An abdominal mass in the neonate or child is most frequently of renal origin. In older infants and children, there is an increase in the incidence of renal neoplasia, while the developmental cystic anomalies more typical of early infancy become less frequent. Wilms tumor is the most common abdominal neoplasm of childhood: there are approximately 7.8 cases per million children each year. Less frequently encountered renal neoplasms include congenital mesoblastic nephroma, multilocular cystic nephroma, clear cell sarcoma, rhabdoid tumor, and renal cell carcinoma. Each of these tumors may mimic Wilms tumor.
The purpose of this issue is to familiarize the radiologist with the less frequently encountered renal neoplasms in childhood and to emphasize that all of these renal neoplasms may mimic Wilms tumor, the most common abdominal neoplasm of childhood.