Below is an image from Radiopaedia‘s Couinaud classification of hepatic segments. Last revised by Arlene Campos on 5 Jun 2024.
The Couinaud classification (French eponym: pronounced kwee-NO) is the most widely used system to describe functional liver anatomy. It is the preferred anatomy classification system as it divides the liver into eight independent functional units (termed segments) rather than relying on the traditional morphological description based on the external appearance of the liver.
Delineation of segments
The delineation of the segments is based on the fact that each segment has its own dual vascular inflow, biliary drainage and lymphatic drainage. Generally, each segment can be conceptualised as wedge-shaped with the apex pointing towards the hepatic hilum (porta hepatis) where a single segmental branch of the portal vein, hepatic artery and bile duct enter (the portal triad). Along the boundaries of each segment there is venous outflow through the hepatic veins so that a hepatic vein drains two adjacent segments and each segment has multiple draining hepatic veins. These veins run in 3 vertical planes radiating from the intrahepatic IVC that separate 4 sections of the liver (a section is two segments on top of each other):
- right hepatic vein located in the right intersegmental fissure divides the right lobe into right lateral (posterior) and right medial (anterior) sections.
- middle hepatic vein lies in the main lobar fissure, divides the liver into right and left lobes (or right and left hemiliver): this vertical plane runs from the inferior vena cava to the gallbladder fossa and is known as Cantlie’s line. To the right is the right medial section and to the left is the left medial section.
- left hepatic vein located in the left intersegmental fissure, divides the left lobe into left medial and left lateral sections.
A horizontal plane further divides the liver, known as the portal plane where the portal vein bifurcates and becomes horizontal, dividing each section (or sector) of the liver into superior and inferior segments:
- left lateral section: segment 2 above and segment 3 below the portal plane
- left medial section: segment 4a above and segment 4b below the portal plane
- right anterior (or medial) section: segment 8 above and segment 5 below the portal plane
- right posterior (or lateral) section: segment 7 above and segment 6 below the portal plane
Today I review, link to, and embed “Couinaud Classification of Liver Segments On Ultrasound & CT Scan | Liver Anatomy USG Probe Position” From Dr. Sam’s Imaging Library.
All that follows is from the above resource.
Oct 21, 2024
Couinaud Classification of Liver Segments On Ultrasound & CT Scan | Liver Anatomy USG Probe Position
Eight segments are labeled from 1 to 8.
- Each segment has its own portal venous, hepatic arterial, and biliary supply.
- The middle hepatic vein separates the liver into right and left lobes.
- The right hepatic vein divides the right lobe into anterior and posterior segments.
- The left hepatic vein separates the medial and lateral segments of the left lobe.
- The portal vein branches into the right and left portal veins, which then divide further into segmental branches.
Segment 1 (Caudate lobe): Located on the posterior surface of the liver, near the IVC (inferior vena cava). Can be seen in the transverse or coronal views.
Segment 2 (Left lateral superior): Located in the left lateral superior region of the left lobe. Seen in the left upper quadrant on ultrasound.
Segment 3 (Left lateral inferior): Found in the left lateral inferior part of the left lobe. Also visualized in the left upper quadrant, more inferior to segment 2.
Segment 4 (Left medial segment): Divided into 4a (superior) and 4b (inferior). Positioned between the falciform ligament and the middle hepatic vein. Seen adjacent to the gallbladder fossa.
Segment 5 (Right anterior inferior): Located in the right lobe, below the transverse plane of the portal vein. Close to the gallbladder.
Segment 6 (Right posterior inferior): Found in the posterior portion of the right lobe, inferior to segment 7. Near the right kidney in the lower portion of the liver.
Segment 7 (Right posterior superior): Positioned in the posterior superior portion of the right lobe. Extends toward the diaphragm and can be visualized in the upper right quadrant.
Segment 8 (Right anterior superior): Found in the anterior superior part of the right lobe, above the transverse plane of the portal vein. Located near the diaphragm.
