Intramasseteric dermoid cyst: Imaging clues to a rare masticator space lesion

Abstract

Dermoid cysts are benign developmental lesions arising from ectodermal inclusion during embryogenesis. Their occurrence in the head and neck is uncommon, and localization within the masseter muscle is exceptionally rare. We report the case of a 35-year-old woman presenting with painful right cheek swelling and trismus initially misdiagnosed as cellulitis. Contrast-enhanced CT and MRI revealed a well-circumscribed intramasseteric lesion containing intralesional fat and calcifications suggestive of a dermoid cyst, initially raising the differential diagnoses of intramuscular hemangioma and deep facial abscess. Complete surgical excision was performed through an external mandibular approach. Histopathological examination confirmed the diagnosis by demonstrating a cyst lined with keratinizing stratified squamous epithelium with sebaceous glands. The postoperative course was uneventful with no evidence of recurrence at 12-month follow-up. This case highlights the importance of imaging in identifying the characteristic features of a dermoid cyst and in guiding the diagnostic approach to cystic lesions of the masticator space, thereby helping distinguish this rare entity from vascular and infectious mimics.