An infant with an abdominal mass

Mesoblastic nephroma, also known as congenital mesoblastic nephroma or fetal renal hamartoma, is a rare renal mesenchymal tumor with low malignant potential, occurring most commonly in infants. A case is presented which could be diagnosed on fine needle aspiration cytology complemented with cell-block immunocytochemistry. The cytopathologists need to be aware of the cytologic and immunocytochemical features of this entity, to accurately diagnose these cases pre-operatively, so as to avoid unnecessary administration of chemotherapy to these infants.