Carhart's notch on audiometry in otosclerosis is a sensorineural dip seen at which frequency and is caused by:
- A 4000 Hz; cochlear damage from abnormal bone adjacent to basal turn
- B 500 Hz; low-frequency sensorineural component from endolymphatic hydrops
- C 2000 Hz; mechanical resonance of the ossicular chain transmitted to the cochlea via bone conduction ✓
- D 1000 Hz; pure neural degeneration from chronic fixation
Correct answer: C. 2000 Hz; mechanical resonance of the ossicular chain transmitted to the cochlea via bone conduction
Explanation
Carhart's notch is a mechanical artefact seen at 2000 Hz on bone-conduction audiometry in otosclerosis; it occurs because the normal 2000 Hz resonant frequency of the ossicular chain (which contributes to bone-conduction measurement) is lost when the stapes is fixed. After successful stapedectomy, the Carhart's notch disappears, confirming its mechanical rather than sensorineural nature. This is a distinguishing feature of stapedial otosclerosis.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.