Objectives: The digastric muscle is an important landmark in head and neck surgeries. Important neurovascular structures such as the spinal accessory and hypoglossal nerves (HNs), internal jugular vein (IJV) and internal carotid artery lie deep to the posterior belly of digastric (PBD); the study relating to it deserves special mention in anatomical literature. Therefore, the present study aims to describe the PBD in relation to the essential anatomical landmarks.
Materials and Methods: This study was carried out using 10 cadavers preserved in 10% formalin. The midpoint of IJV in the neck was identified as the point between the angle of the mandible and midclavicular point. The anatomical landmarks considered for measuring the parameters were tip of the mastoid process (TMP), loop of HN, midpoint of IJV, bifurcation of common carotid artery (CCA) and the midpoint of PBD. Various parameters were measured using the digital calipers.
Results: The length of PBD was 3.77 ± 1.08 cm on right and 3.15 ± 0.05 cm on left side indicating slightly longer belly on the right. The extended length did not vary much on both the sides, which were 6.7 ± 1.23 cm on right and 6.7 ± 0.75 cm. The HN crossed PBD 2.72 ± 0.8 cm anterior to the TMP on right side, while on left side it was situated 2.1 ± 0.57 cm anterior to TMP. The distance between the midpoint of PBD and of IJV was 6.58 ± 0.99 cm on right side, whereas it was 6.1 ± 0.96 cm on left side. The distance between the midpoint PBD and bifurcation of CCA was 3.04 ± 0.61 cm on right and 2.78 ± 0.74 cm on left side.
Conclusion: As the PBD muscle is an important surgical landmark, the present study adds to the existing knowledge about it. The present study has also included few newer landmarks, which were not given importance in the previous studies.
Key words: Carotid arteries, hypoglossal nerve, internal jugular vein, posterior belly of digastric muscle