A 68-year-old man has many months history of progressive hearing loss, unsteady gait, tinnitus, and facial pain. An MRI scan reveals a tumor at the cerebellopontine angle. Which of the following cranial nerves is this tumor most likely to affect?
**Core Concept**
The cerebellopontine angle (CPA) is a critical anatomical location where multiple cranial nerves converge. The CPA is a narrow space between the cerebellum and the pons, and tumors in this region can compress or damage nearby cranial nerves, leading to various neurological symptoms.
**Why the Correct Answer is Right**
The tumor at the CPA is most likely to affect the **Vestibulocochlear nerve (CN VIII)**, also known as the auditory or acoustic nerve. This nerve is responsible for transmitting sound and balance information from the inner ear to the brain. The symptoms described, such as progressive hearing loss, tinnitus, and unsteady gait, are classic presentations of vestibulocochlear nerve dysfunction. The facial pain may be due to involvement of the trigeminal nerve (CN V), but this is less likely.
**Why Each Wrong Option is Incorrect**
**Option A:** The **Trigeminal nerve (CN V)** is responsible for facial sensation and motor functions, but it is not typically affected by tumors at the CPA. While CN V may be involved in cases of CPA tumors, it is not the most likely nerve to be affected.
**Option B:** The **Glossopharyngeal nerve (CN IX)** is involved in swallowing, taste, and parasympathetic functions, but it is not typically affected by CPA tumors. CN IX may be involved in cases of CPA tumors, but it is not the most likely nerve to be affected.
**Option C:** The **Facial nerve (CN VII)** is responsible for facial motor functions and taste, but it is not typically affected by CPA tumors. While CN VII may be involved in cases of CPA tumors, it is not the most likely nerve to be affected.
**Clinical Pearl / High-Yield Fact**
CPA tumors, particularly acoustic neuromas, can cause a triad of symptoms: progressive hearing loss, tinnitus, and unsteady gait. These symptoms are due to compression of the vestibulocochlear nerve and the cerebellum, respectively.
**Correct Answer:** C. Facial nerve (CN VII)