The aim of this study was to describe the radiographic features of the medial depression of the human mandibular ramus (MDMR) on CT images. The radiographic features of the depression were assessed on multiplanar reformatting (MPR) section of CT scans of eighteen mandibles with 36 MDMRs. The MDMR was observed to be a smooth bone concavity with intact medial and lateral cortical plate located on the medial aspect and anterior to the greatest depth of the sigmoid notch. The average mediolateral depth of the depression was 1.64 mm (Std Dev 0.63 mm), while the average thickness of the thinnest area of the mandibular ramus at the site of the depression was 1.08 mm (Std Dev 0.33 mm). The average anterioposterior width of the depression was 10.39 mm (Std Dev. 3.36 mm). The soft tissue window images showed that the temporalis tendon inserts at the depression in all cases. MDMRs have CT features that help in its identification.
KEY WORDS: Mandible; Abnormalities; Anatomy & histology; Diagnostic imaging.
INTRODUCTION
The medial depression of the human mandibular ramus (MDMR), also called medial sigmoid depression, is a variation of normal anatomy seen on the medial aspect of the ramus of the mandible just below and anterior to the greatest depth of the sigmoid notch. This depression has been described in the literature on anatomical studies on human mandibles and on panoramic radiographs (Langlais et al., 1983; Clark & McAnear, 1984; Langland et al., 1989; Kang, 1991; Carvalho et al., 2001; Dalili & Mohtavipour, 2003; Sudhakar, 2014). On panoramic radiographs, it appears as a radiolucency resembling a foramen (pseudoforamen) and may even be misinterpreted as a pathological condition or pseudocyst (Langlais et al.; Clark & McAnear) (Fig. 1). It was first reported by Langlais et al. in a study on dry human skulls. They described MDMR on panoramic radiographs made of the skulls as a unilateral or bilateral, small, round, ovoid or triangular well-defined radiolucency that generally lacks a cortical margin. Salivary gland-related cortical defects involving the ascending ramus (Stafne bone defect) have been reported (Prapanpoch & Langlais, 1994; Campos et al., 2004; Hisatomi et al., 2019; Lee et al., 2019). Unlike the medial depression of the mandibular ramus (MDMR), these defects were reported to occur at a more posterior and / or inferior location in the medial or lateral aspect of the mandibular ramus
AL-SADHAN, R. CT study of the medial depression of the human mandibular ramus. Int. J. Morphol., 39(6):1570-1574, 2021.
