A pathological process affecting the eleventh cranial nerve.
Supranuclear lesions of the accessory nerve result in mild, usually transient, dysfunction of function of the sternocleidomastoid and trapezius muscles, due to the bilateral innervation. In the spinal cord the nuclei of the eleventh cranial nerve can be affected by amyotrophic lateral sclerosis (ALS), syringomyelia, polio, and intraspinal tumors. Occlusion of the vertebral or posterior inferior cerebellar artery produces infarction of the medullary tegmentum, with deficits of V, IX, X, and XI (Wallenberg’s syndrome). The accessory nerve is also vulnerable to space occupying lesions as it travels down the jugular foramen (vernetâ€™s syndrome)
Observe the mass and contour of the sternocleidomastoid muscles as the patient looks ahead. Test the right sternocleidomastoid muscle by facing the patient and placing your right palm laterally on the patient’s left cheek. Instruct the patient to turn the head to the left, resisting the pressure you are exerting in the opposite direction. At the same time, observe and palpate the right sternocleidomastoid with your left hand. Then reverse the procedure to test the left sternocleidomastoid.
Continue to test the sternocleidomastoid by placing your hand on the patient’s forehead and pushing backward as the patient pushes forward. Observe and palpate the sternocleidomastoid muscles.
Now test the trapezius. Ask the patient to face away from you and observe the shoulder contour for atrophy, displacement, or winging of the scapula. Observe for drooping of the shoulder. Place your hands on the patient’s shoulders and press down as the patient elevates or shrugs the shoulders and then retracts the shoulders.