Conditions: Weakness of the Spinal Accessory Nerve
(Cranial Nerve XI)
Image modified from: OpenStax College, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
What is the Spinal accessory nerve?
Raising the arm from straight outward horizontal to vertical requires the spinal accessory nerve and trapezius muscle,
The spinal accessory nerve controls two muscles—the sternocleidomastoid and the trapezius muscle. The trapezius muscle allows shrugging the shoulders and raising the arm from a straight outward position to a vertical position. The sternocleidomastoid assists the action of turning the head, and is a normal visible anatomic feature of a thin neck. Each of the left and right spinal accessory nerves exits the skull base along the internal jugular vein, then passes into the sternocleidomastoid muscle, with some branches terminating in this muscle, and other branches passing out of the sternocleidomastoid muscle, across the neck before entering the trapezius muscle.
Why is the spinal accessory nerve affected by surgery?
Injury to the spinal accessory nerve commonly occurs to some extent during neck surgery, particularly in the removal of neck lymph node(s) in procedures called neck dissection (cervical lymphadenectomy) or lymph node biopsy. Spinal accessory nerve dysfunction can also result from cancer growth directly into the nerve, other trauma, and in some causes spontaneously. Damage at any point along the nerve's course will affect the function of the nerve. The nerve may be intentionally removed in certain neck dissection techniques (including the radical neck dissection). Other techniques of removing lymph nodes from the neck may employ attempts to preserve the nerve while still accessing and removing the surrounding lymph nodes.
What are the symptoms of spinal accessory neuropathy?
Interruption of the nerve supply to the sternocleidomastoid muscle may result in atrophy (loss of bulk) in the sternocleidomastoid muscle, which may be cosmetically noticeable. Dysfunction of the trapezius muscle can produce neck pain, inability to move the arm from a straight outward (horizontal) position to a vertical position, a drooping shoulder, protrusion of the shoulder blade (causing a “winged scapula”), and/or a weakness of elevation of the shoulder.
HOw is spinal accessory neuropathy TREATED?
When injury to the spinal accessory nerve occurs due to surgical dissection, recovery and compensation of the injury is best treated with physical therapy. Time alone may allow healing of the nerve, but this may take over one year and physical therapy started shortly after surgery tends to yield the best results.
How much will spinal accessory neuropathy bother someone?
Individual differences account for significant variability in degree of burden from spinal accessory weakness. In general, however, a mild and partial weakness of the spinal accessory nerve may be well tolerated with mild physical limitations, whereas a complete loss of spinal accessory nerve function is more likely to cause pain or physical limitations. Physical therapy usually helps minimize the problems associated with spinal accessory injury.