Congenital mesoblastic nephroma: Antenatal and postnatal sonographic appearance with pathologic correlation

Congenital mesoblastic nephroma is the most common neonatal renal tumor. Although the mass may be large and is usually associated with polyhydramnios, these tumors rarely recur and rarely metastasize. Presented is a case, with clinical-pathologic correlation, of a pregnant female with size-greater- than-dates secondary to polyhydramnios associated with a congenital mesoblastic nephroma. This diagnosis should be considered in any fetus with polyhydramnios and a large flank/abdominal mass.