The Couinaud classification (pronounced kwee-NO) is used to describe functional liver anatomy. It is preferred over morphological liver anatomy since it allows the division of the liver into 8 independent functional units rather than relying on the traditional morphological description based on the external appearance of the organ.
The separation of the units is based on the fact that each 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 classification system uses the vascular supply in the liver to separate the functional units (numbered I to VIII):
- right hepatic vein divides the right lobe into anterior and posterior segments
- middle hepatic vein divides the liver into right and left lobes (or right and left hemiliver): this plane runs from the inferior vena cava to the gallbladder fossa
- left hepatic vein divides the left lobe into a medial and lateral part
- portal vein divides the liver into upper and lower segments: the left and right portal veins branch superiorly and inferiorly to project into the centre of each segment
The division of the liver into self-contained units means that each segment can be resected without damaging those remaining. For the liver to remain viable, resections must proceed along the vessels that define the peripheries of these segments. This means, that resection-lines parallel the hepatic veins and there is preservation of the centrally located portal veins, bile ducts, and hepatic arteries.
- unit I is the caudate lobe and is situated posteriorly.
- units II and III lie lateral to the falciform ligament with II superior to the portal venous supply and III inferior.
- unit IV lies medial to the falciform ligament and is subdivided into IVa (superior) and IVb (inferior).
Units V to VIII make up the right hemiliver.
- unit V is the most medial and inferior.
- unit VI is located more posteriorly, with
- unit VII above it.
- unit VIII sits above unit V in the superio-medial position.
It was first described by C Couinaud in 1957
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- 1. Thieme Atlas of Anatomy (Neck and Internal organs): ISBN 3131421118 1.
- 2. University of Iowa, College of Medicine: Couinaud classification
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