Ossifying tumor of infantile kidney: report of two cases.

Two patients, both male infants, presented with hematuria and were found to have small calcified intrarenal masses interpreted as calculi radiographically. These were found at surgery to be firmly adherent to parenchyma. Dense, stone-like cores, after decalcification, were found to be composed of bone, while the periphery was composed of uniform, undifferentiated cells. We believe these tumors were derived from urothelium rather than the metanephros, and that they represent yet another benign variant of pediatric renal tumors.