**Core Concept**
Adenoid cystic carcinoma is a malignant salivary gland tumor known for its aggressive behavior, including perineural invasion along nerve sheaths. This characteristic makes it challenging to treat and manage, often leading to recurrence and metastasis.

**Why the Correct Answer is Right**
Adenoid cystic carcinoma exhibits a distinct pattern of growth, where it invades and spreads along the nerve sheath. This is due to its neurotrophic properties, allowing it to adhere to and migrate along nerve fibers. The tumor's ability to invade nerve sheaths is a hallmark of its malignant potential and is often associated with a poorer prognosis. The tumor's growth along nerve sheaths can lead to numbness, pain, or other neurological symptoms, making it a significant clinical concern.

**Why Each Wrong Option is Incorrect**
**Option A:** Pleomorphic adenoma is the most common type of salivary gland tumor, but it is typically benign and does not exhibit perineural invasion. While it can grow to a large size, it generally does not spread along nerve sheaths.
**Option B:** Mucoepidermoid carcinoma is a malignant salivary gland tumor, but it is more commonly associated with local destruction and bone invasion rather than perineural invasion along nerve sheaths.
**Option D:** Warthin's tumor is a benign salivary gland tumor that is often associated with smoking and is characterized by its lymphoid stroma. It does not exhibit perineural invasion and is not typically aggressive.

**Clinical Pearl / High-Yield Fact**
Adenoid cystic carcinoma is often referred to as a "tumor of the nerve" due to its characteristic perineural invasion. This unique behavior makes it a challenging tumor to manage, and early recognition is essential for optimal treatment outcomes.

**✓ Correct Answer: C. Adenoid cystic carcinoma**