Different branching patterns of the spinal accessory nerve: impact on neck dissection technique and postoperative shoulder function.

PURPOSE OF REVIEW: Despite nerve-sparing surgery, postoperative shoulder morbidity remains high and significantly impacts patient's quality of life. This review will focus on recent findings of anatomical nuances of the cranial nerve XI (CN XI) along its course in the neck and possible reasons for postoperative morbidity.

RECENT FINDINGS: The most recent studies identified three different branching patterns of the CN XI in the neck. In type 1 (66%), the branch for trapezius muscle exits at the posterior border of the sternocleidomastoid muscle (mSCM). In type 2 (22%), the branch for trapezius muscle takes off from the common trunk of the CN XI before it enters the mSCM. In type 3 (12%), the motor branch for trapezius muscle exits behind posterior border of mSCM but takes a more medial course to form macroganglia with cervical nerves. Cervical nerves may also contribute to innervation of the trapezius muscle in up to 39% of the cases, but the clinical importance of those connections is not known.

SUMMARY: If these anatomical patterns are not recognized and if cervical nerves are resected during neck dissection, shoulder morbidity remains high. The role of cervical nerves in innervation of the trapezius muscle is still controversial and unpredictable.