Pathology Case of the Month

Cystic Nephroma (Benign Multilocular Cyst)

Cystic nephroma is an uncommon lesion that occurs in both adults and children with a male predominance in children and a female predominance in adults. The clinical and pathologic differential diagnosis includes cystic renal cell carcinoma and cystic variants of nephroblastoma (Wilms' tumor).

Macroscopic Appearance

Macroscopically, cystic nephroma has a well-circumscribed appearance bounded by a fibrous capsule. The cysts have smooth inner linings and delicately thin walls. No solid areas are present.

Microscopic Appearance

Microscopically, cystic nephroma is characterized by having fibrous septa with benign spindle cells resembling ovarian stroma. The cysts are lined by flattened, low columnar cells occasionally having a hobnail (protruding nuclei) appearance. Collections of cells with abundant clear cytoplasm should steer the diagnosis toward renal cell carcinoma, while solid areas of undifferentiated cells should raise the issue of nephroblastoma.

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