Primary extrarenal Wilms' tumor in children.

We report three additional cases of primary extrarenal Wilms' tumor and review those cases previously documented. Analysis of the location, histopathology, treatment, and survival of these cases supports the following conclusions: Wilms' tumor may occur in an extrarenal location without primary renal involvement and must be included in the differential diagnosis of abdominal, pelvic, and inguinal masses; an extrarenal location supports a more frequent occurrence of ectopic metanephric blastema than was previously recognized or origin of Wilms' tumor from a more primitive mesodermal tissue; and the natural history and prognosis of extrarenal and renal Wilms' tumors appears similar.