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.