Segments of the liver

At a glance

English

Segments of the liver

Latin (TA2)

Segmenta hepatis

System

Digestive

Region

Abdomen

In order

From the posterior segment of liver (i) to the posterior medial segment of liver (viii)

About the segments of the liver

On its surface the liver looks like a large right and a small left lobe divided by the falciform ligament, with the small quadrate and caudate lobes on its underside. These surface lobes do not match how the organ is supplied. Functionally, the liver is divided by the branching of the portal vein, hepatic artery and bile ducts, which run together as portal triads into the organ, while the hepatic veins run between the territories and drain them to the inferior vena cava. On this basis the liver is split into eight segments, numbered I to VIII in a clockwise order when the organ is viewed from the front, in the scheme of Couinaud.

The first division is into a right and a left functional half, or liver, by a plane running from the gallbladder bed to the inferior vena cava, the line of the middle hepatic vein; it lies well to the right of the falciform ligament. The right half is split by the plane of the right hepatic vein into lateral and medial divisions, and the left half by the line of the falciform ligament and umbilical fissure into medial and lateral divisions. Finally, a transverse plane at the level of the main portal branches separates upper from lower segments on the right, while the left lateral division is split into II and III. Segment I, the caudate lobe, stands apart from this pattern.

Members of the series share a common plan. Each has its own portal and arterial inflow and its own biliary drainage at its centre, with hepatic veins at its edges. This means a segment can be removed with little blood loss by tying its pedicle and cutting along the venous planes, and it underlies modern liver resection and the splitting of a donor liver for two recipients.

Surgeons and radiologists use the numbers to describe the exact position of tumours, cysts, abscesses or injuries, and to plan which segments can safely be taken while leaving enough functioning liver. The caudate lobe is often spared in conditions that block the main hepatic veins, because its own small veins open straight into the inferior vena cava, so it may enlarge as the rest of the liver shrinks.

Each segment also drains its bile through its own segmental duct, which joins the others to form the right and left hepatic ducts. Variations in the branching of the ducts and arteries are frequent, so the segment pattern is checked by imaging before any planned resection.