A 5½ girl, an identical twin, was admitted with the sudden onset of left upper quadrant abdominal pain of approximately 12 hours' duration. A few days earlier, she had fallen while playing and had struck her abdomen over a large ball. At that time, no importance was given to the incident.
Physical examination revealed an irritable child with a temperature of 38.3 °C, a pulse of 126 beats per minute, and a blood pressure (BP) of 130/100 mm Hg. She had a hard, tender mass in the left upper quadrant of the abdomen that extended 6 cm below the midcostal margin. The liver was not palpable. Results of urinalysis were normal, as were the BUN and serum electrolyte levels. The hematocrit value on admission was 29% and 16 hours later had declined to 21%, accompanied by a reticulocyte response of 32%. She was transfused with 1 unit of packed