Extrahepatic CPSS are connections between portal veins and systemic veins that can happen between the main portal vein and the IVC or upstream the portal vein from any vein afferent to the main portal vein and draining in any vein afferent to the IVC, the IVC itself of the heart itself.

Because the blood flow drains mainly through the CPSS, this malformation can cause the complete disappearance of the main portal vein and intrahepatic portal veins and is historically called Abernethy 1 malformation or congenital absence of portal vein.

This connection can cause hypoplasia of the main portal vein and its branches, historically called Abernethy 2 malformation.