In acoustic neuroma, cranial nerve to be involved earliest is –

**Core Concept**
Acoustic neuroma, also known as vestibular schwannoma, is a benign tumor arising from the Schwann cells of the vestibulocochlear nerve (cranial nerve VIII). It can cause various neurological symptoms due to compression of adjacent cranial nerves.

**Why the Correct Answer is Right**
The earliest cranial nerve to be involved in acoustic neuroma is typically the VIIth (facial) nerve, due to its close proximity to the vestibulocochlear nerve. As the tumor grows, it can compress the facial nerve, leading to symptoms such as facial weakness, numbness, or changes in taste. The facial nerve is also responsible for controlling the stapedius muscle in the middle ear, which helps regulate sound.

**Why Each Wrong Option is Incorrect**
**Option A:**
* This option is incorrect because the trigeminal nerve (cranial nerve V) is not typically the first cranial nerve to be involved in acoustic neuroma.

**Option B:**
* This option is incorrect because the vagus nerve (cranial nerve X) is not a primary cranial nerve affected by acoustic neuroma.

**Option C:**
* This option is incorrect because the glossopharyngeal nerve (cranial nerve IX) is not typically the first cranial nerve to be involved in acoustic neuroma.

**Clinical Pearl / High-Yield Fact**
In patients with acoustic neuroma, early involvement of the facial nerve can be a critical sign, leading to facial weakness or numbness. This symptom can precede hearing loss and other neurological deficits associated with this condition.

**Correct Answer:** A. Facial nerve.