Diagnosis of Gallbladder Disease
Abdominal x-rays are not used to diagnose gallbladder disease. Only about 20% of gallstones are dense enough to be seen on x-ray, most blend in with the soft tissue structures of the abdomen.
Before the advent of ultrasound, the imaging test most used to visualize the gallbladder was the oral cholecystogram. In this test, an oral contrast agent (dye) was given to the patient the night before the test and would be flushed from the body through the gallbladder and bile ducts. When the agent appeared in the gallbladder, the radiologist used fluoroscopic equipment to look for stones. Lighter gallstones would be present within the gallbladder fluid. If the dye concentrated in the gallbladder, it indicated that the organ was functioning to some extent. Conversely, if the dye didn't appear in the gallbladder, the gallbladder was not functioning properly and perhaps should be removed.
The oral test was able to detect problems in the gallbladder, but was not able to detect problems in other parts of the bile system, such as the main bile duct. To detect other problems, intravenous cholangiogram (IVC) was used. This test involved the injection of a contrast agent, which caused side effects, such as nausea and rare life-threatening reactions. IVC involved special x-rays called tomograms that provided good images of the main bile ducts, enabling the radiologist to detect gallstones. In some cases, however, the images were inadequate due to technical problems, poor uptake of the dye by the liver, and other issues.
In most cases, ultrasound is the first imaging test for gallbladder and bile duct abnormalities. This test is non-invasive, uses no dyes, and is not painful. Ultrasound produces good images of the small ducts in the liver and the higher part of the major bile duct. However, the lower part of the duct, where it enters the GI tract, is where gallstones often get stuck. This lower part is close to the gastrointestinal (GI) tract and air produced in the GI tract deflects the sound waves. If ultrasound cannot detect the condition, other tests that can add valuable information.
Radionuclide Biliary Scan
This nuclear medicine test is not only an imaging test, but a function test as well. The patient is given an injection of a radioactive tracer and then imaging is done under a camera for up to several hours, but usually for no more than 30 to 45 minutes. From this test, the radiologist can determine if the isotope is picked up and excreted by the liver and can often tell if the cystic duct is blocked because, if it is, the gallbladder does not receive any radioactive material. The radiologist can also see whether or not the common bile duct is blocked. Ordinarily, the tracer should pass right through this duct and end up in the GI tract within a short period of time. If it gets stuck and is not seen in the GI tract, it can be assumed that the main duct is blocked.
In most cases, CT scan is not used to detect gallstones, but this imaging test does have its uses in the biliary system. First of all, the entire main duct can be seen using CT scan because unlike ultrasound, air in the GI tract does not interfere with CT. High-speed CT with computer-assisted reformatting capabilities allows the radiologist to move quickly through numerous images. The ability of CT to find stones in the common bile duct approximates ultrasound. In general, CT scan is a better test for more complicated problems, although it may be used together with ultrasound.
Transhepatic Cholangiogram (THC)
This interventional procedure involves placing a small needle into the liver and injecting dye into the bile ducts. THC is a very good test for evaluating the bile duct, but this test has definite risks. The improvements in ultrasound and CT imaging, as well as the emergence of MRI, were important factors in reducing the number of routine transhepatic cholangiograms.
Endoscopic Retrograde Cholangiopancreaticogram (ERCP)
Endoscopic retrograde cholangiopancreaticogram (ERCP) is often performed by gastroenterologists or surgeons, and not by radiologists. This test involves putting a tube into the patient's mouth, down the throat, into the stomach, through the duodenum and then, into the common bile duct. ERCP is performed with the patient sedated.
Looking through the tube, the gastroenterologist is able to locate the hole in the duodenum where the bile comes in from the common bile duct. A smaller tube or catheter is passed through this hole and contrast material is injected. The contrast agent (dye) also can be injected into the pancreatic duct, showing that ductal system as well.
The thick endoscopic tube affords visualization and other things as well. If the problem is a stone in the lower bile duct, the gastroenterologist can often put a basket into the tube and snare the stone and remove it. If the problem is tumor, the endoscopist can insert a biopsy device and remove a small piece of tissue for review by the pathologist. Finally, the endoscopist can help open the connection between the common bile duct and the duodenum by cutting the muscle that encircles the valve (sphincterotomy)—allowing stones that would have been trapped at the junction to flow right on through.
Magnetic Resonance Imaging (MRI scan)
Magnetic resonance imaging has spawned the new field of MRI cholangiography. With or without contrast material, MRI is able to show the bile in the bile ducts from many different angles. Some believe that MRI is about as good a modality for detecting stones in the bile ducts as there is, excluding the much more interventional transhepatic cholangiogram. Problems with MRI include limited availability in certain areas, limited cholangiographic skills and experience, and relatively high costs.
If gallbladder stones are suspected, and ultrasound is usually performed. If more complicated issues concerning the gallbladder or bile ducts are suspected, a CT scan, an MRI scan, or both may be performed. A radionuclide biliary scan also may provide useful information. Interventional tests, such as ERCP or THC are performed for complicated and serious conditions.