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.