A 15-year-old male patient accepted to emergency department with nausea, vomiting, sleepiness, and severe epigastric pain. The patient has a history of mild mental retardation since his childhood. Physical examination showed epigastric tenderness. Laboratory findings were consistent with mildly increased liver enzymes and hyperammonemia. Result of abdominal ultrasound was suboptimal due to lack of patient cooperation. Patient underwent abdominal and thoracic computed tomography (CT) examination to investigate the possible causes of hyperammonemia and liver disease. The CT scan showed the absence of portal vein with direct connection of portomesenteric system with systemic venous circulation. There were also various arterial and venous anomalies along with multiple hepatic masses. Whole anatomy of the thorax and abdomen was delineated with multiplanar reformatted images and maximum intensity projection technique. Imaging findings are consistent with Type Ib Abernethy malformation. The patient also underwent brain magnetic resonance imaging to investigate the presence of central nervous system changes due to hyperammonemia.