Accessory Nerve Course — MFDS Part 1 MCQ

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ModerateAnatomy (Head & Neck)Accessory Nerve CourseMFDS Part 1

Which triangle of the neck contains the clinically vulnerable superficial segment of the spinal accessory nerve as it passes from sternocleidomastoid towards trapezius?

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Correct answer: A — Posterior triangle

The correct answer is A, the posterior triangle. After supplying sternocleidomastoid, the spinal accessory nerve emerges near its posterior border and crosses the posterior triangle relatively superficially before entering trapezius. This segment is particularly vulnerable during cervical lymph-node biopsy or neck dissection. Injury typically causes trapezius weakness, shoulder droop, reduced shoulder shrug and impaired elevation or abduction of the arm above the horizontal. The accessory nerve has proximal relations in the upper anterior neck, making the original unqualified wording potentially ambiguous. However, the specified superficial segment between sternocleidomastoid and trapezius is in the posterior triangle, not the anterior triangle or its submental, carotid or digastric subdivisions.

Reference: Koliarakis I, Manatakis DK, Tsitsipanis C, et al. Spinal accessory nerve anatomy in the posterior cervical triangle: A systematic review with meta-analysis. Clinical Anatomy. 2024;37(1):130-139. https://pubmed.ncbi.nlm.nih.gov/37767816/