Cholescintigraphy (HIDA Scan)

Cholescintigraphy is a test done by nuclear medicine physicians to diagnose obstruction of the bile ducts (for example, by a gallstone or a tumor), disease of the gallbladder, and bile leaks. It sometimes is referred to as a HIDA scan or a gallbladder scan.

For cholescintigraphy, a radioactive chemical is injected intravenously into the patient. The test chemical is removed from the blood by the liver and secreted into the bile produced by the liver. The test chemical then disperses everywhere the bile goes into the bile ducts, the gallbladder, and the intestine. A camera that senses radioactivity (like a Geiger counter) is then placed over the patient's abdomen and a "picture" of the liver, bile ducts, gallbladder, and surrounding areas is obtained which corresponds to where the radioactive chemical has traveled within the bile-filled liver, bile ducts, and gallbladder. Cholescintigraphy takes approximately two hours.

Various patterns of radioactivity can be seen following the injection of the radioactive chemical, and each has a different meaning. If the test chemical is not detected in the liver, a diseased liver is probably indicated. If the chemical is absorbed by the liver but not secreted into the bile ducts, there probably is a complete obstruction of the bile ducts exiting the liver. When the test chemical fails to appear in the gallbladder, but is detected in the intestine, there probably is an obstruction of the cystic duct leading to and from the gallbladder. (Obstruction is most commonly caused by gallstones and, less commonly, by tumors. Parasites and blood clots also may obstruct infrequently.) Finally, if the chemical appears outside the liver, bile ducts, gallbladder, or intestine, there probably is a bile leak from the bile ducts or gallbladder.

Cholescintigraphy is most commonly used to diagnose problems with the gallbladder when other more commonly performed tests, particularly ultrasonography, are normal or non-diagnostic. Cholescintigraphy can be modified with the addition of an intravenous injection of cholecystokinin, the hormone that is normally released by the body after a meal. This hormone causes the gallbladder to contract and squeeze out its bile into the intestine. Reduced contraction of the gallbladder following cholecystokinin (i.e., reduced emptying of the radioactivity from the gallbladder) may mean that there is disease of the gallbladder itself, particularly inflammation or scarring of the wall.

Nonvisualization (the failure of the gallbladder to appear on a cholescintigraphy scan) of the gallbladder occurs because of disease of the gallbladder, particularly gallstones. However, nonvisualization does not necessarily mean that the obstruction is the cause of the patient's problem. For example, patients with gallstones often have a nonvisualizing gallbladder due to obstruction of the cystic duct, but the obstruction causes no symptoms. Thus, cholescintigraphy is helpful only if the patient's problem is likely based on the history and physical examination be due to disease of the gallbladder or bile ducts.

With the use of cholecystokinin, poor contraction of the gallbladder can be seen in some normal individuals. Therefore, reduced contraction does not always mean that the gallbladder is diseased. Again, cholescintigraphy with cholecystokinin is helpful only if the patient's problem is likely on the history and physical examination due to disease of the gallbladder or bile ducts.

Another limitation of cholescintigraphy is that this test does not work when the patient's serum bilirubin is greater than 4 mg/dl.

There are few side effects to cholescintigraphy. Reactions to the radioactive chemical and cholecystokinin are rare. The amount of radioactivity that patients are exposed to is small. The radioactive compound is eliminated in the stool, and the radioactivity deteriorates rapidly within hours.

Other common means of evaluating the gallbladder and bile ducts include ultrasonography and computerized tomography (CT or CAT scan). Cholangiography, either percutaneous (through the skin) or endoscopic (ERCP) (inserted down the throat), is a radiological procedure in which dye is injected into the gallbladder and bile ducts and then X-rays are taken. Newer procedures include endoscopic ultrasonography and magnetic resonance imaging (MRI) cholangiography. Oral cholecystography in which X-rays are taken of the gallbladder following ingestion of a dye that is concentrated in the gallbladder, is currently rarely done.