LIVER ULTRASOUND NORMAL APPEARANCE
Category: Diagnostic Radiology
Abstract : The liver ultrasound - normal appearance The liver is a homogeneous, mid-grey organ on ultrasound. It has the same, or slightly increased echogenicity when compared to the cortex of the right kidney. Its outline is smooth, the inferior margin coming to a point anteriorly. The liver is surrounded by a thin, hyperechoic capsule, which is difficult to see on ultrasound unless outlined by fluid. Th
The liver ultrasound - normal appearance
The liver is a homogeneous, mid-grey organ on ultrasound. It has the same, or slightly increased echogenicity when compared to the cortex of the right kidney. Its outline is smooth, the inferior margin coming to a point anteriorly. The liver is surrounded by a thin, hyperechoic capsule, which is difficult to see on ultrasound unless outlined by fluid.
The smooth parenchyma is interrupted by vessels and ligaments and the liver itself provides an excellent acoustic window on to the various organs and great vessels situated in the upper abdomen. The ligaments are hyperechoic, linear structures; the falciform ligament, which separates the anatomical left and right lobes is situated at the superior margin of the liver and is best demonstrated when surrounded by ascitic fluid. It surrounds the left main portal vein and is known as the ligamentum teres as it descends towards the infero-anterior aspect of the liver. The ligamentum venosum separates the caudate lobe from the rest of the liver. The size of the liver is difficult to quantify, as there is such a large variation in shape between normal subjects and direct measurements are notoriously inaccurate. Size is therefore usually assessed subjectively. Look particularly at the inferior margin of the right lobe which should come to a point anterior to the lower pole of the right kidney. A relatively common variant of this is the Reidels lobe, an inferior elongation of segment VI on the right. This is an extension of the right lobe over the lower pole of the kidney, with a rounded margin, and is worth remembering as a possible cause of a palpable right upper quadrant mass. To distinguish mild enlargement from a Reidels lobe, look at the left lobe. If this also looks bulky, with a rounded inferior edge, the liver is enlarged. A Reidels lobe is usually accompanied by a smaller, less accessible left lobe.
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, 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. 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. Systematic scanning through the liver, in transverse section, identifies the main landmarks of the hepatic veins 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.
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