Case 11 - Cystic Nephroma

Slide 21 - Delicate fibrous septa, low magnification Slide 22 - Cysts lined by flattened epithelial cells, high magnification Click on thumbnail images of slide for an enlarged view Gross Features: These lesions are well-circumscribed by a fibrous capsule and are composed of multiple noncommunicating locules with smooth inner surfaces and containing clear yellowish fluid. Solid areas are absent or scanty and the septa range from paper-thin to a few millimeters thick. Microscopic Features: Microscopically, the septa are composed of fibrous tissue which may contain foci of calcification. In some cystic nephromas the septal tissue is cellular and resembles ovarian stroma. The septa may contain differentiated tubules (as opposed to tubules with the morphology characteristic of Wilms' tumor), inflammatory cells, and reactive fibroblasts. The cysts are usually lined by flattened or low cuboidal epithelium with small amounts of cytoplasm; occasionally the lining cells have a hobnail configuration.   Differential Diagnosis: 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. Cystic nephroma is benign and cystic partially differentiated nephroblastoma has little or no potential for metastasis   Cystic Renal Cell Carcinoma Frequency (15% of All Renal Cell Carcinoma) 6% Multilocular 5% Unilocular cystadenocarcinoma 3% Cystic necrosis 1% Arising in pre-existing simple cyst The great majority of cystic nephromas occur in women over 30 years of age. In this population, the most important differential diagnostic consideration is multilocular; cystic renal cell carcinoma. This variant of clear cell renal cell carcinoma contains l microscopic clusters of epithelial cells with clear cytoplasm in some of the septa. Often the population of cells with clear cytoplasm is small so thorough sampling is important. Individually, these cells are identical to grade 1 clear cell renal cell carcinoma. Since histiocytes in the septa may be difficult to distinguish from the clear cells, immunohistochemistry for epithelial membrane antigen or cytokeratins can be useful to confirm the nature of the cells.