A 2½-YEAR-OLD boy was referred to the surgery service for excision of a large abdominal mass. The patient had experienced 2 months of abdominal pain and a sudden 60 g/L drop in blood hemoglobin concentration, noted 2 weeks before his hospital admission. Four days before the admission, a 2-cm mass was noted on the right side of the abdomen. On the same day, microscopic hematuria was noted. The initial computed tomography scan of the abdomen revealed an 8× 10-cm mass involving the right kidney (Figure 1). An ultrasonographic examination of the abdomen revealed extension of the mass into the right renal vein and the inferior vena cava.
Four days after the initial signs were noted, the boy underwent surgery. The laparotomy revealed a large lobulated tumor involving the right kidney (Figure 2). The superior aspect of the mass had grown through the capsule of the kidney and was adherent to