Carharts notch in audiogram is deepest frequency of –
**Core Concept**
Carhart's notch is a characteristic finding in the audiogram of patients with otosclerosis, a type of bone dysplasia affecting the middle ear. It is a depression or notch in the bone conduction threshold at a specific frequency, usually between 2,000 and 4,000 Hz.
**Why the Correct Answer is Right**
Carhart's notch is caused by the fixation of the stapes bone in the middle ear due to otosclerosis. This fixation leads to a reduction in the mobility of the stapes, resulting in a decrease in the bone conduction threshold at the affected frequency. The stapes is responsible for transmitting sound vibrations from the incus to the inner ear. When it is fixed, the transmission of sound is impaired, resulting in a characteristic notch in the audiogram. The frequency at which the notch is deepest typically ranges from 2,000 to 4,000 Hz, with the maximum depression usually occurring at 2,000 Hz.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Carhart's notch is not a feature of noise-induced hearing loss, which typically affects higher frequencies.
**Option B:** This option is incorrect because Carhart's notch is not a feature of sensorineural hearing loss, which typically affects high-frequency sounds.
**Option C:** This option is incorrect because Carhart's notch is not a feature of conductive hearing loss in general, which can result from various causes such as otitis media or a perforated eardrum.
**Clinical Pearl / High-Yield Fact**
Carhart's notch is a classic finding in otosclerosis and is often used as a diagnostic clue. It is essential to recognize this sign in the audiogram to differentiate otosclerosis from other types of hearing loss.
**Correct Answer:** C. 2,000 Hz