A 6-day-old, known to have transposition of the great vessels, received care in the neonatal intensive care unit at a tertiary care center. A computed tomography scan was performed for abdominal distention and upper gastrointestinal bleeding, which revealed a "mass lesion" in the left liver lobe. Analysis of antecedent events and the clinical and laboratory course uncovered an iatrogenic etiology and pathogenesis of the lesion. As the nature of the lesion was clarified, no specific therapy was required. This case is presented to show a serious yet preventable complication of a commonly performed procedure.
Keywords: liver mass; portal vein thrombosis; umbilical venous catheter.