A Cadaveric Case Report of Bilateral Accessory Anterior Bellies of the Digastric Muscles.

The digastric muscle is a suprahyoid muscle that is composed of an anterior belly and a posterior belly, which originate from the first and second pharyngeal arches, respectively, and they are innervated by the nerves of these arches. The digastric muscles are involved in the elevation of the hyoid bone and depression of the mandible during mastication, speech, and swallowing. In this report, we present the rare case of bilateral accessory anterior belly of the digastric muscles (ABDMs) that originated from the digastric fossa, medial to the anterior bellies. Both accessory anterior bellies crossed the midline and joined the intermediate tendon on the contralateral side. The crossing of the accessory anterior bellies along with the normal anterior bellies resulted in an M-shaped muscular configuration at the submental region. The innervation was identified bilaterally as a branch from the ipsilateral mylohyoid nerve supplying the normal and accessory anterior bellies. It has been hypothesized that abnormal migration of neural crest cells, traditionally responsible for the development of the first pharyngeal arch, results in the formation of an accessory ABDM. Although anomalies of the ABDM are rare, they can present a diagnostic dilemma during radiologic and surgical evaluation. Accessory ABDMs can be used as a muscle or tendon graft in surgical reconstructive procedures; aside from this, they are of limited biomechanical significance.