typically causes stapedial reflex absence due to stapes fixation 2, 3
• Normal tympanic membrane excludes middle ear pathology like effusion or perforation 4
• Tinnitus is commonly associated with third-window lesions like SSCD 1, 5

Why Not Otosclerosis (Option A)

Otosclerosis would present with:

• Absent or elevated stapedial reflex thresholds due to stapes fixation 2, 3
• Progressive hearing loss typically starting in the second to fifth decade 2
• Tinnitus in 60-90% of cases, but autophony is not a characteristic feature 6
• The preserved stapedial reflex in this patient essentially excludes otosclerosis 3

Why Not Patulous Eustachian Tube (Option B)

While patulous eustachian tube can cause autophony:

• It typically presents with autophony that varies with position (worse standing, better lying down) 1
• Hearing loss is not a prominent feature 1
• The combination of hearing loss, tinnitus, and autophony together is more consistent with a third-window lesion 5

Diagnostic Algorithm

Immediate Next Steps

1. Obtain formal audiometry to characterize the hearing loss pattern—SSCD typically shows low-frequency conductive hearing loss with supranormal bone conduction thresholds (bone conduction better than 0 dB) 4

2. Perform tuning fork testing (Weber and Rinne) to confirm conductive component—Weber should lateralize to the affected ear 4, 7

3. Order high-resolution CT of temporal bones with thin cuts (0.5-0.625 mm) reformatted in the plane of the superior semicircular canal to visualize the dehiscence 6, 5

Confirmatory Testing

• Vestibular evoked myogenic potentials (VEMP) show reduced thresholds and increased amplitudes in SSCD 5
• CT imaging demonstrating bony dehiscence between the superior semicircular canal and middle cranial fossa confirms the diagnosis 5

Critical Clinical Pitfalls

• Do not assume conductive hearing loss with normal tympanic membrane is always otosclerosis—the preserved stapedial reflex should prompt consideration of alternative diagnoses 2, 3

• Do not dismiss autophony as a minor symptom—it is a key diagnostic clue for third-window lesions including SSCD and cochlear-facial dehiscence 1, 5

• Do not delay imaging when clinical suspicion is high—HRCT has diagnostic sensitivity of 33.8-87.1% for unexplained conductive hearing loss, and surgical repair can provide excellent outcomes 6