How Reliable Is the Posterior Belly of the Digastric Muscle in Preventing Carotid Injury During Neck Dissection?

The posterior belly of the digastric muscle, referred to as the "resident's friend," serves as a valuable anatomical landmark because identification of its location during head and neck surgery helps to secure vital structures. A 53-year-old female was referred for an oral cavity mass with a biopsy confirmed squamous cell cancer. A physical exam revealed a 4 cm long and 2 cm wide right ulcerated oral tongue mass. Imaging findings demonstrated no evidence of pathological lymph nodes and distant metastasis. A surgical excision with elective neck dissection was planned along with submental island flap reconstruction. During the neck dissection, the external carotid artery (ECA) was noted to be passing over the posterior belly of the digastric muscle and then descending deeper than the stylohyoid muscle. No other vascular anomaly was identified. The surgery was completed without any complications, and the patient was discharged on post-operative day five. It is necessary to be attentive to a potential course variation of the neurovascular structures underneath that could affect the credibility of the posterior belly of the digastric muscle as a trusted friend. This case report emphasizes the significance of identifying the rare variation where the posterior belly of the digastric muscle exposes the ECA to its lateral side.