Carhart’s notch in audiogram is deepest at the frequency of:
**Core Concept**
Carhart's notch is a characteristic audiometric phenomenon observed in patients with otosclerosis, a type of bone growth in the middle ear. It is characterized by a distinct dip or notch in the bone conduction threshold at a specific frequency, which is a key diagnostic clue for otosclerosis.
**Why the Correct Answer is Right**
Carhart's notch is typically deepest at 2000 Hz, which is the frequency most commonly affected by otosclerosis. This is because the bone growth in otosclerosis often involves the stapes bone, which is responsible for transmitting sound vibrations to the inner ear at this frequency. The stapes bone is most affected at 2000 Hz, leading to a characteristic notch in the bone conduction threshold. This is because the abnormal bone growth in otosclerosis causes a mechanical impedance mismatch, leading to a decrease in sound transmission at this frequency.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the notch is not typically deepest at 1000 Hz, which is a lower frequency and less commonly affected by otosclerosis.
**Option B:** This option is incorrect because the notch is not typically deepest at 4000 Hz, which is a higher frequency and not as commonly affected by otosclerosis.
**Option C:** This option is incorrect because the notch is not typically deepest at 8000 Hz, which is an even higher frequency and not relevant to the characteristic audiometric findings in otosclerosis.
**Clinical Pearl / High-Yield Fact**
Remember that Carhart's notch is a key diagnostic clue for otosclerosis, and it is typically deepest at 2000 Hz. This is a classic exam question, and being able to recall this detail can help you diagnose otosclerosis correctly.
**Correct Answer:** C. 2000 Hz