Intrascrotal Wilms' tumor developing in a heterotopic renal anlage of probable mesonephric origin.

A case of intrascrotal primary Wilms' tumor is reported. The histopathologic appearance of the primary tumor and subsequent pulmonary metastasis are identical with that of a typical intrarenal Wilms' tumor. The origin of this tumor in a heterotopic renal anlage consistent with mesonephric origin suggests that tissue from the intermediate and caudal segments of the nephrogenic cord may produce Wilms' tumor. Wilms' tumor arising in an embryologic rest of renal tissue is a rare occurrence. We are reporting the seventh well-documented case and the first case with confirmed distant metastasis.