History: A 3-month-old previously healthy girl presented to an outside institution with a 4-day history of low-grade fever, irritability, and a tender "knot" in the upper abdomen. Ultrasonography (US) was performed at an outside hospital. US images were not available for review; however, they showed a mass in the left hepatic lobe, per the outside report, and the patient was referred to our institution for further evaluation. Her parents reported a normal fullterm pregnancy, with regular prenatal care and normal prenatal US findings. The baby was born after an uncomplicated gestation. She was delivered at term via an uncomplicated cesarean section due to a maternal history of cesarean section. The perinatal course was uncomplicated, and there was no history of umbilical catheterization, per the parents. On arrival at our institution, the patient had a temperature of 38.2°C. All other vital signs were normal. Palpation revealed a tender and firm mass in the periumbilical region; otherwise, physical examination findings were normal. Results of laboratory work-up were normal, except for elevated white blood cell count (26 600/mm3 [26.6 × 109/L]; normal, 6000-17 500/mm3 [6-17.5 × 109/L]). The patient underwent US followed by intravenous contrast material-enhanced (10 mL ioversol, Optiray 320; Medtronic, Santa Rosa, Calif) computed tomography (CT) on the same day.