A large calcified retroperitoneal extraskeletal osteosarcoma with consequent bilateral hydronephrosis

Abstract. – Extraskeletal osteosarco ma (ESOS) is a rare malignan t mesenchymal neo- plasm that accounts for less than 4% of all os- teos arcoma s an d approxim ate ly 1-2% of all soft tissue sarcomas. The tumor is typically lo- cated in the deep soft tissues, without attach- men t to skeletal bones. Al tho ugh ESOS has been found to develop virtually in every organ, its most comm on loca tions are the limbs. In the case of abdominal or pelvic lesions the di- agnosis can be very difficult, thus it necessari- ly requi res confirmat ion after explorator y la - parot omy and histo pat ho lo gy. Su ch tum or s may reach enor mous siz es bef ore dete ct ion because the enlarg ing mass may not be asso- ciated with pain. ESOS may be one of the dif- feren tial diagnos es to be conside red in the case of ca lc ified masses ar ising in ret roperi - toneal space. Here we describe a bulky, bilater- al, metastatic ESOS arising from the retrope ri- toneum and causing obstructive uropathy with consequent hydronephrosis.