Renal tumors in children under one year of age.

Among 202 primary renal tumors of childhood collected over 33 year period, 22 (10.8%) occurred in children under one year of age. Fifteen were of classic triphasic Wilms' tumor. Three were partially cytodifferentiated variants of Wilms' tumor. The remaining 4 cases were distributed among the mesenchymal renal tumors: congenital mesoblastic nephroma, cellular mesoblastic nephroma, clear cell sarcoma and malignant rhaboid tumor. The morphology of these tumors is presented. Our findings and the review of the literature show the wide morphologic spectrum of these neoplasms and the importance of recognizing them as distinct clinicopathologic entities.