Mesonephric adenosarcoma of the renal pelvis with heterologous elements

A polypoid tumor located in the renal pelvis with both epithelial and sarcomatous elements is described. The epithelial component was histologically benign and resembled urothelium. The sarcomatous component showed undifferentiated cells and rhabdomyoblastic elements. The term mesonephric adenosarcoma is proposed to describe this biphasic tumor. Although this tumor might be histogenetically related to Wilms' tumor, it is morphologically distinct, and might behave more aggressively.