Study of the Anatomical Variations of Spinal Accessory Nerve Seen During Neck Dissection

Area of Science:

• Anatomy
• Head and Neck Surgery
• Neuroanatomy

Background:

• The spinal accessory nerve (SAN) is crucial for shoulder function and is often encountered during neck dissections for head and neck cancers.
• Understanding anatomical variations of the SAN is vital for surgeons to prevent iatrogenic injury and subsequent shoulder dysfunction.

Purpose of the Study:

• To document anatomical variations of the SAN during neck dissections.
• To correlate SAN course and branching with anatomical landmarks and patient biometrics (neck length, height).

Main Methods:

• Thirty-one neck dissections were performed on 30 patients undergoing treatment for head and neck cancers.
• The course and branching of the SAN were meticulously studied in relation to the internal jugular vein (IJV), sternocleidomastoid (SCM) muscle, greater auricular point (GAP), mastoid process, clavicle, and angle of the mandible.
• Correlation with patient neck length and height was analyzed.

Main Results:

• The SAN was found ventral to the IJV in 67.7% of cases and dorsal in 32.3% at the posterior belly of digastric muscle level.
• The SAN consistently emerged cephalic to the GAP at the posterior SCM border (mean distance: 1.72 ± 0.54 cm).
• A positive correlation was observed between SAN parameters and patient neck length/height, with the exit point being inferior in longer necks/taller patients.

Conclusions:

• The greater auricular point (GAP) is the most reliable landmark for SAN localization, followed by the mastoid process and angle of the mandible.
• Surgeons must be aware of SAN variations, particularly its relationship with the IJV and branching patterns.
• Knowledge of these variations aids in preventing shoulder syndrome and potential medicolegal issues.