Congenital portosystemic shunts are a rare condition, classified as:

• intrahepatic portosystemic shunt. where communication occurs after the division of portal vein, to hepatic veins or IVC
• extrahepatic portosystemic shunt (CEPS) communication occurs before the division of portal vein between the portomesenteric vasculature, and a systemic vein

CEPS further classified to:

• type 1 (end-to-side shut) where the portal vein is directly communicating with the IVC with absent of intrahepatic portal branches
• type 2 (side-to-side shunt) where intrahepatic are intact, however, blood flow is diverted to systemic veins
• the term Abernethy malformation is an eponym for CEPS, and type 1 shunts are occasionally called the congenital absence of the portal vein