**Core Concept**
The question tests knowledge of the anatomical pathways of nerves in the neck and their corresponding sensory distributions. Specifically, it involves understanding the **brachial plexus** and its branches. The **medial brachial cutaneous nerve**, a branch of the **medial cord** of the brachial plexus, is responsible for the sensory innervation of the medial aspect of the arm.

**Why the Correct Answer is Right**
The correct answer is related to the nerve that originates from the brachial plexus and provides sensory innervation to the medial side of the arm. The **medial brachial cutaneous nerve** is the specific nerve that supplies this area. Injury to this nerve during a radical neck dissection could result in loss of sensation in the area it innervates.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not correspond to the nerve responsible for the sensory innervation of the medial side of the arm.
**Option B:** Similarly, this option does not match the nerve in question.
**Option D:** This option is also incorrect as it does not relate to the sensory innervation of the medial arm.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **brachial plexus** is formed by the ventral rami of C5-T1 spinal nerves, and its branches are responsible for both motor and sensory functions of the upper limb. The **medial brachial cutaneous nerve** is one such branch, crucial for sensation on the medial aspect of the arm.

**Correct Answer:** C. Medial brachial cutaneous nerve