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 classic variant (shown here) is variably cellular and consists of intersecting fascicles of bland spindle cells with tapered nuclei and eosinophilic cytoplasm. The appearance resembles uterine leiomyomas or infantile fibromatosis.