**Core Concept**
A vestibular schwannoma, also known as acoustic neuroma, is a benign tumor arising from the Schwann cells of the vestibular nerve. The earliest symptoms are often related to the compression of adjacent structures, particularly the vestibular nerve, leading to balance and hearing disturbances.

**Why the Correct Answer is Right**
The correct answer is related to the earliest manifestation of vestibular nerve compression, which is typically a feeling of imbalance or dizziness. This symptom arises due to the disruption of normal vestibular function, leading to an inability to maintain balance. The vestibular nerve plays a crucial role in transmitting information about head position and movement to the brain, and its compression can cause symptoms such as vertigo, which is a sensation of spinning or feeling unsteady.

**Why Each Wrong Option is Incorrect**
**Option A:** Hearing loss is a common symptom of acoustic neuroma, but it is not typically the earliest symptom. Hearing loss usually occurs as the tumor grows and compresses the auditory nerve.
**Option B:** Facial weakness or numbness can occur in advanced cases of acoustic neuroma, but it is not the earliest symptom. This symptom is related to the compression of the facial nerve, which is located adjacent to the vestibular nerve.
**Option C:** Headache can occur in various conditions, including acoustic neuroma, but it is not a specific or early symptom of this tumor. Headache is a non-specific symptom that can have many causes.

**Clinical Pearl / High-Yield Fact**
The earliest symptoms of acoustic neuroma are often subtle and may be mistaken for other conditions. A high index of suspicion is necessary for early diagnosis, particularly in patients with a history of radiation exposure or genetic predisposition.

**Correct Answer:** C.