Masseteric Space Infection Following Mandibular Third Molar Extraction, with an Incidental Finding of Fibrous Dysplasia of the Coronoid Process: A Case Report

Masseteric space infections are uncommon deep facial space infections and are most often of odontogenic origin, particularly following extraction of a mandibular third molar. Owing to the deep anatomical location of the masseteric space, such infections commonly present with trismus, facial swelling, pain, and tenderness, and frequently mimic temporomandibular joint disorders or parotid gland infections. This resemblance may delay diagnosis and appropriate management, thereby increasing the risk of local and systemic complications. The present case report describes a 21-year-old male patient who presented with right-sided facial swelling, pain, restricted mouth opening, and extraoral purulent discharge one month after extraction of the right mandibular third molar. Clinical examination was suggestive of a deep facial space infection. Ultrasonography and Contrast-Enhanced Computed Tomography (CECT) revealed multiple loculated fluid collections within the right masseteric space, together with periosteal reaction and cortical erosion involving the ramus and coronoid process of the mandible. Routine haematological investigations demonstrated leucocytosis, consistent with active infection. The patient was managed by incision and drainage under general anaesthesia, and a significant amount of purulent material was collected intraoperatively from the involved space. Because the CECT findings of cortical erosion and periosteal reaction raised a strong suspicion of associated secondary osteomyelitis of the coronoid process, an appearance that is not pathognomonic and may be mimicked by fibro-osseous and neoplastic lesions, an incisional biopsy of the suspicious osseous tissue was performed concurrently for histopathological confirmation. Histopathological examination unexpectedly revealed features consistent with fibrous dysplasia involving the coronoid process, which may have contributed to the atypically aggressive progression of the infection. The present case highlights the diagnostic challenges associated with masseteric space infections and emphasises the value of advanced imaging in assessing the extent of infection and the associated bony involvement. Early diagnosis, prompt surgical drainage, and appropriate antimicrobial therapy remain essential to prevent serious complications, particularly in the presence of an underlying bone pathology