The human digastric muscle: patterns and variations with clinical and surgical correlations

The digastric muscle is located in the suprahyoid region on each side and frequently exhibits two muscular bellies (anterior and posterior) linked by an intermediate tendon. The paired digastric muscles act together either depressing the mandible or elevating the hyoid bone; therefore acting as a single muscle with important physiological roles. In the present study, the digastric muscle has been analyzed bilaterally in 74 adult human cadavers. A computerized morphometrical investigation of the digastric muscles has been performed (Image Pro Plus software package, Media Cybernetics, USA) and the resulting quantitative data have been statistically assessed (SPSS 11.0 for Windows, USA). We hereby propose an original morphological classification that encompasses five types (I-V) for the anterior belly (AB); three types (I-III) for the intermediate tendon (IT); and two types (I-II) for the posterior belly (PB) of the human digastric muscle. In each digastric muscle, the aforementioned anatomical types have been characterized according to the muscular bellies and intermediate tendon. Consequently, as a result of the combinations of those diverse types, individual digastric muscles have been considered as pertaining to distinctive morphological patterns (named from A to J). Cases with absence of either AB or PB have been included in patterns K and L and would be more appropriately defined as monogastric muscles. This innovative classification provides clear-cut anatomical parameters for interpreting morphological variants of the digastric muscle with relevant clinical and surgical correlations.