Abdominal Ultrasonography

1

List some of the most common indications for abdominal ultrasonography (US).

• Abdominal, flank, and/or back pain.

• Abnormal laboratory values (e.g., abnormal liver function tests).

• Palpable abdominal mass.

• Signs or symptoms referred from abdomen (e.g., jaundice or hematuria).

2

What is the sonographic appearance of the liver?

The liver is normally homogeneous in echotexture, equal to or slightly more echogenic than the renal cortex, and hypoechoic compared to the spleen and pancreas. Along the midhepatic line, the liver is normally <15.5 cm in length. The hepatic veins are readily visible sonographically and help define hepatic anatomy. The right hepatic vein divides the right hepatic lobe into anterior and posterior segments. The middle hepatic vein separates the anterior segment of the right hepatic lobe and the medial segment of the left hepatic lobe. The gallbladder also separates the anterior segment of the right lobe and the medial segment of the left lobe. The left hepatic vein divides the left hepatic lobe into medial and lateral segments ( Figure 62-1 ). The ligamentum teres also separates the medial and lateral segments of the left hepatic lobe.

3

How are the hepatic veins and portal veins differentiated on US?

Portal veins travel with hepatic arteries and bile ducts (the portal triad). A connective sheath surrounds this portal triad with resulting echogenicity of the portal vein walls. In contrast, the hepatic veins travel in isolation and have almost imperceptible walls (see Figure 62-1 ).

4

What is the most common cause of increased hepatic echogenicity?

Increased hepatic echogenicity is detected when the liver is considerably more echogenic than the kidney. The most common cause is hepatic steatosis. Other sonographic features of hepatic steatosis include finer and more compact echotexture and decreased transmission of sound waves such that the deeper aspect of the liver is difficult to visualize, as are the adjacent diaphragm and intrahepatic vessels. There are numerous causes of hepatic steatosis, including obesity, alcohol abuse, diabetes mellitus, corticosteroid use, malnutrition, and chemotherapy.

5

Describe the US appearance of acute hepatitis.

Acute hepatitis can result in liver edema, which manifests on US as diffusely decreased hepatic echogenicity with increased echogenicity of the portal triads (the “starry sky” sign). There can be associated hepatomegaly and gallbladder wall thickening.

6

Name and describe the US appearance of common benign and malignant focal hepatic lesions.

For the answer, see Table 62-1 , Figure 62-2 , and Figure 62-3 .

7

Describe the US appearance of a target lesion in the liver and its significance.

A target lesion on US is characterized as a hepatic lesion with an echogenic center and a peripheral hypoechoic rim (see Figure 62-3 ). This appearance has a high association with malignancy, including metastatic disease, hepatocellular carcinoma, and lymphoma. In contrast, lesions with a reverse target appearance (an isoechoic to hypoechoic center and a hyperechoic rim) are more commonly associated with a benign etiology, such as a hemangioma.

8

What are the sonographic features of cirrhosis?

The liver may be increased in size in the early stages of cirrhosis and later become small with relative enlargement of the caudate and/or left hepatic lobe. The liver has a nodular contour and a more echogenic and heterogeneous echotexture. Associated features of portal hypertension may be seen, which include ascites, splenomegaly, recanalization of the paraumbilical vein, and portal vein enlargement.

9

What is the appearance of gallstones on US?

US is the modality of choice for detecting gallstones. Gallstones appear as rounded echogenic structures in the gallbladder lumen with posterior acoustic shadowing. Stones smaller than 5 mm may not shadow but will still appear echogenic. Gallstones are also typically mobile. Gallstones may also be seen in association with biliary sludge, which appears as dependent, low-level layering echogenic material in the gallbladder ( Figure 62-4 ).

10

What is the “wall-echo-shadow” sign?

The “wall-echo-shadow” (WES) sign is the result of the gallbladder being filled with small stones, or a single giant stone. The hypoechoic nondependent gallbladder wall is first visualized (wall), followed by echogenic gallstones (echo), and then posterior acoustic shadowing (shadow), which obscures the remainder of the gallbladder ( Figure 62-5 ). The WES sign can be differentiated from air or calcification in the gallbladder wall, as in these cases, the normal hypoechoic gallbladder wall is not seen, only gallbladder fossa echogenicity with posterior acoustic shadowing.

11

Can tumefactive sludge and gallbladder polyps be differentiated from gallstones sonographically?

When sludge consolidates to form a mass, so-called tumefactive sludge, it is still typically mobile and avascular, which differentiates it from a polyp, and it does not shadow, which differentiates it from a gallstone. Gallbladder polyps can be as echogenic as are small gallstones, but they are nonmobile and do not shadow. Color Doppler flow can also sometimes be detected in a polyp.