Ultrasonography in acute cholecystitis

Ultrasonography
US is a relatively inexpensive, noninvasive imaging modality used to confirm the presence of biliary ductal dilation . US, when performed correctly, may provide considerable information to assist the internist, surgeon, gastroenterologist, or interventional radiologist in the management of patients with hepatobiliary disease.

Though operator dependent, US is generally readily available in most medical institutions caring for patients with biliary disease. The normal gallbladder is an anechoic (fluid-filled) oval structure. The position of the gallbladder fundus is variable; however, the gallbladder neck has a fixed relationship with the main interlobar fissure of the liver. The wall of the gallbladder is a thin, smooth, echogenic line that should not exceed 3 mm. The gallbladder wall may appear abnormally thickened in the nonfasting state. Pathologic gallbladder wall thickening may be secondary to cholecystitis, hepatitis, hepatic failure, congestive heart failure, renal failure, neoplasm, or human immunodeficiency virus. The common hepatic duct is easily visualized in the porta hepatis as it crosses the undivided right portal vein. In most cases, the hepatic artery passes between the common hepatic duct and portal vein; however, in 10% to 15% of patients, the hepatic artery is located anterior to the common hepatic duct. The joining of the cystic duct with the common hepatic duct forms the common bile duct. The cystic duct is generally located posterior to the common hepatic duct and may travel a variable distance before joining the common hepatic duct. Within the hepatoduodenal ligament, the common bile duct is anterior and lateral to the portal vein. As the common bile duct travels caudally to the second portion of the duodenum, it assumes a more posterior position. On US, the normal diameter of the extrahepatic bile ducts may range from 4 to 8 mm. The size of the extrahepatic bile ducts may increase slightly with increasing patient age, after cholecystectomy, or bile duct surgery, or after endoscopic manipulation of the duct. The maximum upper limit of normal in the extrahepatic biliary tree after cholecystectomy is 10 mm. However, it is generally accepted that a duct that measures 6 mm or greater in symptomatic patients warrants further investigation. Intrahepatic bile ducts can be considered normal if they are less than 40% of the diameter of the accompanying portal vein or if they are 2 mm or less in diameter. Intrahepatic biliary dilation may appear as an alteration in the normal anatomic relationships in the portal triads and a confluence of tubular structures near the hilum of the liver. The appearance of peripheral intrahepatic duct dilation has been called the parallel channel sign Color-flow Doppler US is useful in this setting to confirm the presence of biliary dilation. Using color-flow Doppler US, one may differentiate between vessels and dilated biliary ducts. US accurately predicts the level of biliary obstruction in the majority of cases (92%), but it is less accurate in suggesting the correct cause (71%). There are many causes of biliary obstruction. These include stones, neoplasms, inflammatory disease, and congenital causes (rare). Newer noninvasive techniques include the use of tissue harmonic imaging to improve visualization of the bile ducts. US coupled with the use of CT or MRCP to determine extent of disease assists the interventional radiologist, gastroenterologist, or surgeon in planning therapy.

An ultrasonography of the gallbladder. Arrows indicate the acoustic shadows from stones in the gallbladder