Couinaud segment

In the widely used Couinaud (or "French") system of anatomy of the liver, the functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein. The system is named after Claude Couinaud.

The fissure for the round ligament of the liver (ligamentum teres) also separates the medial and lateral segments. The medial segment is also called the quadrate lobe. In the widely used Couinaud (or "French") system, the functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein. The caudate lobe is a separate structure which receives blood flow from both the right- and left-sided vascular branches. The Couinaud classification of liver anatomy divides the liver into eight functionally independent segments. Each segment has its own vascular inflow, outflow and biliary drainage. In the centre of each segment there is a branch of the portal vein, hepatic artery and bile duct. In the periphery of each segment there is vascular outflow through the hepatic veins. The division of the liver into independent units means that segments can be resected without damaging the remaining segments. To preserve the viability of the liver following surgery, resections follow the vessels defining the peripheries of each segment. This means that resection lines parallel the hepatic veins, leaving the portal veins, bile ducts, and hepatic arteries intact.

The classification system uses the vascular supply in the liver to separate the functional units (numbered I to VIII):

The remainder of the units (II to VIII) are numbered in a clockwise fashion:

Units V to VIII make up the right part of the liver:

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