Cellular congenital mesoblastic nephroma in a newborn.

Typical nephroblastoma (Wilms'tumor) is uncommon within the first 6 months of life. Renal tumors most commonly found in this age constitute of two groups which have a better and worse prognosis, respectively, than typical nephroblastomas. The group of tumors with a better prognosis encompasses congenital mesoblastic nephroma (CMN), fetal rhabdomyomatous nephroblastoma and cystic, partially differentiated nephroblastoma. The group of tumors with a worse prognosis consists of rhabdoid tumor of the kidney and bone metastasizing renal tumor (clear cell sarcoma) of childhood. Adequate therapy for these two neoplasms has as yet to be developed. Among the low-grade malignant tumors congenital mesoblastic nephroma can be successfully treated with simple nephrectomy. There, are however, variants of CMN which may differ in clinical behavior from the typical form of CMN. These variants include the cellular CMN2 and, possibly, the malignant mesenchymal nephroma of infancy. A case of cellular congenital mesoblastic nephroma is presented here. Its clinical and pathologic features are discussed.