Marginal Mandibular Nerve — MFDS Part 1 MCQ

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ModerateAnatomy (Head & Neck)Marginal Mandibular NerveMFDS Part 1

Following transcervical removal of a submandibular salivary gland, a patient has weakness of the lower lip on the operated side, producing an asymmetrical smile. Which nerve has most likely been injured?

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Correct answer: E — Marginal mandibular branch of the facial nerve

The correct answer is E. The marginal mandibular branch of the facial nerve crosses the submandibular region and supplies muscles that depress the lower lip. Injury during a transcervical approach can therefore cause ipsilateral lower-lip weakness and an asymmetrical smile. The lingual and hypoglossal nerves are also anatomically at risk during removal of the gland, which made the original stem non-unique. Lingual nerve injury causes altered general sensation in the anterior two-thirds of the tongue, whereas hypoglossal injury causes impaired tongue movement. The buccal facial branch predominantly supplies muscles of the upper lip and cheek, and the inferior alveolar nerve lies within the mandibular canal and is not a characteristic nerve injury from this operation.

Reference: Cambridge University Hospitals NHS Foundation Trust, Removal of submandibular salivary gland, section 'The surgeon tells me that damage to nerves is possible. What does this mean?', approved 18 July 2025. https://www.cuh.nhs.uk/patient-information/removal-of-submandibular-salivary-gland/