High-resolution ultrasound imaging of the spinal accessory nerve and associated injuries based on a prospective normative study and retrospective analysis.

This study assessed the feasibility of high-resolution ultrasound (HRUS) for visualizing the cervical spinal accessory nerve (SAN) and explored its sonographic characteristics, anatomical landmarks, and normative diameter measurements. A prospective study was conducted in 60 healthy volunteers, in whom the SAN was categorized into three segments: between the trapezius and levator scapulae (S1), from the surface of the levator scapulae to the posterior border of the sternocleidomastoid muscle (SCM) (S2), and from the posterior border of the SCM to the upper cervical region (S3). HRUS was utilized to evaluate SAN visibility and measure the maximum short-axis diameter (SD), with normative values statistically analyzed. In addition, a retrospective analysis was performed in 12 patients with clinically and electrophysiologically confirmed SAN injury to characterize sonographic abnormalities. HRUS successfully delineated the SAN and adjacent structures with a 100% visibility rate across all segments. No significant differences in SD were observed between sides, segments, or sexes, though SD exhibited a positive correlation with body mass index (BMI). In patients with SAN injury, HRUS identified complete nerve rupture, with all cases presenting trapezius muscle atrophy. These findings establish HRUS as a reliable, non-invasive imaging modality for assessing SAN morphology and diagnosing nerve injuries.