A 1-day-old boy with a liver mass.

This 1-day-old baby boy was transferred for evaluation of a liver mass. He was the 2,250-g product of a 38-week gestation to a 25-year-old gravida 1 para 1 (G1P1) woman. Following an uneventful pregnancy, labor and delivery, the baby’s abdomen was distended at 25 hours of life. X-rays at the outside hospital revealed an enlarged heart and liver. Ultrasound demonstrated a possible arteriovenous malformation (AVM) prompting transfer. The family history was unremarkable. On exam, the baby was intubated and on the ventilator. Weight and length were below the 5th percentile for age, and head circumference was in the 20th percentile. He was normocephalic. There were no dysmorphic features. There were several 1-2 mm tan nodules noted on both irides. There were two natal teeth. Lungs were clear. S1 and S2 were normal. There was a II/VI holosystolic murmur heard best at the left upper sternal border with radiation to the back. The abdomen was distended. The liver was palpable down to the level of the umbilicus and across the midline beneath the left subcostal margin. There was no