Ultrasound imaging of the spinal accessory nerve in the neck.

INTRODUCTION: The spinal accessory nerve is the external terminal division of the 11th cranial nerve which passes postero-inferiorly in the neck, innervating the sternocleidomastoid and trapezius muscles. The spinal accessory nerve is often in the field of view of neck ultrasound imaging, however, can be overlooked and underappreciated during sonographic neck imaging and ultrasound-guided lymph node biopsies.

METHOD: A scoping review of the literature was conducted to assess current knowledge regarding sonographic imaging of the spinal accessory nerve. The authors' sonographic experience and practical sonographic workshops informed the development of a sonographic technique to image this nerve.

FINDINGS: Iatrogenic injury is a common cause of spinal accessory neuropathy, particularly from needle biopsies of neck lymph nodes and surgery. Ultrasound imaging can effectively demonstrate the extracranial component of the spinal accessory nerve.

DISCUSSION: An appreciation of the anatomy and path of the spinal accessory nerve is important to ensure appropriate sonographic identification of the spinal accessory nerve and ensure it is not in the needle path during ultrasound-guided neck lymph node biopsies. In addition, ultrasound imaging can be used to diagnose spinal accessory nerve injury, pathology and subsequent denervation of the sternocleidomastoid and trapezius muscles which can affect neck and shoulder pain and mobility, negatively impacting daily activities.

CONCLUSION: Awareness of the spinal accessory nerve anatomy and imaging appearances is required when sonographically imaging the neck to identify the spinal accessory nerve, ensuring it is not in the needle path during ultrasound-guided neck biopsies and identifying any potential injury or pathological involvement.