This photomicrograph is from a congenital mesoblastic nephroma that presented as a 5.1 cm right renal mass in a newborn female at 33 weeks gestation. It is the most common congenital renal neoplasm and comprises about 2% of all pediatric renal tumors. Congenital mesoblastic nephroma, classic type, has a whorled cut surface similar to leiomyomas. The tumor consists of intersecting bundles of fibroblastic cells invading the renal parenchyma.
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