Solid areas are absent or scanty and the septa range from paper-thin to a few millimeters thick.
In some cystic nephromas the septal tissue is cellular and resembles ovarian stroma. To the naked eye, cystic partially differentiated nephroblastoma, multilocular cystic renal cell carcinoma and cystic nephroma are indistinguishable. Microscopically, cystic parltally differentiated nephroblastoma is distinguished by the presence of blastema or immature Wilms' tumor tubules in its septa. The great majority of cystic nephromas occur in women over 30 years of age. This variant of clear cell renal cell carcinoma contains l microscopic clusters of epithelial cells with clear cytoplasm in some of the septa.