|The spinal accessory nerve originates from cell bodies located in the cervical spinal cord and brainstem- caudal medulla.Most are located in the spinal cord (1st 4 segments) and ascend through the foramen magnum and exit the cranium through the jugular foramen. They innervate the sternocleidomastoid and trapezius muscles. The nerve is very superficial in the posterior triangle. The lower trapezius may be innervated via 3rd/4th cervical nerve roots thru cervical plexus.
The cranial root of the accessory nerve originates from cells located in the caudal medulla. They are found in the nucleus ambiguus and leave the brainstem with the fibers of the vagus nerve. They join the spinal root to exit the jugular foramen. This superior branch, also known as the accessory or internal branch, joins the vagus either directly or through the ganglion nodosum and then contributes to the pharyngeal, laryngeal, and cardiac sympathetic fibers. Most consider the cranial part of the eleventh cranial nerve to be functionally part of the vagus nerve.
Nerves IX, X, and XI travel together in the jugular foramen. They may be compressed by tumors and aneurysms (Vernet’s syndrome). The XII nerve may also be involved in more extensive lesions occurring in the posterior later-ocondylar space (syndrome of Collet-Sicard); causes include parotid tumors, carotid body tumors, adenopathy of whatever cause, and tuberculosis involving the lymph nodes. Sarcoidosis is another cause. A similar set of etiologies can damage the same four nerves (IX, X, XI, XII) in the posterior retroparotid space (Villaret’s syndrome).
Minor procedures such as posterior triangle lymph node biopsy, cannulation of the internal jugular vein, and carotid endarectomy may damage the nerve. Radiation may damage CN XI.
Weakness (without sensory deficit) presents with scapular winging accentuated with shoulder abduction. Isolated spontaneous neuropathy and stretch injuries have been reported.