Accessory Nerve

nervus accessorius (CN XI)

The spinal accessory nerve (cranial nerve XI) supplies the sternocleidomastoid and trapezius, both of which are tested in the neurological examination of CN XI. Its superficial course through the posterior triangle of the neck makes it vulnerable to injury during posterior triangle lymph node biopsy, neck dissection, and internal jugular vein cannulation, producing the most common iatrogenic peripheral nerve injury in the neck.

Region: Neck

Anatomical Data

Origin, Insertion & Supply

Origin	Cranial nerve XI arising from the lower brainstem and upper cervical cord

Clinical Relevance

Clinical Notes

Accessory nerve injury during posterior triangle procedures produces trapezius paralysis with dropped shoulder, scapular winging (superior angle lifting more than inferior), and inability to shrug or elevate the arm above 90 degrees against resistance. Shoulder pain and functional disability from trapezius loss can be severe and persistent. Immediate surgical repair or reconstruction with donor nerve gives the best results when injury is identified promptly.

Pathology

Common Injuries & Conditions

Accessory Nerve Palsy

Trapezius paralysis from iatrogenic posterior triangle nerve injury producing dropped shoulder, lateral scapular winging, and severely limited arm elevation managed with early nerve repair or reconstruction.