Adult variant of congenital mesoblastic nephroma.

Congenital mesoblastic nephroma is a relatively rare tumor predominantly of childhood. Occurrence in adults is exceedingly rare and, to my knowledge, only two cases have been reported to date. This article pertains to a mesoblastic nephroma in a 41-year-old woman. The tumor was composed mainly of compact fibrocollagenous elements interspersed with areas containing immature tubules and occasionally glomeruloid structures. There was no evidence of capsular or renal invasion or cytological malignant features. It has been postulated that this neoplasm may represent a form of mature Wilms' tumor with a benign clinical course.