Wilms tumor is responsible for 5% of pediatric malignant tumors or approximately 500 new cases each year in the United States, with equivalent frequency in boys and girls. The incidence is fairly uniform throughout the world, being somewhat more common in black children and less common in Asian compared with white children. The mean age at presentation is 3 years for sporadic and 2 years for hereditary cases.

Children who have Wilms tumor often present with an asymptomatic abdominal mass, found by caregivers or pediatricians. The differential diagnosis for a toddler who has an abdominal mass includes neuroblastoma, hepatoblastoma, sarcoma, lymphoma, and germ cell tumors, as well as benign conditions. At times, patients newly diagnosed as having Wilms tumor experience abdominal pain and hematuria from invasion of the renal pelvis or hypertension from compression of the renal artery, each consequence occurring in approximately 25% of cases.

The most common sites...

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