Renal tumors in the neonatal period.

Eight infants with renal tumors diagnosed in the first month of life are presented. Three well-differentiated mesenchymal tumors were studied using angiographic and electron-microscopic techniques in addition to conventional histologic methods. The morphology of these unusual tumors is presented in detail and classification as benign fibromyoma or fibromyomatous hamartoma is defended. An association between renal tumors in the newborn and maternal polyhydramnios is also documented for the first time.