Well-differentiated intraosseous osteosarcoma in the sacrum: a case report.

Hereby we report a case of well-differentiated intraosseous osteosarcoma in the sacrum. A 32-year-old woman was admitted to our hospital with a low echo-level mass in the pelvis searched by ultrasound in a routine physical examination. Radiographically, the mass was misdiagnosed as a benign bony tumor originating from the sacrum. The tumor was completely resected and pathological diagnosis was intraosseous well-differentiated osteosarcoma. Twelve months after operation, the patient was well and there was no evidence of recurrence and distal metastasis. This is a peculiar case of well-differentiated osteosarcoma involving an unusual site of the sacrum. The radiographic appearance and the differential diagnosis are discussed. We consider that dense trabeculated-like bone within an intraosseous solid mass might be suggestive of a well-differentiated osteosarcoma that was valuable in guiding the treatment and prediction of its prognosis. Well-differentiated osteosarcoma, although malignant, may be mistaken for a benign condition. Local excision has almost always been associated with recurrence. For this case, the patient had a wide excision and had no recurrence and metastasis. Therefore, it is very important to identify the radiological features and to distinguish this tumor from benign lesions and high-grade osteosarcomas before operation.