In stapedectomy for otosclerosis, the Carhart notch is a characteristic audiometric finding. It refers to a dip in bone conduction thresholds at:
- A 250 Hz due to increased stiffness of the ossicular chain
- B 4000 Hz due to noise-induced cochlear damage
- C 2000 Hz due to loss of inertial bone conduction component ✓
- D 500 Hz due to resonance of the tympanic membrane
Correct answer: C. 2000 Hz due to loss of inertial bone conduction component
Explanation
The Carhart notch is a mechanical artefact in otosclerosis where bone conduction thresholds show an apparent depression of 5–10 dB at 2000 Hz. This occurs because the fixation of the stapes abolishes the inertial component of bone conduction that normally occurs at 2000 Hz. It is NOT true cochlear SNHL; it disappears after successful stapedectomy when ossicular chain mobility is restored. A notch at 4000 Hz is characteristic of noise-induced hearing loss (NIHL).
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.