The treatment of gallbladder disease has been revolutionized by improvements in laparoscopic surgery as well as endoscopic and radiologic interventional techniques. Therapeutic success is dependent on accurate radiologic assessment of gallbladder pathology. This article describes recent technical advances in ultrasonography, multidetector computed tomography, magnetic resonance imaging, positron emission tomography, and scintigraphy, which have significantly improved the accuracy of noninvasive imaging of benign and malignant gallbladder disease. The imaging findings of common gallbladder disorders are presented, and the role of each of the imaging modalities is placed in perspective for optimizing patient management.
Recent technical advances in ultrasonography, multidetector computed tomography (CT), magnetic resonance imaging (MRI), and scintigraphy have significantly improved the accuracy of the noninvasive imaging of benign and malignant gallbladder pathology. Because of high diagnostic accuracy, wide availability, and ease of performance, ultrasonography and CT are the primary imaging tests for patients with suspected gallbladder and biliary tract pathology. MRI with magnetic resonance cholangiopancreatography (MRCP) is assuming an increasingly important role in the imaging armamentarium and has largely replaced diagnostic endoscopic retrograde cholangiopancreatography (ERCP). Evaluation of acute cholecystitis using hepatobiliary scintigraphy has diminished over the past decade. Positron emission tomographic (PET) imaging is being used with increased frequency to stage gallbladder neoplasms. This article presents the imaging findings of common gallbladder diseases, and the role of each of the imaging modalities is placed in perspective for optimizing patient management.
Cholelithiasis
The nature and size of a gallstone affects its imaging characteristics. Gallstones are comprised mainly of cholesterol, bilirubin, and calcium salts, with smaller amounts of protein and other materials including bile acids, fatty acids, and inorganic salts. In Western countries, cholesterol is the principal constituent of more than 75% of gallstones, with smaller amounts of calcium bilirubinate. Pure cholesterol stones contain more than 90% cholesterol and account for less than 10% of biliary calculi. The more cholesterol and less calcium a stone contains, the less likely will it be seen on CT scan, which best depicts predominantly calcified stones. Black or brown pigment stones consist of calcium salts of bilirubin and contain less than 25% cholesterol. These stones compose only 10% to 25% of gallstones in North America. These stones show a less-dramatic duct shadow than cholesterol or more calcified stones, particularly when present in the bile duct.
Plain Radiographic Findings
The abdominal plain radiograph is insensitive in depicting gallstones because only 15% to 20% are sufficiently calcified to be visualized. Oral cholecystography was the mainstay of gallstone detection for more than 50 years but was replaced in the late 1970s by ultrasonography.
Sonographic Findings
Ultrasonography is now the gold standard for the noninvasive diagnosis of cholelithasis. This imaging test is highly accurate (>96%), can be performed at the patient’s bedside, and does not require the use of ionizing radiation. Gallstones must fulfill 3 major sonographic criteria. They must (1) show an echogenic focus, (2) cast an acoustic shadow, and (3) seek gravitational dependence. Gallstones are accurately diagnosed when a 5 mm or larger defect meets all 3 major criteria. Stones smaller than 2 to 3 mm may be difficult to visualize. Small stones, however, are usually multiple in occurrence, assisting their detection.
Gallstones produce 3 patterns of shadowing. The first is a discrete shadow ( Fig. 1 A) emanating from a solitary stone. The second pattern is confluent shadowing because of multiple stones (see Fig. 1 B) or gravel that abut each other in the gallbladder. The third pattern, the wall-echo-shadow (WES) complex (see Fig. 1 C) occurs when a contracted gallbladder is completely filled with gallstones. These stones give an echogenic double arc appearance, which consists of 2 parallel arcuate hyperechoic lines separated by a thin hypoechoic space and distal acoustic shadowing. The more superficial hyperechoic arc represents reflections from gallstones, and the hypoechoic space in between represents either a small sliver of bile between the wall and the stones or a hypoechoic portion of the gallbladder wall. The WES sign must be differentiated from a partially collapsed duodenal bulb, porcelain gallbladder, emphysematous cholecystitis, xanthogranulomatous cholecystitis, and a calcified hepatic artery aneurysm.
