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Digastric Muscle Innervation — MFDS Part 1 MCQ

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HardAnatomy (Head & Neck)Digastric Muscle InnervationMFDS Part 1

Following surgery on the medial aspect of the mandibular ramus, a patient has preserved lower-lip and chin sensation and normal tongue movement. Intraoperative nerve stimulation produces no contraction of the anterior belly of the digastric, although the posterior belly contracts normally. Which nerve was most likely divided before the inferior alveolar nerve entered the mandibular foramen?

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Correct answer: E — Mylohyoid nerve, arising from the inferior alveolar nerve (V3)

The correct answer is E. The anterior belly of the digastric normally receives motor innervation from the mylohyoid nerve, which branches from the inferior alveolar nerve before the latter enters the mandibular foramen. Preserved lower-lip and chin sensation indicates that the main inferior alveolar nerve remains functional distal to this branch. The posterior belly is supplied by the facial nerve, explaining its preserved contraction. The hypoglossal nerve supplies the tongue muscles, whereas C1 fibres travelling with it supply geniohyoid and thyrohyoid. The glossopharyngeal nerve supplies stylopharyngeus. Rare accessory facial innervation of the anterior belly has been described, but it does not alter the usual anatomical supply tested here.

Reference: Choi P, Iwanaga J, Dupont G, Oskouian RJ, Tubbs RS. Clinical anatomy of the nerve to the mylohyoid. Anatomy & Cell Biology. 2019;52(1):12–16. https://pubmed.ncbi.nlm.nih.gov/30984446/