Which nerve is most vulnerable to injury during surgery of the parotid gland region and at the inferior border of the mandible?

Correct answer: C. Marginal mandibular branch of the facial nerve

• A. Incorrect. The great auricular nerve (C2–C3) is frequently sacrificed during parotidectomy, causing numbness of the earlobe — an accepted sensory consequence, but not the feared MOTOR injury.
• B. Incorrect. The maxillary division (V2) is a sensory nerve of the midface located deep in the pterygopalatine fossa — nowhere near the surgical field of parotid or submandibular surgery.
• C. Correct. The MARGINAL MANDIBULAR branch of CN VII is the most commonly injured branch in this region. It runs superficially, often DIPPING BELOW the inferior border of the mandible as it crosses the facial vessels, and is covered only by skin, subcutaneous tissue and platysma. Injury produces an asymmetric lower lip on smiling because the depressor anguli oris and depressor labii inferioris are paralysed. This is also why submandibular incisions are placed at least 2 cm below the mandibular border.
• D. Incorrect. The buccal branch of CN VII can be injured, but it has substantial cross-innervation with adjacent branches, so isolated injury is often subclinical. The marginal mandibular branch has minimal cross-innervation and its deficits are permanent and visible.