The diagnosis of diseases of the liver, biliary tract, and pancreas optimally depends on using both clinical and radiographic data. Understanding the proper use of these data and ordering radiographic studies in the optimal sequence are helpful for making the diagnosis most efficiently. Frequently, the clinical presentation and associated laboratory work provide most of the clues for diagnosis. Physical examination, history, and pertinent laboratory values are often helpful in making the diagnosis or at least in providing clues for selecting the optimal radiographic studies. If clinical information is insufficient or if radiographic confirmation is necessary, plain films and contrast studies may be performed. Upright and supine plain radiographs are helpful for the detection of free air, calcifications, and other abnormalities. Contrast studies such as endoscopic retrograde cholangiopancreatography (ERCP), magnetic resonance cholangiopancreatography (MRCP) and percutaneous transhepatic cholangiography (PTC) are often helpful in analyzing diseases of the liver, biliary tree, and pancreas. For instance, pancreatic or biliary ductal systems, fistulae from these ductal systems, and associated abnormalities such as encasing tumors can be diagnosed by cholangiography.
Digital cross-sectional imaging, nuclear medicine (NM) and an important form of NM called positron emission tomography (PET), and angiography have provided considerable information in analyzing diseases of these organs, which cannot be directly visualized with plain radiography, even using traditional contrast material, that is, barium. Cross-sectional techniques consist of ultrasound (US), computed tomography (CT), and magnetic resonance (MR) imaging. This chapter reviews the use of cross-sectional imaging and, where pertinent, nuclear medicine and angiography to evaluate abnormalities of the liver, biliary tract, and pancreas.
Several modalities such as US, nuclear medicine, CT, and MR imaging are commonly used in diagnosing diseases of liver, pancreatic, or biliary ductal system. The detail of each technique has been described in Chapter 1, “Scope of Diagnostic Imaging.”
With US, normal organs are displayed as structures of different echogenicity. In general, fluid is anechoic (has no echoes). Soft tissue has echoes of mild to moderate intensity. Bone has extremely strong echoes. Abnormal organs are displayed as areas of diffuse inhomogeneity or as focal regions of decreased or increased echogenicity within the organ. The normal appearances of the liver, biliary system, and pancreas have been well established. Echogenicity of the organs in the abdomen is evaluated in relation to other nearby organs. The pancreas is typically the most echogenic organ in the upper abdomen, followed by the liver. The liver typically has homogeneous parenchymal detail (Figure 11-1). Numerous intrahepatic vessels including portal veins and hepatic veins are easily seen within the liver. The gallbladder appears as an anechoic pear-shaped structure along the inferior aspect of the liver (Figure 11-2). It normally has a thin, homogeneous wall less than 3 mm in thickness. The degree of distention of the gallbladder varies with postprandial intervals. As is expected, it contracts after a meal and distends in the fasting state. The biliary ducts are thin tubes, the walls ...