Wilms' tumor: its morphology in patients under one year of age.

Of 24 patients aged 1 year or younger, and having conditions diagnosed as Wilms' tumor, only 11 had typical, solid neoplasms with the triphasic histologic composition of blastema cells, epithelial cells, and stromal derivatives. Two of these were bilateral. The remaining 13 cases were distributed among different morphologic categories for which special status has been claimed in recent reports. Chief among these is the rhabdomyomatous form of Wilms' tumor, which accounted for six cases in the present series, three of them bilateral. Two additional cases corresponded to cystic, partly differentiated nephroblastoma (cystic nephroma), and two others to renal sarcomas whose precise relationship with Wilms' tumor is currently a matter of conjecture. No case of typical Wilms' tumor was seen in patients under 6 months of age, but a congenital origin seems certain for the two sarcomas of this series. The cystic form of nephroblastoma accounted for the only other case involving a patient 3 months old or younger.