Anatomic landmarks for localization of the spinal accessory nerve

Area of Science:

• Anatomy
• Surgical Anatomy
• Neuroanatomy

Background:

• The spinal accessory nerve (SAN) is critical for head and neck movements.
• Accurate localization of the SAN is essential for safe surgical procedures, particularly in neck dissections.
• Variations in SAN anatomy can pose challenges during surgery.

Purpose of the Study:

• To investigate the anatomical topography and reliable landmarks for spinal accessory nerve (SAN) localization.
• To provide detailed measurements of SAN course and extracranial length.
• To assess the utility of various anatomical structures as surgical guides for the SAN.

Main Methods:

• Anatomical dissection of 40 fresh human cadavers (38 male, 2 female).
• Detailed mapping of the spinal accessory nerve (SAN) from its extracranial exit to its course.
• Measurement of distances between the SAN and key anatomical landmarks, including the atlas transverse process, digastric muscle, sternocleidomastoid muscle, and nerve point.

Main Results:

• The SAN was located anterior to the atlas transverse process in 77.5% of dissections.
• The SAN crossed the posterior belly of the digastric muscle at a mean distance of 1.75 cm from its tendon.
• The SAN traversed the sternocleidomastoid (SCM) muscle between its heads in 45% and deep to it in 55%; it exited superior to the nerve point by a mean of 0.97 cm.

Conclusions:

• The nerve point is a highly reliable landmark for SAN localization in surgical neck dissections.
• The atlas transverse process and digastric muscle can also serve as landmarks, but anatomical variations must be considered.
• The number of lymph nodes associated with the SAN chain shows significant variability.