A 30-year-old woman presents with progressive bilateral hearing loss. Audiometry shows bilateral conductive hearing loss with a characteristic dip at 2000 Hz on bone conduction audiogram. Tympanometry shows Type As (reduced compliance). The pathological process causing this 2000 Hz bone conduction dip is:
- A Sensorineural component from cochlear involvement by otosclerosis
- B Carhart's notch — mechanical artifact due to absent stapes footplate vibration ✓
- C Noise-induced hearing loss at the 4 kHz frequency
- D Direct compression of the round window membrane
Correct answer: B. Carhart's notch — mechanical artifact due to absent stapes footplate vibration
Explanation
Carhart's notch is a characteristic 2000 Hz dip (occasionally 4000 Hz) on the bone conduction audiogram in otosclerosis. It is NOT a true sensorineural loss but rather a mechanical artifact: the fixation of the stapes footplate eliminates its contribution to bone conduction vibration, reducing apparent bone conduction threshold at 2000 Hz. It disappears after successful stapedectomy, confirming its mechanical basis. This differentiates otosclerosis from mixed SNHL. Type As tympanogram (reduced peak compliance) reflects the stiffened ossicular chain.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.