Juxtaposed cystic nephroma and Wilms' tumor

We report a case of juxtaposed Wilms' tumor (WT) and cystic nephroma (CN) in a 21-month-old girl which gave rise to radiological diagnostic difficulty. Preoperative chemotherapy was given, resulting in marked tumor necrosis but the cystic nephroma remained untouched. Histological examination showed characteristic features of a triphasic WT and a CN; the two lesions were separated by a thick fibrous capsule. While everybody agrees that WT and cystic partially differentiated nephroblastoma (CPDN) are closely related, there are two opposite views about their relationship to CN. One is that CN may represent the final step in maturation of WT and CPDN. Other authors argue that there is no evidence to support this theory but believe CN might have something in common with nephrogenic rests. We suggest that the two lesions in the present case may have originated from two intralobar nephrogenic rests, which would strengthen the latter view.