Pure-tone audiometry of a 30 year old field worker shows Carha’s notch. He has the following condition:
**Core Concept**
Carha's notch, also known as Carhart's notch, refers to a characteristic dip in the bone conduction threshold at 2000 Hz in the audiogram of patients with otosclerosis. This condition is characterized by abnormal bone growth in the middle ear, specifically the stapes bone, which can cause conductive hearing loss.
**Why the Correct Answer is Right**
In otosclerosis, the abnormal bone growth leads to fixation of the stapes bone, preventing it from vibrating in response to sound waves. This results in a conductive hearing loss, which is more pronounced at frequencies around 2000 Hz. The characteristic dip in the bone conduction threshold at 2000 Hz, known as Carhart's notch, is a diagnostic feature of otosclerosis. This is because the abnormal bone growth in the middle ear affects the transmission of sound waves, leading to a specific pattern of hearing loss.
**Why Each Wrong Option is Incorrect**
* **Option A:** Otosclerosis is not associated with Meniere's disease, which is characterized by a triad of vertigo, tinnitus, and hearing loss, typically affecting the low-frequency range.
* **Option B:** Carhart's notch is not a characteristic feature of acoustic neuroma, which is a type of benign tumor that affects the eighth cranial nerve and can cause sensorineural hearing loss, particularly in the high-frequency range.
* **Option C:** Otosclerosis is not a type of otitis media, which is an infection of the middle ear that can cause conductive hearing loss, but is typically associated with a history of ear infection and is not characterized by Carhart's notch.
**Clinical Pearl / High-Yield Fact**
Carhart's notch is a classic diagnostic feature of otosclerosis, but it can be absent in some cases. A thorough clinical examination, including otoscopy and tympanometry, is essential to confirm the diagnosis.
**Correct Answer: C. Otosclerosis. Otosclerosis**