Page 1 of 1: liver- architecture

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the architecture of liver is divided into lobes by

1. bile duct
2. hepatic artery
3. hepatic vein
4. portal vein
5. lymphatics

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bile duct
hepatic artery
and
portal vein

whats the answer man.

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I) caudate/Spigel lobe
II) left posterolateral segment
III) left anterolateral segment
IVa) left superomedial segment
IVb) left inferomedial segment
V) right anteroinferior segment
VI) right posteroinferior segment
VII) right posterosuperior segment
VIII) right anterosuperior segment

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In both the traditional and the Couinaud classifications, the plane defined by the middle hepatic vein subdivides the liver into the true right and left lobes. A standard right or left lobectomy requires division along the plane of the middle hepatic vein. Segments IVa and IVb lie to the left of the plane while segments V and VIII lie to the right with VIII being superior to V. In the movie, the gallbladder is slightly brighter than the rest of the plane. Because the plane of the middle hepatic vein usually intersects the gallbladder fossa, Cantlie's line (the projection on the liver surface of a plane between the gallbladder and IVC) is generally a valid line of division between the right and left lobes. However, it is the vasculature that determines the true boundary.

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hepatic vein

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Great! Lo ji ! Aur bhi khub sara material !

Definition of the Couinaud Segments
Couinaud Liver Segments
The Couinaud classification divides the liver into 8 independent segments each of which has its own vascular inflow, outflow, and biliary drainage. Because of this division into self-contained units, each can be resected without damaging those remaining. For the liver to remain viable, resections must proceed along the vessels that define the peripheries of these segments. In general, this means resection lines parallel the hepatic veins while preserving the portal veins, bile ducts, and hepatic arteries that provide vascular inflow and biliary drainage through the center of the segment. [Gazelle]
Resecting only specific liver segments is especially useful in patients with hepatocellular carcinoma. Fifty to 75% of these patients have underlying liver cirrhosis and poor liver reserve. The surgical challenge in these patients is to resect enough liver to allow complete tumor resection while retaining all possible non-tumorous liver to prevent further loss of liver function. In support of the benefit of resections along segmental boundaries, MacIntosh has reported an operative mortality of 0-16% with segment based resections compared to mortalities of 20-60% in patients receiving traditional lobectomies or non-segment based wedge resections.

In Couinaud nomenclature, the plane defined by the right branch of the portal vein divides the anterior and posterior divisions of the right liver superiorly and inferiorly, thus dividing the right lobe into 4 segments (V-VIII). The medial segment of the left lobe can also be divided into two segments by the plane of the portal vein (IVa and IVb) [Bismuth]. While the portal vein plane has often been portrayed as transverse [Soyer], it may be oblique since the left branch runs superiorly and the right branch runs inferiorly. In addition to forming an oblique transverse plane between segments, the left and right portal veins branch superiorly and inferiorly to project into the center of each segment.
Segment 1: The Caudate Lobe

The most unique of the Couinaud segments is segment I which corresponds to the caudate lobe (also known as the Spigel lobe). It is located on the posterior surface of the liver adjacent to segment IV. Its medial and lateral boundaries are defined by the IVC and ligamentum venosum respectively.
Segment I is different than the other segments in that its portal inflow is derived from the left and right branches of the portal vein, and it often has its own short hepatic veins connecting directly to the IVC. The vessels of the caudate lobe are rarely seen on CT because they are small. Because of the extensive crossing of vessels and its position relative to the porta hepatis and IVC, segment I is not often resected. However, several examples exist in the literature [Lerut, Yamamoto].

In both the traditional and the Couinaud classifications, the plane defined by the middle hepatic vein subdivides the liver into the true right and left lobes. A standard right or left lobectomy requires division along the plane of the middle hepatic vein.

I) caudate/Spigel lobe
II) left posterolateral segment
III) left anterolateral segment
IVa) left superomedial segment
IVb) left inferomedial segment
V) right anteroinferior segment
VI) right posteroinferior segment
VII) right posterosuperior segment
VIII) right anterosuperior segment

Liver Segmental Anatomy
Robin Smithuis
From the Radiology Department of the Rijnland Hospital, Leiderdorp, the Netherlands
• Segmental Anatomy
• Couinaud classification
• Segments numbering
• Transverse Anatomy
• Caudate lobe
• Other Classifications and Variants
• Classical Anatomy
• Bismuth's classification
• Variations
back to overview print
Publicationdate: 7-5-2006
Liver Anatomy can be described using two different aspects: morphological Anatomy and functional Anatomy .
The traditional morphological Anatomy is based on the external appearance of the liver and does not show the internal features of vessels and biliary ducts branching, which are of obvious importance in hepatic surgery.
C. Couinaud (1957) divided the liver into eight functionally independent segments.
This classification will be presented here with several illustrations.
Segmental Anatomy

Segmental Anatomy according to Couinaud Couinaud classification
The Couinaud classification of liver Anatomy 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.
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 and left hemiliver).This plane runs from the inferior vena cava to the gallbladder fossa.
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 project into the center of each segment.
Because of this division into self-contained units, each segment can be resected without damaging those remaining. For the liver to remain viable, resections must proceed along the vessels that define the peripheries of these segments. This means, that resection-lines parallel the hepatic veins,
The centrally located portal veins, bile ducts, and hepatic arteries are preserved.

Clockwise numbering of the segments 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 frontal view.

On a frontal view of the liver the posteriorly located segments 6 and 7 are not visible. The illustrations above are schematic presentations of the liver segments.
In reality however the proportions are different.
On a normal frontal view the segments 6 and 7 are not visible because they are located 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 the right.
Couinaud divided the liver into a functional left and right liver ( by a main portal scissurae containing the middle hepatic vein. This is known as Cantlie's line.
Cantlie's line runs from the middle of the gallbladder fossa anteriorly to the inferior vena cava posteriorly.
On this illustration it looks as if the medial part of the left lobe is separated from the lateral part by the falciform ligament. However it actually is the left hepatic vein, that separates the medial part (segment 4) from the lateral part (segments 2 and 3).
The left hepatic vein is located slightly to the left of the falciform ligament.

LEFT: above the level of the left portal vein.
RIGHT: at the level of the left portal vein 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 the superior segments (2 and 4A) and the inferior segments (3 and 4B).
The left portal vein is at a higher level than the right portal vein.

LEFT: at the level of the right portal vein.
RIGHT: at the level of the splenic vein. The image on the far left is at the level of the right portal vein. At this level the right portal vein divides the right lobe of the liver into superior segments (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 portal vein.
At the level of the splenic vein, which is below the level of the right portal vein, only the inferior segments are seen (right image).

Hypertrophy of caudate lobe in a patient with livercirrhosis. Notice the small lobulated right hemiliver. Caudate lobe
The caudate lobe or segment 1 is located posteriorly. The caudate lobe is anatomically different from other lobes in that it often has direct connections to the IVC through hepatic veins, that are separate from the main hepatic veins.
The caudate lobe may be supplied by both right and left branches of the portal vein.
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 disease process and hypertrophied to compensate for the loss of normal liver parenchyma.
Other Classifications and Variants

There are many other anatomical and functional descriptions of the liver Anatomy .
In the classical description the external appearance of the liver is used to describe the Anatomy .
However there are many differences between this classical model and the fuctional 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 external appearance.
On the diaphragmatic surface, the ligamentum falciforme divides the liver into the right and left anatomic lobes, which are very different from the functional right and left lobes (or right and left hemiliver).
In this classical description, the quadrate lobe belongs to the right lobe of the liver, but functionally it is part of left lobe.

Bismuth's classification
This classification is very similar to the Couinaud classification, although there are small differences. It is popular in the United States, while Couinaud'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 pedicle in the centre.
The separation line between sectors contain a hepatic vein.
The hepatic veins and portal pedicels are intertwined, as are the fingers of two hands.
The left portal scissura divides the left liver into two sectors: anterior and posterior.
Left anterior sector consists of two segments: segment IV, which is the quadrate lobe and segment III, which is anterior part of anatomical left lobe.
These two segments are separated by the left hepatic fissure or umbilical fissure.
Left posterior sector consists of only one segment II. It is the posterior part of left lobe.
Variations
In the Couinaud classification little attention is given to the high prevalence of anatomical variations which occur, especially in the right hemiliver.
Using volumetric acquisition techniques, such as magnetic resonance imaging or spiral computed tomography scanning, detailed insight into the individual segmental Anatomy can now be obtained in a non-invasive manner (2,3).
The significance of this anatomical insight lies in the planning of anatomical resections, whereby the relationship between tumour and individual segmental Anatomy can be depicted in a three-dimensional format.
Three dimensional liver imaging is of most practical value if a resection of one or more segments or sectors is considered, especially in the right hemiliver.
In these cases, 3D liver imaging can demonstrate the precise location of the scissuras to the surgeon pre-operatively.

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