Mesenchymal chondrosarcoma of the left coronoid process: report of a unique case with clinical, histopathologic, and immunohistochemical findings, and a review of the literature.

Mesenchymal chondrosarcoma (MCS) is a rare malignant neoplasm of bone or soft tissue origin, locally aggressive, rare in the oral cavity, of which fewer than 100 cases have been reported in the English literature. This is the first case described of this type of tumor affecting the coronoid process. The report describes a unique case of MCS in a 64-year-old woman who presented with swelling and pain at the left preauricular area just anterior to the left tragus. An orthopantomograph showed a large mass in the temporomandibular joint involving the left coronoid process and extending to the left ramus of the mandible. Biopsy and histopathologic examination revealed a biphasic pattern, composed of an undifferentiated small round-cell component surrounding a myxoid of malignant cartilage; a focally pericytic vascular pattern resembling hemangiopericytoma was observed. Immunohistochemical studies were positive for CD99, S-100, and CD45 and negative for desmin, actin, chromogranin, epithelial membrane antigen (EMA), and cytokeratin. The tumor was treated by extensive hemimandibulectomy followed by reconstruction of the area. There was no evidence of disease at the 8-year follow-up. Previously reported cases are reviewed as well.