Accessory Nerve Injury

Excerpt

The cranial nerves are twelve pairs that travel outside the skull via foramina to innervate various structures. Cranial nerve (CN) XI is also known as the accessory nerve (see Image. The Accessory Nerve). According to the morphology of the cranial root of the accessory nerve, it is made of the union of 2 to 4 short filaments, making the cranial roots of the accessory nerve. Two to 9 rootlets join the spinal root to form the nerve. The cranial roots of CN XI could be considered part of the vagus nerve when factoring in the function of the 2 nerves. Both the cranial roots of the accessory nerve and the vagus nerve originate from the nucleus ambiguus and dorsal nucleus of the vagus nerve and travel to the laryngeal muscles, supplying the motor fibers (see Image. Muscles of the Head, Face, and Neck).

As the accessory nerve travels down and away from the brain, the cranial and spinal pieces of the nerve come together to form the spinal accessory nerve (SAN). The fusion of cranial and spinal contributions within the skull base forms the spinal accessory nerve. It exits the skull through the jugular foramen adjacent to the vagus nerve. The spinal accessory nerve descends alongside the internal jugular vein, coursing posterior to the styloid process, posterior belly of the digastric muscle, and sternocleidomastoid muscle (SCM) before entering the posterior cervical triangle (see Image. Superficial Neck Anatomy). The accessory nerve leaves the jugular foramen along with the glossopharyngeal nerve (CN IX) and vagus nerve (CN X) (see Image. Dural Venous Sinuses). It travels to the SCM, either superficial or deep, and then enters the trapezius muscle, where a major accessory nerve trunk converges with C2, C3, or both. The traveling pathway of this nerve provides functional significance to the structures in the posterior neck. However, due to its long and superficial nature, the accessory nerve is prone to injury. Injury to the accessory nerve could be from blunt trauma, incidental, or, most commonly, iatrogenic reasons.