Surface-Based Localization of the Spinal Accessory Nerve in the Posterior Triangle: A High-Volume Cadaveric Study...

The spinal accessory nerve (SAN) is particularly vulnerable to iatrogenic injury during head and neck procedures, especially in the posterior cervical triangle where it courses superficially. Despite its clinical relevance, reliable surface-based strategies for SAN localization remain underdeveloped, particularly in the context of aesthetic and limited-access surgeries.

A cadaveric study was conducted on 186 hemi-necks from 111 Thiel-embalmed cadavers to identify consistent anatomical relationships between the SAN and four readily palpable skeletal landmarks: the mastoid process, sternoclavicular joint, midclavicular point, and acromioclavicular joint. Linear distances from the SAN's emergence at the posterior border of the sternocleidomastoid muscle to each landmark were measured, and a reproducible "danger zone" was mathematically defined.

The SAN was reliably identified in all dissections. The mean distances from the nerve to the mastoid process, sternoclavicular joint, midclavicular point, and acromioclavicular joint were 5.1 cm, 11.0 cm, 9.1 cm, and 12.8 cm, respectively. A circular danger zone with a mean diameter of 2.96 cm (6.9 cm² area) was calculated based on overlapping standard deviations. When focusing solely on the mastoid process as the most consistent reference, a refined zone of 1.98 cm diameter (3.1 cm²) was delineated.

This study defines a clinically relevant and reproducible surface-based danger zone for SAN localization in the posterior cervical triangle. Anchored to palpable skeletal landmarks and validated on a large anatomical dataset, the proposed model enhances surgical safety during oncologic and aesthetic neck procedures by facilitating preemptive nerve identification.