Anatomical Variant of Spinal Accessory Nerve Passing through Fenestrated Internal Jugular Vein

Neck dissection (ND) is a major surgery for head and neck cancer. Currently, some or all of the spinal accessory nerve (SAN), sternocleidomastoid muscle, and internal jugular vein (IJV) are aggressively preserved during ND to reduce postoperative complications. Since the anatomical relationship between the SAN and IJV has several variations, knowledge of these variations is necessary to avoid iatrogenic damage. In the present case, the SAN was observed to pass through the fenestrated IJV at the level of the posterior belly of the digastric muscle during ND in a patient with squamous cell carcinoma of the mandible. Although the anatomical structure of the SAN and IJV is rare, surgeons must be aware of this anatomical variation.