Low-grade osteosarcoma of the mandible.

Osteosarcoma (OS), a rare malignant bone tumour arising from primitive bone forming mesenchyme, most often arises in the metaphyses of long bones of the extremities. Bone or osteoid formation within the tumour is characteristic of an osteosarcoma. Craniofacial osteosarcoma (CFOS), most often located in the mandible or maxilla, accounts for only 5-13% of all osteosarcomas. In general, OS of the jaw is a high-grade lesion. Low-grade lesions are rare and represent less than 2% of all osteosarcomas reported in the literature. Because of its rarity and well differentiation, Low-grade OS is usually misdiagnosed as a benign lesion. The clinical and radiographic presentation does not correlate well with the subtle histology picture of a low-grade osteosarcoma which makes the diagnosis difficult.