Used by itself, or in conjunction with magnetic resonance (MR) and computed tomography (CT), ultrasound (US) can provide critical diagnostic information. US is nonionizing, portable, and often less expensive than other modalities. In addition, ultrasound is dynamic, allowing for the acquisition of cine clips and the application of maneuvers that can be critical in the diagnosis of certain pathologies such as acute cholecystitis. Furthermore, flow velocity within a vessel can be examined using Doppler sonography. Although information related to flow in vessels can be obtained with MR and to a lesser extent with contrast‐enhanced CT, the ease of ultrasound makes it the preferred modality for vascular pathology.

Ultrasound is user dependent, requiring the imager to obtain pertinent images of the patient’s anatomy, rather than full abdominal cross‐sections as in CT or MR. Images obtained are affected by the patient’s body habitus, respiratory motion, and sonographic artifacts, requiring adjustment and compensation by the performing imager. For example, air within the gastrointestinal tract creates posterior shadowing, obscuring deeper structures (Figure 87.1). As a result, the imager may have to use a different approach (sonographic window) or have the patient change position. These user‐dependent effects are typically greater with US than with MR or CT.

Liver

Primary indications for liver sonography include evaluation of diffuse parenchymal disease, focal liver mass, vascular disease, trauma, and transplantation.

Parenchymal diseases such as fatty liver and cirrhosis have typical sonographic appearances that are useful in confirming the clinical diagnosis. Hepatic steatosis commonly appears as a diffusely echogenic liver, but fatty infiltration may also appear geographic or focal within the liver. Conversely, areas of focal fatty sparing appear hypoechoic and appear in typical locations such as the gallbladder fossa (Figure 87.2). A nodular liver contour, coarsened hepatic echotexture, small liver size, and the presence of ascites can support a diagnosis of cirrhosis. Hepatitis has a nonspecific appearance on US, and often presents with a normal liver ultrasound. One presentation that has been described is the “starry sky” appearance related to edema within the portal triads (Figure 87.3), although this is nonspecific.

Although sonography is less sensitive than CT or MRI in detecting focal liver masses, it is a viable initial screening tool. Although CT or MR are preferred, US can be used in the screening of cirrhotic patients for hepatocellular carcinoma. Sonography is also frequently used to characterize abnormalities found on other imaging modalities such as CT or MRI, primarily by characterizing lesions as either cystic or solid. Common benign liver masses such as liver cysts (Figure 87.4, in a patient with autosomal dominant polycystic kidney disease) have typical sonographic appearances that allow for confident diagnoses. Masses with nonspecific imaging characteristics, such as focal nodular hyperplasia (Figure 87.5), often require further imaging with MR with a hepatobiliary contrast agent. When multiple solid lesions are present, especially in the setting of a known primary malignancy, metastatic disease should be considered (Figure 87.6). Hepatocellular carcinoma may have associated vascular involvement of the portal and hepatic veins, and US can be used to evaluate for extension of tumor thrombus into these vessels (Figure 87.7).

Doppler sonography is the first‐line modality in evaluation of hepatic vascular disease. A dedicated liver doppler evaluates the hepatic arteries (Figure 87.8), portal veins, hepatic veins, and inferior vena cava. It is a noninvasive method to detect the sequela of cirrhosis and the alterations of hemodynamics seen in portal hypertension, such as slow flow within the portal vein, portal vein thrombosis, development of corkscrew hepatic arteries (Figure 87.9) in response to the diminished flow in the portal vein, and cavernous transformation after long‐standing portal vein thrombosis (Figure 87.10). In patients with transjugular intrahepatic portosystemic shunts (TIPS), sonography can readily detect complications such as TIPS stenosis or occlusion. A normal TIPS is seen in Figure 87.11 and a stenosed TIPS in Figure 87.12. Sonography is also an important screening tool for posttransplant vascular complications and is helpful in detecting signs of vascular compromise before catastrophic loss of the transplant allograft (Figures 87.13–87.16). Hepatic vein occlusion may be seen in the setting of Budd–Chiari syndrome (Figure 87.17).

Ultrasound can be used to perform image‐guided interventions, such as abscess drainage, biopsy, and tumor ablation.

Gallbladder and biliary tract

Common indications for right upper quadrant abdominal ultrasound include evaluation for gallstones, cholecystitis, biliary ductal dilation, or choledocholithiasis.

Ultrasound can be used to evaluate for the presence of both intrahepatic (Figure 87.18) and extrahepatic biliary ductal dilation. If present, US can directly visualize causes of biliary obstruction, such as biliary stones or a pancreatic head mass. Patients with ultrasound examinations featuring biliary dilation without a visualized cause should be referred for magnetic resonance cholangiopancreatography (MRCP) or endoscopic retrograde cholangiopancreatography (ERCP). After ERCP and sphincterotomy, air may be present in the biliary tree, which can be visualized on US (Figure 87.19).

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