**Core Concept**
Acoustic neuroma, a type of benign tumor, arises from the Schwann cells of the vestibulocochlear nerve (cranial nerve VIII). This growth can lead to compression of adjacent neural structures, resulting in various symptoms. The most prominent symptom is related to the involvement of the cochlear division of the vestibulocochlear nerve.

**Why the Correct Answer is Right**
The most common symptom of acoustic neuroma is unilateral sensorineural hearing loss, specifically affecting the high-frequency range. This occurs due to the compression of the cochlear nerve, leading to impaired sound conduction. The tumor's growth can also affect the vestibular division, causing balance disturbances, but hearing loss is the most prominent symptom.

**Why Each Wrong Option is Incorrect**
**Option A:** Tinnitus is a symptom of acoustic neuroma, but it is not the most prominent symptom. While tinnitus can be present, it is often accompanied by hearing loss.
**Option B:** Ataxia is a symptom of cerebellar lesions or damage to the vestibular system, not typically associated with acoustic neuroma. Ataxia involves coordination and balance issues.
**Option C:** Facial weakness is a symptom of facial nerve (cranial nerve VII) involvement, not typically associated with acoustic neuroma.
**Option D:** Headache is a nonspecific symptom that can be associated with various conditions, including acoustic neuroma, but it is not the most prominent symptom.

**Clinical Pearl / High-Yield Fact**
A classic "red flag" for acoustic neuroma is the presence of unilateral sensorineural hearing loss, especially in the high-frequency range, particularly in patients over 50 years old.

**Correct Answer:** C. Facial weakness is a symptom of facial nerve (cranial nerve VII) involvement, not typically associated with acoustic neuroma.