Congenital extrahepatic portosystemic shunt (CEPS), also known as Abernethy malformation, occurs when blood vessels near the liver do not form correctly during fetal development. The hepatic portal vein delivers blood to the liver; in CEPS, the portal vein may not develop or another blood vessel may attach to the portal vein, redirecting (shunting) blood away from the liver rather than through the liver. CEPS is divided into two types based on if blood can flow through the liver. In type 1, certain blood vessels in the liver are missing. In type 2, these blood vessels are present but they have abnormal connections. Both types can be associated with other complications, such congenital heart disease, liver disease, nodules on the liver, and hepatic encephalopathy. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.