Dennis Lee, MD
Dennis Lee, MD
Dr. Lee was born in Shanghai, China, and received his college and medical training in the United States. He is fluent in English and three Chinese dialects. He graduated with chemistry departmental honors from Harvey Mudd College. He was appointed president of AOA society at UCLA School of Medicine. He underwent internal medicine residency and gastroenterology fellowship training at Cedars Sinai Medical Center.
In this Article
What is the relationship of sludge to gallstones?
Sludge is a common term that is applied to an abnormality of bile that is seen with ultrasonography of the gallbladder. Specifically, the bile within the gallbladder is seen to be of two different densities with the denser bile on the bottom. The bile is denser because it contains microscopic particles, usually cholesterol or pigment, embedded in mucus. (The mucus is secreted by the gallbladder.) Over time, sludge may remain in the gallbladder, it may disappear and not return, or it may come and go. As discussed previously, these particles may be precursors of gallstones, and they occur often in some situations in which gallstones frequently appear, for example, rapid weight loss, pregnancy, and prolonged fasting.
Nevertheless, it appears that sludge goes on to become gallstones in only a minority of individuals. Just to make matters more difficult, it is not clear how often - if at all - sludge alone causes problems. Sludge has been blamed for many of the same symptoms as gallstones-biliary colic, cholecystitis, and pancreatitis, but often these symptoms and complications are caused by very small gallstones that are missed by ultrasonography. Moreover, it is possible that these gallstone-like symptoms and complications are actually caused by small gallstones that have passed through the bile ducts and into the intestine rather than the sludge itself. Thus, there is uncertainty about the significance of sludge.
It is clear, however, that sludge is not the equivalent of gallstones. The practical implication of this uncertainty is that unless an individual's symptoms are typical of gallstones, sludge should not be considered as the cause of the symptoms.
How are gallstones diagnosed?
Gallstones are diagnosed in one of two situations.
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 not as useful compared to 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. On 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.
For transabdominal ultrasonography, the transducer is placed directly on the skin of the abdomen. 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:
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 the bile ducts.
Endoscopic ultrasonography (EUS)
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. EUS also is better in 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 a small risk of complications such as those associated with the use of intravenous sedation, and intestinal perforation by the endoscope. Fortunately, transabdominal ultrasonography usually gives most of the information that is necessary, and endoscopic ultrasonography needed only infrequently. Endoscopic ultrasonography also is a better way than transabdominal ultrasound to evaluate the pancreas.
Magnetic resonance cholangio-pancreatography (MRCP)
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.
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 the emptying of the gallbladder. Some patients with gallstones have had gallbladder inflammation 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)
The procedure is performed by using a long, flexible, side 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.
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 important 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 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
Duodenal biliary drainage
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 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 iodine to be absorbed, excreted, and concentrated.
Unlike ultrasonography, the OCG also cannot give information about the presence of non-gallstone related diseases. 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)
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 sufficiently 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.
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