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. This image shows extramedullary hematopoiesis in a mesoblastic nephroma, classic type. Islands of erythroid and myeloid precursors and developing renal tubules are surrounded by fascicles of bland spindle cells.