Bilateral bipartite origin of the posterior belly of digastric muscle: a clinico-anatomical appraisal

Abstract

Anomalous digastric muscle may be an incidental finding during routine dissections or autopsies which may be asymptomatic or symptomatic. While performing routine educational dissection of the submandibular region of the neck, we encountered a unique bilateral composition of the digastric muscle. The posterior belly of digastric displayed a bifid origin. Two muscle bellies emanating from the digastric notch of the mastoid part of temporal bone were found to unite to form a common belly which later joined the intermediate tendon through which it was connected to the anterior belly. The innervation of this accessory muscle also displayed interesting variation. Although on the right side the innervation was solely derived from the facial nerve as is the usual case, an additional twig from the nerve to splenius capitis supplied the accessory belly on the left side. Acquaintance with the variations of this important muscle of the submandibular region is extremely important for radiologists while interpretation of MRI and CT scans and for surgeons performing reconstructive procedures. Additionally, in view of vital neurovascular structures related to the posterior belly of digastric, lack of caution on the part of surgeon may result in severe complications. The present study was designed to elucidate a rare but an important variation of the digastric muscle thereby apprising the head and neck surgeons in their operative endeavors of this region.