Congenital portosystemic shunts can be divided into two types: intrahepatic shunts in which there is an abnormal connection between the branches of the portal vein and either the inferior vena cava or the hepatic veins and less commonly the extrahepatic type in which the portal system is connected to one of the branches of the mesenteric veins. Here we describe a 73-year-old woman who was admitted to the hospital with clinical evidence of encephalopathy and was found to have hyperammonemia. Abdominal computed tomography angiography was performed and revealed a dilated portal vein measuring up to 1.8 cm at the porta-hepatis along with dilated superior mesenteric and splenic veins. Multiple dilated vascular channels were identified within the right hepatic lobe. An intrahepatic portosystemic shunt between an enlarged middle hepatic vein and two separate branches of the right portal vein was demonstrated. A liver biopsy showed normal architecture with no evidence of inflammation or fibrosis. Portosystemic shunts are rare and often detected in adulthood but should be considered as an important cause of unexplained encephalopathy in the absence of cirrhotic liver disease or hepatic trauma. Given that the size of such shunts increases with age, older persons are more prone to the effect of toxic metabolites.This age-associated increase in shunt size may help explain why some patients remain asymptomatic until later in their life which may account for the late presentation in our patient.