Incidental Finding of Double Posterior Belly of Digastric Muscle in Head and Neck Cancer Patient

The digastric muscles have important roles in swallowing, chewing, speech, and landmark identification during neck dissection. The posterior belly of the digastric muscle (PBDM) is often useful for defining boundaries in surgical neck dissection as it contributes to the carotid, submandibular, and submental triangles. The cadaveric prevalence rate of anatomic variations in the digastrics has been reported to be 31.4% of the population with most occurring in relation to the anterior belly of the digastric muscle (ABDM). Few reports describe variations in the PBDM. While anatomic variants of the digastric muscles do not present with clinical manifestations, they can be mistaken as neck masses and contribute to intraoperative complications.

We present a case report of a 73-year-old male with a past medical history significant for Parkinson's Disease, who was incidentally found to have a duplicate PBDM intraoperatively while receiving surgical management of a left buccal squamous cell cancer.

Nine months prior to surgery, the patient began experiencing trismus and some mild dysphagia that were eventually worked up to reveal left buccal squamous cell carcinoma (SCC). Prior to this, the patient did not have clinical symptoms demonstrating dysfunction that could be related to or indicative of this anatomical abnormality preceding symptoms related to left buccal SCC growth. The procedure included a wide local excision, left modified radical neck dissection and left submental artery island flap with suprahyoid neck dissection. The superior duplicate PBDM was found to be overlying the stylohyoid muscle.

It is important for surgeons operating in the head and neck to be aware of the possibility of this rare variation, and to be conscientious when it is identified so that it does not prohibit or limit a thorough dissection of the neck structures where oncologic clearance is paramount.