**Core Concept**
Acoustic neuroma, also known as vestibular schwannoma, is a benign tumor arising from the Schwann cells of the vestibular nerve. Early diagnosis is crucial to prevent potential complications such as hearing loss, tinnitus, and balance disorders. Imaging plays a vital role in diagnosing acoustic neuroma, and the choice of investigation depends on its sensitivity and specificity.

**Why the Correct Answer is Right**
Gadolinium-enhanced MRI is the gold standard for diagnosing acoustic neuroma. The addition of gadolinium, a paramagnetic contrast agent, enhances the visibility of the tumor by increasing the signal intensity on T1-weighted images. This allows for accurate visualization of the tumor's size, location, and relationship to surrounding structures. The high sensitivity and specificity of MRI make it an essential tool for diagnosing acoustic neuroma, especially in cases where the tumor is small or located in the internal auditory canal.

**Why Each Wrong Option is Incorrect**
**Option B:** CT scan is less sensitive than MRI for detecting acoustic neuroma, especially in the early stages. CT scans can also fail to distinguish between the tumor and surrounding bone structures, leading to inaccurate diagnoses.

**Option C:** Audiometric analysis, while useful for assessing hearing loss and balance disorders, is not a diagnostic tool for acoustic neuroma. It can help identify patients at risk but is not sufficient for definitive diagnosis.

**Option D:** PET scan is not typically used for diagnosing acoustic neuroma. While it can provide information on metabolic activity, it is not as sensitive as MRI for detecting small tumors or those located in the internal auditory canal.

**Clinical Pearl / High-Yield Fact**
When interpreting MRI scans for acoustic neuroma, it's essential to look for the "dot-in-the-canal" sign, which refers to the small, rounded appearance of the tumor within the internal auditory canal.

**✓ Correct Answer: A. Gadolinium enhanced MRI**