Two chromosomally different cell populations in a partly cellular congenital mesoblastic nephroma.

The conventional fibromatous and cellular areas of a congenital mesoblastic nephroma were studied using electron microscopy, and in vitro and cytogenetic methods. In light- and electron-microscopic studies, as well as in cell cultures, mature and immature mesenchymal cell types that corresponded to the fibromatous and cellular areas of the tumor were found. The conventional fibromatous portion of the tumor showed a normal chromosomal pattern, while the cellular, pleomorphic tumor area was characterized by an aneuploid clone with 54 chromosomes. The value of cytogenetic analysis of congenital mesenchymal renal tumors as a possible diagnostic tool in histologically questionable cases is discussed.