Giant retroperitoneal pelvic hemangiopericytoma.

Hemangiopericytoma is a rare soft tissue sarcoma, comprising less than one percent of all vascular neoplasms. This report describes a 75-year-old man with a very large malignant retroperitoneal hemangiopericytoma that was successfully excised. The tumor measured 23 cm in its greatest dimension and, as such, is the largest malignant hemangiopericytoma reported to date. The clinical and pathologic features of this lesion and a review of the literature are presented.