The Carhart notch in otosclerosis is a characteristic dip in bone conduction at 2000 Hz. The mechanism of this notch is:
- A A mechanical artefact due to loss of the inertial component of bone conduction caused by stapes fixation, not true SNHL ✓
- B True sensorineural damage to cochlear hair cells at the 2000 Hz frequency region by advancing cochlear otosclerosis
- C Inflammatory damage to the round window membrane specifically at resonant frequencies
- D Cochlear hydrops secondary to sodium-fluoride deposition in the spiral ligament
Explanation
The Carhart notch (reduction in bone conduction threshold by approximately 5 dB at 500 Hz, 10 dB at 1000 Hz, 15 dB at 2000 Hz, and 5 dB at 4000 Hz, with the dip greatest at 2000 Hz) is a MECHANICAL artefact, not true sensorineural hearing loss. Bone-conducted sound normally reaches the cochlea partly by inertia of the ossicular chain; stapes fixation eliminates this contribution, reducing the apparent bone conduction threshold at frequencies matching the stapes resonant frequency (~2000 Hz). After successful stapedectomy, the Carhart notch largely resolves — confirming its mechanical origin.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.