Identification of three anatomical patterns of the spinal accessory nerve in the neck by neurophysiological mapping.

Background: In spite of preservation of the accessory nerve there is still considerable proportion of patients with partial nerve damage during modified radical neck dissection (MRND).

Methods: The nerve was identified during the surgery and its branches for the trapezius muscle mapped with nerve monitor.

Results: The accessory nerve was mapped during 74 hemineck dissections and three patterns were identified. In type 1 nerve exits at the posterior end of the sternocleidomastoid muscle (SCm) and then it enters the level V (66%). In type 2 the nerve for trapezius muscle branches off before entering the SCm (22%). In type 3 the nerve exits at the posterior part of the SCm and it joins to the cervical plexus (12%). The nerve than exits this junction more medially as a single trapezius branch.

Conclusions: The description of three anatomical patterns in level II and V could help preserving the trapezius branch during MRND.