Extrarenal Wilms' tumor: an ultrastructural and immunoelectron microscopic case report.

Wilms' tumor is the most common malignancy of the genitourinary tract in children but the occurrence of extrarenal Wilms' tumor is extremely rare. Extrarenal Wilms' tumor, which by definition excludes a primary tumor in the kidney, has been reported less than fifty times. The ultrastructural appearance of renal Wilms' tumor has been well documented, but the present report is believed to be the first description of the ultrastructural appearance of extrarenal Wilms' tumor. The authors report, for the first time, localization of intermediate filament proteins (vimentin and cytokeratin) and epithelial membrane antigen (EMA) by immunoelectron microscopy in this neoplasm. Demonstration of the coexpression of vimentin and cytokeratin within the same blastemal cell, as well as the identification of desmosomes in a cell with vimentin intermediate filaments, suggests a relationship between stroma, blastema, and epithelia similar to that proposed in renal Wilms' tumor.