Primary osteosarcoma of the kidney with retroperitoneal hemorrhage. Case report and review of the literature.

Primary osteosarcoma of the kidney is a very rare neoplasm with a very poor prognosis and unclear histogenesis. Only 20 cases have been reported in the literature. It has a strong tendency to recur locally and spread to distant sites. We present the clinical case of a 79-year-old man affected by a primary osteosarcoma of the kidney presenting with substantial retroperitoneal tumor hemorrhage. Laparotomy revealed a massive retroperitoneal hematoma due to a bleeding large stony renal mass with multiple bizarre calcifications. The diagnosis of primary renal osteosarcoma was made on the basis of hematoxylin-eosin staining and confirmed by electron microscopy. Hematoma drainage and radical nephrectomy were performed. To our knowledge this is the first case of bleeding renal osteosarcoma reported in the literature. The most important clinical findings, the pathogenesis and the treatment modalities of this rare neoplasm are discussed.