Primary orbital extraskeletal osteosarcoma.

The authors describe a case of orbital extraskeletal osteosarcoma. A 78-year-old man with a history of rheumatoid arthritis on long-term corticosteroids had a left medial canthal basal cell carcinoma excision followed by adjuvant radiotherapy. Twelve months later, he re-presented with a large rapidly-growing calcified mass involving his left medial canthus and orbit. An incisional biopsy demonstrated an infiltrate of atypical cells exhibiting mitotic activity with a rosette arrangement around partially calcified necrotic tissue. The patient underwent orbital exenteration and a partial maxillectomy. Histopathology demonstrated an extraskeletal osteosarcoma. It is extremely rare for this tumor to occur in the orbit. Immunosuppression and adjuvant radiotherapy were possible predisposing factors in the development of this tumor. Extraskeletal osteosarcoma (ESOS) is a malignant tumour that produces osteoid. It develops in soft tissue without continuity to bone or periosteum. It is rare and comprises fewer than 5% of all osteosarcomas. Extraskeletal osteosarcoma primarily affects patients above 50 years of age and has a poor prognosis. In this report, we describe the clinical, radiologic, and pathologic records of a rare case of primary ESOS of the orbit.