Medical Health Encyclopedia

Ultrasound. Ultrasound is a simple, rapid, and noninvasive imaging technique. It is the diagnostic method most frequently used to detect gallstones and is the method of choice for detecting acute cholecystitis. The patient must not eat for six or more hours before the test, which takes only about 15 minutes. During the procedure, the doctor can check the liver, bile ducts, and pancreas and quickly scan the gallbladder wall for thickening (characteristic of cholecystitis).

Ultrasound detects gallstones as small as two millimeters in diameter with an accuracy of 90% to 95%. Some experts recommend that if an ultrasound does not detect stones, but gallstones are still strongly suspected, the test should be repeated.

Air in the gallbladder wall may indicate gangrene.

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Ultrasound does not appear to be very useful for identifying cholecystitis in symptomatic patients who do not have gallstones. In one study, ultrasound detected some gallbladder abnormalities, no matter what the cause of the abdominal pain. In only a few cases, however, were the symptoms actually caused by cholecystitis.

Ultrasound is also not as useful for common bile duct stones and cannot image the cystic duct. (Nevertheless, normal ultrasound results along with normal bilirubin and liver enzyme tests are very accurate indications that there are no stones in the common bile duct.)

An ultrasound variation called endoscopic ultrasound (EUS) is accurate and useful for patients with an intermediate risk for common bile ducts stones. Its accuracy is comparable to endoscopic retrograde cholangiopancreatography (ERCP), the standard for diagnosing stones in the common bile duct. However, if common duct stones are detected they cannot be removed. It is useful then when common bile duct stones are suspected but the patient is not clearly ill.