Cystic nephroma.

The clinical and pathologic findings of four cases of cystic nephroma (so-called "renal multilocular cyst") in four infants nephrectomized with the diagnosis of Wilms' tumor are presented. Each lesion consisted of an encapsulated mass composed of cysts separated by thin septa. Histologically the cysts were lined by epithelium, and the septa contained foci of immature metanephric blastema (abundant in one case and sparse in another). rhabdomyocytes and mature tubules. Neither embryonic ducts nor cartilage were seen. One cystic lesion was adjacent to a nephroblastoma which formed a separate nodule. No recurrences of metastases developed, and the only death was due to postoperative sepsis. These lesions are considered by some authors to be dysplasia, while others interpret them as benign neoplasms. Our findings and a review of the literature probably represent the differentiated counterpart of nephroblastoma.