(A600) Posterior Belly of the Digastric: Not Always the Resident's Friend?

Introduction: We present a patient who was found to have an anatomic variation of the external carotid artery and its relationship with the posterior belly of the digastric muscle.

Methods: This is the case report of a single patient with a history of oropharyngeal squamous cell carcinoma who was undergoing surgical treatment consisting of oropharyngectomy and neck dissection. Anamolus anatomy was identified at the time of neck dissection.

Results: The standard anatomical landmarks were identified and exposed for neck dissection, including the sternocleidomastoid muscle and the spinal accessory nerve. Dissection continued beneath the submandibular gland, revealing the posterior belly of the digastric muscle (PBD) in its expected position.

However, during further inferior mobilization of the soft tissues overlying the PBD, a significant anatomical variant was encountered. The external carotid artery (ECA) was found traversing superficial to the PBD, deviating from its usual deep course. The tendon of the PBD could be visualized posteriorly. This unexpected finding necessitated a meticulous dissection technique to ensure safe preservation of the aberrant ECA.

Conclusions: Though the occurrence of this anatomic variation is rare, knowledge of its existence may prove critical in preserving the external carotid artery during procedures that require dissection of the posterior belly of the digastric and the stylohyoid.