Carhart Notch — Otosclerosis Stage III MCQ — NEET PG Practice Question | NEETPGAI
Carhart Notch — Otosclerosis Stage III
medium
ear ENT
A 32-year-old woman presents with progressive bilateral hearing loss over 5 years and paracusis of Willis. Audiometry shows a conductive hearing loss with an air-bone gap. The structure marked **A** in the diagram shows a characteristic 15-20 dB depression of bone conduction thresholds at 2 kHz. Tympanometry is type As with absent acoustic reflexes bilaterally. What is the pathophysiological basis of this finding, and what would be the expected change in bone conduction at 2 kHz following successful stapedotomy?
A. True sensorineural cochlear loss at 2 kHz due to otosclerotic involvement of the cochlear capsule; bone conduction remains depressed post-operatively
B. Eustachian tube dysfunction reducing the stiffness of the middle ear; bone conduction improves only at frequencies >4 kHz
C. Ossicular chain discontinuity causing resonant frequency shift to 4 kHz; bone conduction worsens further after stapedotomy
D. Mechanical disruption of the inertial component of bone conduction by stapedial fixation; bone conduction improves by 10-15 dB at 2 kHz post-operatively
Explanation
Why option 1 is right
The Carhart notch is a mechanical artifact of bone conduction audiometry, NOT true cochlear hearing loss. In otosclerosis with stapedial fixation, the fixed stapes footplate disrupts the normal inertial component of bone conduction transmission at the resonant frequency of the ossicular chain (~2 kHz), causing bone conduction thresholds to appear 15-20 dB worse than the actual cochlear reserve. This is the crucial clinical implication: the notch is reversible. After successful stapedotomy (creation of a small fenestra in the footplate with piston prosthesis placement), the stapes regains mechanical mobility, restoring normal bone conduction transmission, and bone conduction improves by 10-15 dB at 2 kHz, revealing the true cochlear reserve (Dhingra ENT 7e; Cummings Otolaryngology).
Why each distractor is wrong
Option 2: Misrepresents the Carhart notch as true sensorineural cochlear loss. The anchor fact explicitly states it is NOT a true cochlear hearing loss; it is mechanical. If it were true cochlear damage, it would NOT resolve post-operatively, but the clinical anchor states it DOES resolve after stapedotomy.
Option 3: Incorrectly suggests ossicular chain discontinuity and a shift of resonant frequency to 4 kHz. Otosclerosis causes stapes fixation (not discontinuity), and the resonant frequency is at 2 kHz, not 4 kHz. Stapedotomy improves bone conduction; it does not worsen it.
Option 4: Confuses the mechanism with Eustachian tube dysfunction, which does not cause a Carhart notch. The Carhart notch is specific to stapedial fixation, not tube dysfunction, and the frequency-specific improvement post-operatively is at 2 kHz, not >4 kHz.
High-YieldNEET PG
Carhart notch = mechanical artifact at 2 kHz in otosclerosis; resolves 10-15 dB after stapedotomy, proving it is NOT true cochlear loss.
Dhingra ENT 7e; Cummings Otolaryngology
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