A liver segment is one of eight segments of the liver as described in the widely used Couinaud classification (named after Claude Couinaud) in the

anatomy Anatomy () is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old scien ...

of the

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

. This system divides the lobes of the liver into eight segments based on a

transverse plane A transverse plane is a plane that is rotated 90° from two other planes. Anatomy The transverse plane is an anatomical plane that is perpendicular to the sagittal plane and the dorsal plane. It is also called the axial plane or horizonta ...

through the bifurcation of the main

portal vein The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Approxima ...

, arranged in a clockwise manner starting from the caudate lobe.

Couinaud segments

There are four lobes of the liver. The Couinaud classification of liver anatomy then further 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 segments (numbered to )

Caudate lobe

Segment is the caudate lobe and is situated posteriorly. It may receive its supply from both the right and the left branches of portal vein. It contains one or more hepatic veins which drain directly into the

inferior vena cava The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...

(IVC). The caudate lobe is a separate structure which receives blood flow from both the right- and left-sided vascular branches. The Caudate lobe includes: (1) the Spiegel lobe; (2) the paracaval portion; and (3) the caudate process portion. The Spiegel lobe has its portal venous and biliary branches ramified mainly from the left-side tract. The Paracaval portion has the portal venous branches ramified mainly from the left portal vein, while the biliary branches of this portion drained into the right and left biliary tracts at almost equal frequencies. The portal venous branches & Biliary branches of the caudate process portion has it ramified from the right-side tract.

Left lobe

Segments and lie medial to the falciform ligament with superior to the portal venous supply and inferior. Segment lies

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

to the falciform ligament and is subdivided into (superior) and (inferior).

Right lobe

Segments to make up the right part of the liver: *Segment is the most medial and inferior *Segment is located more posteriorly *Segment is located above segment *Segment sits above segment in the superior-medial position

Quadrate lobe

The

fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure A ...

for the round ligament of the liver (ligamentum teres) separates the medial and lateral parts of segment . The inferior medial segment () is also called the quadrate lobe.

Society

The clockwise numbering of liver segments in Couinaud's classification is said to have been inspired by the numbering of arrondissements (administrative districts) of Paris.

References

{{Accessory digestive glands Liver anatomy