A 48-year-old man undergoes excision of the left submandibular gland. The surgeon ligates the facial vein and retracts it superiorly to protect the structures in the floor of the mouth. Postoperatively, he has weakness of the lower lip on the left, with drooping and loss of the labiomental fold when smiling. Which nerve was injured?

• A Nerve to mylohyoid
• B Buccal branch of the facial nerve
• C Cervical branch of the facial nerve
• D Marginal mandibular branch of the facial nerve ✓

Explanation

The marginal mandibular branch runs below the angle and body of the mandible before crossing it to supply depressors of the lip. Retracting the facial vein superiorly keeps this nerve within the raised flap, which is the standard protective manoeuvre. Injury produces ipsilateral lower lip droop without eye closure problems, which excludes the buccal branch. The cervical branch supplies platysma, and the nerve to mylohyoid is motor to mylohyoid and the anterior belly of digastric, neither affecting lip movement.

Reference: Bailey and Love's Short Practice of Surgery, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.