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Anatomy of the liver segments

Robin Smithuis

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

Publicationdate May 7,
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 indepedent segments.
This classification will be presented here
with several illustrations.

Segmental anatomy

Segmental anatomy according
to Couinaud.Click image to enlarge.

Couinaud classification

The Couinaud classification of liver anatomy divides the liver into eight
functionally indepedent 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 liversegments.

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 (in French
'gauche et droite foie') 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.Click image to
enlarge.

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.Click image to
enlarge.

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
liverparenchyma.

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.

Traditional
Surgical Viewpoint of Liver Anatomy and Definition of the Couinaud
Segments

3-D tutorials of the Division of Physiologic Imaging, Dept. of Radiology,
Univ. of Iowa

Portal venous
and segmental anatomy of the right hemiliver: observations based on
three-dimensional spiral CT renderings

MS van Leeuwen, J Noordzij, MA Fernandez, A Hennipman, MA Feldberg and EH
Dillon
Department of Radiology, University Hospital Utrecht, The
Netherlands

Planning
of liver surgery using three dimensional imaging techniques.

van Leeuwen MS, Noordzij J, Hennipman A, Feldberg MA.
Department of
Radiology and Surgery, University Hospital Utrecht, The Netherlands.

Clinical and anatomical basis
for the classification of the structural parts of liver

Saulius Rutkauskas et al.
Clinic of Radiology, Institute of Anatomy,
Clinic of Surgery, Kaunas University of Medicine,
Lithuania