Cystic mesoblastic nephroma.

Mesoblastic nephroma is the most common solid renal neoplasm in the first few months of life. It has been recognized only recently as a distinct entity, having been classified previously as Wilms tumor. There are relatively few ultrasonic descriptions of this entity in the literature. We present an additional case featuring a large peripheral cystic component with a solid central core demonstrated on ultrasonograhy. This feature is not specific for mesoblastic nephroma and occurs in cystic Wilms tumor.