Anatomic Variation of the Anterior Belly of Digastric Muscle and Positional Relationship between the Posterior Belly of Digastric and Stylohyoid Muscle

Kim, Da Hye; Do, Hyung Joo; Kim, Hyun Joo; Won, Sung Yoon; Choi, Da Yae; Hu, Kyung Seok; Choi, Jong Hoon; Kim, Hee Jin

Abstract

The digastric muscle is located in the suprahyoid region which consists of anterior belly, intermediate tendon and posterior belly. This muscle is an important landmark when performing an operation of submental and upper neck region. Previous researches have reported about variations of the anterior and posterior belly of digastric muscle. However, there are few studies about the general morphology of the digastric muscle and the relationship with surrounding muscles. The purpose of this study was to analyze the morphology of the anterior belly of digastric muscle and confirm the topographic relationship between the digastric muscle and the stylohyoid muscle of Korean. Thirty-four cadavers (21 males, 13 females; mean age 65 years; range 24~89 years) were used in this study. The skin, subcutaneous tissues, superficial fascia and platysma were removed and a detailed dissection was performed, with extreme care being taken not to damage underlying the muscles of submental and upper neck region. After the dissections, all specimens were sketched and photographed. In 8 specimens, we observed the accessory bellies of the anterior belly of digastric muscle. We classified the accessory bellies into the crossover type (five specimens, 14.7%) that cross the mandibular raphe and unilateral type (three specimens, 8.82%). The findings resulting from observation of the anatomical relationship between the posterior belly of digastric and stylohyoid muscles, the posterior belly of digastric muscle perforated the stylohyoid muscle in 32 cases (65%) out of 49 sides. This case was subdivided into the belly of the stylohyoid muscle lean to the lateral (twenty-one specimens, 42.9%) or medial side (eleven specimens, 22.4%) of the posterior belly of digastric muscle. In 17 specimens (35%), the stylohyoid muscle existed on the medial side of the posterior belly of digastric muscle.