A Rare Case of Intraosseous Mucoepidermoid Carcinoma of the Left Hemi‐Mandible, Masquerading as an Odontogenic Tumour

ABSTRACT Introduction Primary intraosseous mucoepidermoid carcinoma (MEC) of the jaws is a vanishingly rare entity, accounting for 2%–3% of all MEC diagnoses. Albeit its low incidence, intraosseous mucoepidermoid carcinoma is the commonest and most well recognised intraosseous salivary gland neoplasm. These neoplasms typically present in middle‐aged adults, with a slight female predilection. Their incidence within the mandible is three times that of the maxilla, with the posterior body of the mandible and ascending ramus being the most common intraoral sites of involvement. Typically, they come to attention due to cortical expansion. Some lesions are entirely asymptomatic, with only a minority being associated with occasional pain or facial paralysis. Clinical History A 75‐year‐old gentleman presented with an 8‐year history of non‐worsening, intermittent otalgia. CT neck, chest‐abdomen, and pelvis (NCAP) revealed the presence of a locally advanced, expansile, and destructive lesion within the left body and ramus of the mandible. The mandibular left wisdom tooth was extracted, and a biopsy of the lesion was performed. Histology and Laboratory Investigations Histologic examination revealed the presence of a cystic neoplasm comprised primarily of clear cells. Immunohistochemistry was performed and expert opinion sought. The diagnosis was ultimately achieved using molecular studies, which showed the presence of a MAML2 rearrangement, confirming the diagnosis of MEC. Surgical Management Surgical resection was carried out, with the patient undergoing a left hemi‐mandibulectomy and left‐sided supraomohyoid selective neck dissection. The mandibular defect was reconstructed using a mandibular reconstruction plate and right vastus and anterolateral (ALT) free flap. Following this, the patient received adjuvant radiotherapy and is under periodic review with no evidence of disease recurrence to date. Conclusion Intraosseous MEC may clinically, radiographically, and histologically mimic other disease entities more commonly encountered within the jaws given its unusual location and variable histologic presentation, making the diagnosis challenging. Identification of MAML2 rearrangement via molecular studies greatly facilitates the diagnostic process due to its high specificity for MEC. The overall prognosis is favourable with appropriate treatment, highlighting the importance of careful histologic evaluation and use of molecular studies. Trial Registration: Clinical Trial Number: 184/2023