The Couinaud’s classification divides the liver into eight segments. These liver segments are functionally independent.
The liver is divided into segments in the horizontal plane by the right and the left main portal veins.
It is also divided into the vertical plane by the right, middle and the left hepatic veins.
- The middle hepatic vein divides the liver into right and left lobes. This is the main plane called the Cantlie’s line that passes from the inferior vena cava to the gall bladder fossa. This line lies 4cm to the left of the falciform ligament.
- The right hepatic vein divides the right lobe into anterior and posterior segments.
- The left hepatic vein divides the left lobe into medial and lateral segments.
The liver segments are numbered in a clockwise direction starting at the caudate lobe. This is called the Couinaud system.
The liver segments can be numbered counterclockwise starting from the IVC.
The caudate lobe is considered a separate segment. The left lobe has four segments and the right lobe also has four segments.
- The caudate lobe is the segment I.
- The left lateral superior segment is II.
- The left lateral inferior segment is III.
- The left medial superior segment is IV a.
- The left medial inferior segment is IV b.
- The right anterior superior segment is VIII.
- The right anterior inferior segment is V.
- The right posterior superior segment is VII.
- The right posterior inferior segment is VI.
|Goldsmith & Woodburne||Couinaud & Bismuth|
|Caudate Lobe||Caudate lobe||1|
|Left Lobe||Left lateral segment||Left lateral superior segment||2|
|Left lateral inferior segment||3|
|Left medial segment||Left medial superior segment||4a|
|Left medial inferior segment||4b|
|Right Lobe||Right anterior segment||Right anterior inferior segment||5|
|Right anterior superior segment||8|
|Right posterior segment||Right posterior inferior segment||6|
|Right posterior superior segment||7|
Each of these liver segments has its own blood supply, venous drainage, and the biliary drainage.
In the center of each segment, the is a portal triad comprising of a portal vein, hepatic artery, and a bile duct.
At the periphery of each liver segment, there is venous drainage through the hepatic veins. The hepatic veins are intersegmental.
The older anatomy divides the liver into larger right and the smaller left lobe. These lobes are divided by the attachment of the falciform ligament on the anterior surface of the liver. On the visceral surface, this division is demarcated by the grooves for the ligamentum teres and ligamentum venosum.
The liver is further divided into two more lobes namely the caudate lobe and the quadrate lobe.
The caudate lobe lies posteriorly between the IVC and the fissure for the ligamentum venosum.
The quadrate lobe lies anteroinferiorly between the gallbladder fossa and the fissure for the ligamentum teres.