Variations in the Anatomy of the Accessory Nerve in the Posterior Triangle of the Neck: A Multi-Center Dissection Study

International Journal of Anatomy and Physiology | Vol. 15, No. 9, September 2026 | pp. 317–328

DOI: 10.46882/2026/IJAP/000194

Article Type: Original Research Article

Title: Variations in the Anatomy of the Accessory Nerve in the Posterior Triangle of the Neck: A Multi-Center Dissection Study

Names of Authors: Mateusz J. Zeliński¹, Katarzyna A. Nowak²

Authors’ Affiliations: ¹Department of Anatomy, Medical University of Łódź, Łódź, Poland; ²Department of Otolaryngology, Medical University of Silesia, Katowice, Poland

Abstract:
The accessory nerve (CN XI) is vulnerable to iatrogenic injury during cervical lymph node biopsies, neck dissections, and tumor resections within the posterior triangle of the neck. This study aimed to map the anatomical variations, surface landmarks, and exit trajectories of the accessory nerve. One hundred neck halves from fifty formalin-fixed adult cadavers were examined. The distance from the nerve's exit at the posterior border of the sternocleidomastoid muscle (SCM) to the mastoid process tip was measured using digital calipers, and its entry point into the trapezius muscle was localized relative to the clavicle. The mean distance from the mastoid process tip to the nerve’s emergence at the SCM was 42.4 ± 3.8 mm. Upon leaving the SCM, the nerve followed a straight, oblique course in 78.0% of specimens, while a tortuous loop configuration was noted in 22.0%. The nerve entered the anterior border of the trapezius muscle at a mean distance of 51.5 ± 4.2 mm superior to the clavicle. In 6.0% of cases, the nerve bifurcated within the posterior triangle before entering the trapezius. These measurements establish safe surgical margins, emphasizing the need for meticulous identification of the nerve's exit point relative to the mastoid tip to mitigate postoperative shoulder drop.

Keywords: Accessory Nerve, Posterior Triangle, Sternocleidomastoid Muscle, Trapezius, Iatrogenic Injury, Neck Dissection

Manuscript Timeline: Received: July 28, 2026; Revised: September 04, 2026; Accepted: September 16, 2026; Published: September 30, 2026

Citation: Zeliński M.J., & Nowak K.A. (2026). Variations in the Anatomy of the Accessory Nerve in the Posterior Triangle of the Neck: A Multi-Center Dissection Study. International Journal of Anatomy and Physiology, 15(9), 317–328. DOI: 10.46882/2026/IJAP/000194

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