Nephrogenic rest associated with a mesoblastic nephroma--what does it tell us?

A 3-year-old girl presented with a tumor in the right kidney that was found to be a mesoblastic nephroma on histological examination. In addition, between the tumor and renal parenchyma there was a large perilobar sclerosing nephrogenic rest--a finding that has rarely been reported previously in non-Wilms renal tumors of childhood. We believe this supports the theory that both mesoblastic nephroma and Wilms tumor arise from the developing kidney but the key difference is the time point at which induction of neoplasm occurs.