Multilocular cyst of the kidney (cystic nephroma) and cystic, partially differentiated nephroblastoma. Terminology and criteria for diagnosis.

The entities commonly known as multi-locular cyst of the kidney (MLC) and cystic partially differentiated nephroblastoma (CPDN) were reviewed, based on material in the National Wilms' Tumor Study Pathology Center. The authors recommend several modifications of existing terminology and definitional criteria for these lesions. Because MLC probably represents a neoplastic lesion, the designation "cystic nephroma" (CN) is preferred. This term should be used only for predominantly cystic tumors composed entirely of differentiated tissues, without blastema or other embryonal elements. The designation CPDN should be applied to predominantly cystic lesions, lacking nodular solid regions, in which blastemal or other embryonal cells are present in the septa of the cysts. Solid Wilms' tumor with multifocal cystic change should be distinguished from CPDN. Five cases of CN and 18 cases of CPDN were reviewed. No CN, for which follow-up data was available, showed aggressive behavior. Only one case of CPDN underwent local recurrence, and there were no metastases. In general, nephrectomy alone appears to be adequate therapy for CPDN, but regular monitoring by noninvasive techniques would seem advisable.