Mesonephroid blastoma. A previously undescribed renal tumor of childhood

We describe a renal tumor arising in a 4 1/2-year-old boy and characterized by the formation of epithelial tubules in a primitive mesenchymal stroma. We call attention to certain unique structural features of this tumor, which set it apart from Wilms' tumor. The tissue components regularly observed in Wilms' tumor were absent from the primary neoplasm despite exhaustive search, suggesting that this case should be considered distinct from nephroblastoma. However, a metastasis appeared that was formed entirely by undifferentiated nephrogenic cells. Based on structural appearance, histogenesis from mesonephros is tentatively proposed. No precedent was found in the literature of a tumor of this description.