Retroperitoneal Malignant Fibrous Histiocytoma

We present 2 cases of malignant fibrous histiocytoma (MFH) of the retroperitoneum. Only 12-14% of all MFH occur in the retroperitoneum. Both patients were operated with the diagnosis of a kidney tumor. The surgical exposure showed a tumor arising from the retroperitoneum, infiltrating or surrounding the kidney. We would like to emphasize that large tumors of the retroperitoneum which resemble kidney tumors can also arise from mesen-chymal tissue.