Unilateral aberrant anatomy of the hypoglossal nerve

Neck dissection is often performed in patients with oral cancer to both treat and reduce the risk of subsequent neck metastases. Injury to the hypoglossal nerve may result in dysarthria, dysphagia, and profound difficulty with upper airway control. Although surgical landmarks facilitate intra-operative identification of vital structures to be preserved, they should not be an absolute measure, due to anatomical variants. We present a rare case of unilateral aberrant anatomy of the hypoglossal nerve, passing superficial to the internal jugular vein.

A 70-year-old female presented to the emergency department with an indurated and ulcerated floor of mouth lesion, later confirmed to be a squamous cell carcinoma. She was treated with wide local excision, bilateral selective neck dissection of levels I to III, surgical tracheostomy, anterior mandibulectomy and reconstruction with a left composite radial forearm free flap.

A nerve-like structure was identified crossing superficially and perpendicular to the internal jugular vein within the left neck, which was later determined to be an anatomical variant of the hypoglossal nerve. This was carefully dissected and preserved, and the remainder of the surgery completed uneventfully. On the right, the hypoglossal nerve followed its normal anatomical course. The patient made a good recovery and suffered no neurological complications.

Identification, meticulous dissection and preservation of the hypoglossal nerve is essential in lymphadenectomy involving levels I and II. Detailed knowledge of both normal and variant anatomy is fundamental for surgeons, which will allow for identification and protection of important neurovascular structures, thereby minimising surgical morbidity.