In the periphery of each segment there is vascular outflow through the hepaticveins.
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 andleft hemiliver). This plane runs from the inferior vena cava to the gallbladderfossa.
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 projectinto the center of each segment.
Because of this division into self-contained units, each segment can beresected without damaging those remaining. For the liver to remain viable,resections must proceed along the vessels that define the peripheries of thesesegments. This means, that resection-lines parallel the hepatic veins,
The centrally located portal veins, bile ducts, and hepatic arteries arepreserved.
根据Couinaud分段
Segments numbering
There are eight liver segments.
Segment 4 is sometimes divided into segment 4a and 4b according to Bismuth.
The numbering of the segments is in a clockwise manner (figure).
Segment 1 (caudate lobe) is located posteriorly. It is not visible on a frontalview.
顺时钟数字标记段
The illustrations above are schematic presentations of the liversegments.
In reality however the proportions are different.
On a normal frontal view the segments 6 and 7 are not visible because they arelocated more posteriorly.
The right border of the liver is formed by segment 5 and 8.
Although segment 4 is part of the left hemiliver, it is situated more to theright.
Couinaud divided the liver into a functional left and right liver (in French'gauche et droite foie') by a main portal scissurae containing the middlehepatic vein. This is known as Cantlie's line.
Cantlie's line runs from the middle of the gallbladder fossa anteriorly to theinferior vena cava posteriorly.
On this illustration it looks as if the medial part of the left lobe isseparated from the lateral part by the falciform ligament. However it actuallyis the left hepatic vein, that separates the medial part (segment 4) from thelateral part (segments 2 and 3).
The left hepatic vein is located slightly to the left of the falciformligament.
从前方看，看不到六，七段
Transverse anatomy
The far left figure is a transverse image through the superior liver segments,that are divided by the hepatic veins.
The right figure shows a transverse image at the level of the left portal vein.
At this level the left portal vein divides the left lobe of the liver into thesuperior segments (2 and 4A) and the inferior segments (3 and 4
.The left portal vein is at a higher level than the right portal vein.
左：在左门静脉以上水平
右：在左门静脉水平
The image on the far left is at the level of the right portal vein. At thislevel the right portal vein divides the right lobe of the liver into superiorsegments (7 and 8) and the inferior segments (5 and 6).
The level of the right portal vein is inferior to the level of the left portalvein.
At the level of the splenic vein, which is below the level of the right portalvein, only the inferior segments are seen (right image).
左：在右门静脉水平
右：在脾静脉水平
Caudate lobe
The caudate lobe or segment 1 is located posteriorly.
The caudate lobe is anatomically different from other lobes in that it oftenhas direct connections to the IVC through hepatic veins, that are separate fromthe main hepatic veins.
The caudate lobe may be supplied by both right and left branches of the portalvein.
On the left a patient with cirrhosis with extreme atrophy of the right lobe,normal volume of the left lobe and hypertrophy of the caudate lobe.
Due to a different blood supply the caudate lobe is spared from the diseaseprocess and hypertrophied to compensate for the loss of normal liverparenchyma
肝硬化尾叶增大
注意：右叶缩小
Other Classifications and Variants
There are many other anatomical and functional descriptions of the liveranatomy.
In the classical description the external appearance of the liver is used todescribe the anatomy.
However there are many differences between this classical model and thefuctional models, as popularized by Couinaud and Bismuth.
A more detailed discussion of the various models is given in reference 4.
Classical Anatomy
The classical description of the liver anatomy is based on the externalappearance.
On the diaphragmatic surface, the ligamentum falciforme divides the liver intothe right and left anatomic lobes, which are very different from the functionalright and left lobes (or right and left hemiliver).
In this classical description, the quadrate lobe belongs to the right lobe ofthe liver, but functionally it is part of left lobe.
Bismuth's classification
This classification is very similar to the Couinaud classification, althoughthere are small differences. It is popular in the United States, whileCouinaud's classification is more popular in Asia and Europe.
According to Bismuth three hepatic veins divide the liver into four sectors,further divided into segments.
These sectors are termed portal sectors as each is supplied by a portal pediclein the centre.
The separation line between sectors contain a hepatic vein.
The hepatic veins and portal pedicels are intertwined, as are the fingers oftwo hands.
The left portal scissura divides the left liver into two sectors: anterior andposterior.
Left anterior sector consists of two segments: segment IV, which is thequadrate lobe and segment III, which is anterior part of anatomical left lobe.
These two segments are separated by the left hepatic fissure or umbilicalfissure.
Left posterior sector consists of only one segment II. It is the posterior partof left lobe.
Variations
In the Couinaud classification little attention is given to the high prevalenceof anatomical variations which occur, especially in the right hemiliver.
Using volumetric acquisition techniques, such as magnetic resonance imaging orspiral computed tomography scanning, detailed insight into the individualsegmental anatomy can now be obtained in a non-invasive manner (2,3).
The significance of this anatomical insight lies in the planning of anatomicalresections, whereby the relationship between tumour and individual segmentalanatomy can be depicted in a three-dimensional format.
Three dimensional liver imaging is of most practical value if a resection ofone or more segments or sectors is considered, especially in the righthemiliver.
In these cases, 3D liver imaging can demonstrate the precise location of thescissuras to the surgeon pre-operatively.
The 8 anatomical points of interest: 注意下面8个解剖标志
the inferior vena cava, the right hepatic vein, the medial hepatic vein, theleft hepatic vein, the deep ligament venosum,
the superficial ligament venosum, the left lobe tip and the right portal vein
Figure 1: Definition of liver's segments (left) and sample of liver surgeryplanification (right).
圖12. 肝臟的解剖節段 A. 前表面; B. 后表面
