A 58-year-old man is admitted to the emergency department with progressive unilateral hearing loss and ringing in the affected ear (tinnitus) of 4 months’ duration. Radiographic examination reveals a tumor at the cerebellopontine angle. Which of the following nerves is most likely affected?
**Core Concept**
The cerebellopontine angle (CPA) is a critical anatomical location where several cranial nerves converge. A tumor at this site can compress or damage nearby nerves, leading to various symptoms. In this case, the patient presents with hearing loss and tinnitus, suggesting involvement of a nerve responsible for auditory function.
**Why the Correct Answer is Right**
The cerebellopontine angle is a common location for vestibular schwannomas, also known as acoustic neuromas. These benign tumors arise from the Schwann cells of the vestibulocochlear nerve (CN VIII). Compression of CN VIII can lead to sensorineural hearing loss, tinnitus, and balance problems. The vestibulocochlear nerve is responsible for transmitting sound and balance information from the inner ear to the brain.
**Why Each Wrong Option is Incorrect**
**Option A:** The trigeminal nerve (CN V) is primarily responsible for facial sensation and motor function. While it does pass through the CPA, it is not the primary nerve involved in hearing and balance.
**Option B:** The facial nerve (CN VII) controls facial expression and taste. It also passes through the CPA but is not directly responsible for hearing and balance.
**Option C:** The glossopharyngeal nerve (CN IX) is involved in swallowing and taste. It does not play a significant role in auditory function.
**Option D:** The vagus nerve (CN X) is responsible for various functions, including swallowing and parasympathetic innervation of the head and neck. It is not directly involved in hearing and balance.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that tumors at the cerebellopontine angle often present with a triad of symptoms: hearing loss, tinnitus, and balance problems. This classic presentation should raise suspicion for a vestibular schwannoma or other CPA tumors.
**Correct Answer:** C. Vestibulocochlear nerve (CN VIII).