Diagnosis of Gallstones

Gallstones are diagnosed in one of two situations.

• The first is when there are symptoms or signs that suggest gallstones, and the diagnosis of gallstones is being pursued.

• The second is coincidentally while a non-gallstone-related medical problem is being evaluated.
  

Ultrasonography is the most important means of diagnosing gallstones. Standard computerized tomography (CT or CAT scan) and magnetic resonance imaging (MRI) may occasionally demonstrate gallstones; however, they are poor for doing so compared with ultrasonography.

Ultrasonography
Ultrasonography is a radiological technique that uses high-frequency sound waves to produce images of the organs and structures of the body. The sound waves are emitted from a device called a transducer and are sent through the body's tissues. The sound waves are reflected by the surfaces and interiors of internal organs and structures as "echoes." These echoes return to the transducer and are transmitted electrically onto a viewing monitor. From the monitor, the outline of organs and structures can be determined as well as their consistency, for example, liquid or solid.

There are two types of ultrasonography that can be used for diagnosing gallstones, 1) transabdominal ultrasonography and 2) endoscopic ultrasonography.

Transabdominal ultrasonography
For transabdominal ultrasonography the transducer is placed directly on the skin of the abdomen which has had a gel applied to it. The sound waves travel through the skin and then into the abdominal organs. Transabdominal ultrasonography is painless, inexpensive, and without risk to the patient. In addition to identifying 97% of gallstones in the gallbladder, abdominal ultrasonography can identify many other abnormalities related to gallstones. It can identify:

• the thickened wall of the gallbladder when there is cholecystitis,
• enlarged gallbladders and ducts due to obstruction of the ducts by gallstones,
• pancreatitis, and
• sludge.
  

Transabdominal ultrasonography also may identify diseases not related to gallstones that may be the cause of the patient's problem, for example, appendicitis. The limitations of transabdominal ultrasonography are that it can only identify gallstones larger than 4-5 millimeters in size, and it is poor at identifying gallstones in ducts.

Endoscopic ultrasonography
For endoscopic ultrasonography, a long flexible tube - the endoscope - is swallowed by the patient after he or she has been sedated with intravenous medication. The tip of the endoscope is fitted with an ultrasound transducer. The transducer is advanced into the duodenum where ultrasonographic images are obtained.

Endoscopic ultrasonography can identify gallstones and the same abnormalities as transabdominal ultrasonography; however, since the transducer is much closer to the structures of interest - the gallbladder, bile ducts, and pancreas - better images are obtained than with transabdominal ultrasonography. Thus, it is possible to visualize smaller gallstones with endoscopic than transabdominal ultrasonography. It also is better for identifying gallstones in the common bile duct.

Although endoscopic ultrasonography is in many ways better than transabdominal ultrasonography, it is expensive, not available everywhere, and carries the small risks of intravenous sedation and intestinal perforation by the endoscope. Fortunately, transabdominal ultrasonography usually gives all of the information that is necessary, and endoscopic ultrasonography is infrequently needed. Endoscopic ultrasonography also is a better way than transabdominal ultrasound to evaluate the pancreas.

Magnetic resonance cholangio-pancreatography (MRCP)

Magnetic resonance cholangio-pancreatography or MRCP is a relatively new modification of magnetic resonance imaging (MRI) that allows the bile and pancreatic ducts to be examined.

• For MRCP, the patient is placed in a strong magnetic field that aligns (magnetizes) the protons in the molecules of water in the tissues. (Protons are parts of the atoms that make up water molecules. All tissues of the body contain water though they contain different amounts of water.)
  
• Energy-carrying radio waves then are passed through the tissues, and the energy is absorbed by the water's protons.
• The radio waves then are turned off, and the protons release the energy they absorbed.
• The released energy is used to form an image of the tissues and organs of the body.
• The MRI separates tissues and organs based on their concentration of water. Since different tissues contain different amounts of water, the MRCP is very good at providing images of organs and tissues.
• Since bile is mostly water, MRCP gives an excellent image of bile within the gallbladder and bile ducts. The pancreatic duct, which, like the bile ducts, is filled with a watery fluid, also is well-seen.
  

Thus, the procedure is called cholangio- (referring to the bile ducts) pancreatography (referring to the pancreatic duct).

MRCP has in many instances replaced other procedures such as cholescintigraphy (HIDA scan) and endoscopic retrograde cholangiopancreatography (ERCP). It can identify gallstones in the bile ducts, obstruction of the ducts, and bile leaks. There are no risks to the patient with MRCP.

Cholescintigraphy (HIDA scan)

Cholescintigraphy is a procedure done by nuclear medicine physicians. It sometimes is referred to as a HIDA scan or a gallbladder scan.

• For a HIDA scan, a radioactive chemical is injected intravenously into the patient.
• The radioactive chemical is removed from the blood by the liver and secreted into the bile.
• The chemical then disperses everywhere that the bile goes-into the bile ducts, the gallbladder, the intestine, and any place else that bile goes.
• 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, and gallbladder is obtained which corresponds to where the radioactive chemical has traveled within, or outside of the bile-filled bile ducts, and gallbladder.
  

HIDA scans are used to identify obstruction of the bile ducts, for example, by a gallstone. They also may identify bile leaks and fistulas. There are no risks to the patient with HIDA scans.

Cholescintigraphy is also used to study emptying of the gallbladder. Some patients with gallstones have had inflammation of their gallbladders due to recognized or unrecognized episodes of cholecystitis. (There also are uncommon, non-gallstone-related causes of inflammation of the gallbladder.) The inflammation can result in scarring of the gallbladder's wall and muscle, which reduces the ability of the gallbladder to contract. As a result, the gallbladder does not empty normally. During cholescintigraphy, a synthetic hormone related to cholecystokinin (the hormone the body produces and releases during a meal to cause the gallbladder to contract) can be injected intravenously to cause the gallbladder to contract and squeeze out its bile and radioactivity into the intestine. If the gallbladder does not empty the bile and radioactivity normally, it is assumed that the gallbladder is diseased as a result of gallstones or non-gallstone related inflammation.

The problem with interpreting a gallbladder emptying study is that many people with normal gallbladders have abnormal emptying of the gallbladder. Therefore, it is hazardous to base a diagnosis of a diseased gallbladder on abnormal gallbladder emptying alone.

Endoscopic retrograde cholangio-pancreatography (ERCP)

ERCP is an x-ray procedure to examine the duodenum (the first portion of the small intestine), the papilla of Vater (a small nipple-like structure where the common bile and pancreatic ducts enter the duodenum), the bile ducts, the gallbladder and the pancreatic duct.
The procedure is performed by using a long, flexible, viewing instrument (a duodenoscope, a type of endoscope) about the diameter of a fountain pen. The duodenoscope is flexible and can be directed and moved around the many bends of the stomach and intestine. The video-endoscope, the most common type of duodenoscope, uses a thin wire with a chip at the tip of the instrument to transmit video images to a TV screen.

• First the patient is sedated with intravenous drugs.
• The duodenoscope then is inserted through the mouth, to the back of the throat, down the food pipe (esophagus), through the stomach and into the first portion of the small intestine (duodenum).
• Once the papilla of Vater is identified, a small plastic catheter (cannula) is passed through a channel in the duodenoscope into the papilla of Vater, and into the bile ducts and the pancreatic duct.
• Contrast material (dye) then is injected, and x-rays are taken of the bile ducts, gallbladder and/or the pancreatic duct.
  

ERCP can identify 1) gallstones in the gallbladder (though it is not particularly good at this) and 2) blockage of the bile ducts, for example, by gallstones, and 3) bile leaks. ERCP also may identify diseases not related to gallstones that may be the cause of the patient's problem, for example, pancreatitis or pancreatic cancer.

An advantage of ERCP is that instruments can be passed through the same channel as the cannula used to inject the dye to extract gallstones stuck in the common and hepatic ducts. This can save the patient from having an operation. ERCP has several important risks associated with it, including the drugs used for sedation, perforation of the duodenum by the duodenoscope, and pancreatitis (due to damage to the pancreas). If gallstones are extracted, bleeding also may occur.

Liver and pancreatic blood tests

When the liver or pancreas becomes inflamed or their ducts become obstructed, the cells of the liver and pancreas release some of their enzymes into the blood. The most commonly-measured liver enzymes in blood are aspartate aminotransferase (AST) and alanine aminotransferase (ALT). The most commonly-measured pancreatic enzymes in blood are amylase and lipase. Many medical conditions that affect the liver or pancreas cause these blood tests to become abnormal, so abnormalities cannot be used to diagnose gallstones. Nevertheless, abnormalities in these tests suggest there is a problem with the liver, bile ducts, or pancreas, and gallstones are a common cause of such abnormal tests, particularly during sudden obstruction of the bile or pancreatic ducts. Thus, abnormal liver and pancreatic blood tests direct attention to the possibility that gallstones may be present and causing the acute problem.

Duodenal biliary drainage

Duodenal biliary drainage is a procedure that occasionally can be useful in diagnosing gallstones, however, it is not often used. As previously discussed, gallstones begin as microscopic particles of cholesterol or pigment that grow in size. It is clear that some people who develop biliary colic, cholecystitis, or pancreatitis have only these particles in their gallbladders, yet the particles are too small to obstruct the ducts. There are two potential explanations for how obstruction might occur in this situation. The first is that a small gallstone has obstructed and then finally passed through the bile ducts into the intestine. The second is that particles passing through the bile ducts can "irritate" the ducts, causing spasm of the muscle within the walls of the ducts (which obstructs the flow of bile) or inflammation of the duct that causes the wall of the duct to swell (and also obstructs the duct).

• For duodenal drainage, a thin plastic or rubber tube with several holes at its tip is passed through a patient's anesthetized nostril, down the back of the throat, through the esophagus and stomach, and into the duodenum where the bile and pancreatic ducts enter the small intestine. This is done with the help of x-ray (fluoroscopy).
• Once the tube is in place, a synthetic hormone related to cholecystokinin is injected intravenously. The hormone causes the gallbladder to contract and squeeze out its concentrated bile into the duodenum.
• The bile then is sucked up through the tube in the duodenum and examined for the presence of cholesterol and pigment particles under a microscope.
  

The risks to the patient of duodenal drainage are minimal. (There have been no reports of reactions to the synthetic hormone.) Nevertheless, duodenal drainage is uncomfortable.

A modification of duodenal drainage involves collection of bile through an endoscope at the time of an upper gastrointestinal endoscopy-either esophago-gastro-duodenoscopy (EGD) or ERCP.

Oral cholecystogram (OCG)

The oral cholecystogram or OCG is a radiologic (x-ray) procedure for diagnosing gallstones.

• For an OCG, the patient takes iodine-containing tablets for one or two nights in a row and then has an x-ray of his or her abdomen.
• The iodine is absorbed from the intestine, removed from the blood by the liver, and excreted into bile.
• In the gallbladder, the iodine becomes concentrated along with the bile.
• On the x-ray, the iodine, which is dense and stops x-rays, fills the gallbladder and outlines the gallstones which are not dense, and allow x-rays to pass through them. The ducts cannot be seen on the x-ray because the iodine is not concentrated in the ducts.
  

The OCG is an excellent procedure for diagnosing gallstones; it finds 95% of them. The OCG has been replaced, however, by ultrasonography because ultrasonography is slightly better at diagnosing gallstones and can be done immediately without waiting one or two days for the OCG's iodine to be absorbed, excreted, and concentrated.

The OCG also cannot give information about the presence of non-gallstone related diseases like ultrasonography. As would be expected, ultrasonography sometimes finds gallstones that are missed by the OCG. Less frequently, the OCG finds gallstones that are missed by ultrasonography.

For this reason, if there is a strong suspicion that gallstones are present but ultrasonography does not show them, it is reasonable to consider doing an OCG. An OCG should not be done in individuals who are allergic to iodine.

Intravenous cholangiogram (IVC)

The intravenous cholangiogram or IVC is a radiologic (x-ray) procedure that is used primarily for looking at the larger intrahepatic and the extrahepatic bile ducts. It can be used to locate gallstones within these ducts.

For an IVC, an iodine-containing dye is injected intravenously into the blood. The dye is removed from blood by the liver and excreted into bile. Unlike the iodine used in the OCG, the iodine in the IVC is concentrated enough in the bile ducts to outline the ducts and gallstones within them. The IVC is rarely used because it has been replaced by MRI cholangiography and endoscopic ultrasound . Moreover, occasional serious reactions to the iodine-containing dye can occur, which rarely may result in the death of the patient.