A case of epidermoid cyst arising in the masticator muscle space with bone absorption

Epidermoid cysts develop through the inclusion of the ectoderm or epithelial tissue. They mostly occur at the floor of the mouth, but rarely at other loci in the oral region. Here, we report a case of an epidermoid cyst arising in the masticator muscle space. The patient was a 60-year-old man who was referred to our hospital complaining of swelling and pain in the inner part of the right mandibular ramus. Computed tomography and magnetic resonance imaging revealed a monocytic lesion in the right masticatory muscle and pterygomandibular space. Compressive bone resorption was observed on the buccal side of the maxillary right molar alveolar bone and lingual side of the right mandibular ramus cortical bone. The lesion was enucleated under the clinical diagnosis of cyst or benign tumor in the right masticatory muscle space. Histopathological findings showed that the resected specimen has a cyst wall lined with a layer of squamous epithelium with parakeratosis, but without skin appendages. Thus, this was diagnosed as an epidermoid cyst. Recurrences did not occur 41 months after the surgery.