A 6-year-old boy was brought to Milwaukee Children's Hospital by his parents because a large abdominal mass had developed. He had suffered a blow to the abdomen seven weeks earlier in a bicycle accident. Subsequently, he experienced intermittent abdominal pain, anorexia, and low-grade fever. When examined two weeks after the accident, he was normal. Symptoms subsided shortly after this, and he had remained asymptomatic. His mother felt the abdominal mass when she was helping him dress.
On physical examination, a large, nontender, left upper-quadrant mass was palpated. A soft bruit was heard over the mass and over the left femoral artery. Results of laboratory studies were normal except for a mild normocytic anemia, and the serum amylase level was 1,050 Somogyi units. A barium upper gastrointestinal (BUGI) tract fluororoentgenographic examination (Fig 1) was obtained and was followed by a sonographic examination of the abdomen (Fig 2). The boy was prepared