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ABDOMINAL ULTRASOUND
Figure 2.16 LS through the right lobe, demonstrating a
Reidel’s lobe extending below the right kidney. (Compare
with the normal liver in Figure 2.1.)
The segments of the liver
It is often sufficient to talk about the ‘right’ or
‘left’ lobes of the liver for the purposes of many
diagnoses. However, when a focal lesion is identified,
especially if it may be malignant, it is useful
to locate it precisely in terms of the surgical segments.
This allows subsequent correlation with
other imaging, such as computerized tomography
(CT) or magnetic resonance imaging (MRI), and
is invaluable in planning surgical procedures.
The segmental anatomy system, proposed by
Couinaud in 1954, 2 divides the liver into eight
segments, numbered in a clockwise direction.
They are divided by the portal and hepatic veins
and the system is used by surgeons today when
planning surgical procedures (Fig. 2.17). This system
is also used when localizing lesions with CT
and MRI.
Identifying the different segments on ultrasound
requires the operator to form a mental threedimensional
image of the liver. The dynamic nature
of ultrasound, together with the variation in planes
of scan, makes this more difficult to do than for CT
or MRI. However, segmental localization of
hepatic lesions by an experienced operator can be as
accurate with ultrasound as with MRI. 3 Systematic
scanning through the liver, in transverse section,
identifies the main landmarks of the hepatic veins
(Fig. 2.11) separating segments VII, VIII, IV and
II in the superior part of the liver. As the transducer
is moved inferiorly, the portal vein appears, and
below this segments V and VI are located.
Right hepatic vein
Middle hepatic vein
Left hepatic vein
VIII
VII
IV
II
III
V
I
Falciform ligament
Figure 2.17 The surgical
segments of the liver (after
Couinaud 2 ).
VI
Portal vein