**Question:** Unilateral sensorineural hearing loss may occur in

A. Bacterial meningitis
B. Viral meningitis
C. Acoustic neuroma
D. Otosclerosis

**Core Concept:** Sensorineural hearing loss is a type of hearing loss caused by damage to the sensory hair cells, spiral ganglion neurons, or auditory nerve in the inner ear. It can be conductive or sensorineural in nature. Unilateral sensorineural hearing loss refers to hearing loss in one ear only.

**Why the Correct Answer is Right:** C. Acoustic neuroma is a benign tumor of the vestibulocochlear nerve (cranial nerve VIII). This tumor can compress the nerve, leading to sensorineural hearing loss in the affected ear. The other options are not specific causes of unilateral sensorineural hearing loss:

1. B. Viral meningitis: While meningitis can cause neurological symptoms, it usually does not cause sensorineural hearing loss as the auditory system is not directly infected or affected by the virus.
2. A. Bacterial meningitis: Similar to viral meningitis, bacterial meningitis does not directly affect the auditory system, leading to sensorineural hearing loss.
3. D. Otosclerosis: Otosclerosis is a disease that affects the ossicles in the middle ear, causing conductive hearing loss but not sensorineural hearing loss.

**Why Each Wrong Option is Incorrect:**

A. Bacterial meningitis and viral meningitis are general terms for infections of the meninges, which are the protective membranes covering the brain and spinal cord. These conditions primarily affect the nervous system and can cause neurological symptoms but are not directly associated with sensorineural hearing loss.

B. Bacterial and viral meningitis are conditions affecting the meninges, not the auditory system. They primarily cause neurological symptoms but do not directly lead to sensorineural hearing loss.

C. Otosclerosis affects the ossicles in the middle ear, causing conductive hearing loss but not sensorineural hearing loss. Otosclerosis is a condition that causes issues in the transmission of sound waves through the ossicles, resulting in a blockage or impedance in the transmission of sound waves, causing conductive hearing loss. In contrast, sensorineural hearing loss is caused by damage to the inner ear structures (cochlea, vestibular apparatus, or auditory nerve) and results in a problem with the transmission of sensory signals to the brain. Otosclerosis primarily affects the middle ear and not the inner ear structures, making it different from sensorineural hearing loss.

**Clinical Pearls:**

1. Otosclerosis can lead to conductive hearing loss, but not sensorineural hearing loss.
2. The distinction between conductive and sensorineural hearing loss is crucial in diagnosing and managing patients with hearing loss.
3. Otosclerosis and sensorineural hearing loss can coexist in some cases, as the patient may have conductive and sensorineural components due to the involvement of the middle ear and inner ear, respectively.