Spinal accessory nerve lesions.

Journal Article (Review)

The spinal accessory nerve, primarily a motor nerve, innervates the sternocleidomastoid and trapezius muscles. Proximally, lesions can occur intracranially at the skull base or just outside the jugular foramen producing ipsilateral weakness of trapezius and sternocleidomastoid muscles; or distally, in the posterior neck triangle causing trapezius muscle weakness.