Congenital mesoblastic nephroma (CMN), light micrograph. CMN is a mesenchymal neoplasm of the kidney that usually presents by the age of 6 months. It is the most common congenital renal neoplasm. Three histologic variants have been described - classic (25%), cellular (65%), and mixed (10%). It has excellent prognosis with 95% survival rate following complete resection. The image from a mesoblastic nephroma, classic variant, shows intersecting fascicles of bland spindle cells infiltrating into the renal parenchyma and entrapping islands of developing renal tubules and glomeruli.