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Gallstones and gallbladder disease

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of gallstones.

Alternative Names

Cholecystitis; Choledocholithiasis; Bile duct stones

Introduction

Gallstones are small, hard pellets that can form in the gallbladder, a sac-like organ that lies under the liver on the right side of the abdomen. Most people with gallstones don't even know they have them. But in some cases a stone may cause the gallbladder to become inflamed, resulting in pain, infection, or other serious complications.

Bile and the Gallbladder

The formation of gallstones is a complex process that starts with bile , a fluid composed mostly of water, bile salts, lecithin (a fat known as a phospholipid), and cholesterol. (Most gallstones are formed from cholesterol.)

• Bile is important for the digestion of fat. It is first produced by the liver and then secreted through tiny channels that eventually lead into a larger tube called the common bile duct , which leads to the small intestine.

• Only a small amount of bile drains directly into the small intestine, however. Most flows into the gallbladder through the cystic duct , which is a side extension off the common bile duct. (This system of ducts through which bile flows is called the biliary tree).

• The gallbladder is a 4-inch sac with a muscular wall that is located under the liver. Here, most of the bile fluid (about 2 to 5 cups a day) is removed, leaving a few tablespoons of concentrated bile.
• The gallbladder serves as a reservoir until bile is needed in the small intestine to digest fats. This need is triggered by a hormone called cholecystokinin , which is released when food enters the small intestine.
• Cholecystokinin signals the gallbladder to contract and deliver bile into the intestine. The force of the contraction propels the bile back down the common bile duct and then into the small intestine, where it emulsifies (breaks down) fatty molecules.
• This part of the digestive process enables the emulsified fat along with important fat-absorbable nutrients (e.g., vitamins A, D, E, and K) to pass through the intestinal lining and enter the blood stream.

Formation of Gallstones (Cholelithiasis)

Gallstones can range from a few millimeters to several centimeters in diameter. Most are formed from cholesterol. Pigments stones are the second most common type of gallstones (approximately 15% of stones are pigment stones ). Patients can also have mixture of these two. Pigment stones are formed from a brown-colored substance called calcium bilirubinate.

Cholesterol Stones. Although cholesterol makes up only 5% of bile, about three-quarters of the gallstones found in the US population are formed from this substance. Cholesterol gallstones typically form in the following way:

• Cholesterol is not very soluble, so in order to remain suspended in fluid it must be transported within clusters of bile salts called micelles . If there is an imbalance between these bile salts and cholesterol, then the bile fluid turns to sludge. This thickened fluid consists of a mucus gel containing cholesterol and calcium bilirubinate.
• If the imbalance worsens, cholesterol crystals form (called supersaturation ), which can eventually form gallstones.
• This process of gallstone formation is referred to as cholelithiasis . It is very slow and most often painless.

Supersaturation and cholelithiasis can occur as a result of various abnormalities, although the cause is not entirely clear. There are many events that may promote cholelithiasis.

• The liver secretes too much cholesterol into the bile.
• The gallbladder may not be able to empty normally, so that the bile becomes stagnant.
• The cells lining the gallbladder may not be able to absorb cholesterol and fat from bile efficiently.
• High levels of bilirubin have been observed in patients with gallstones. Bilirubin is a substance normally formed by the breakdown of hemoglobin in the blood and it is excreted in bile. Some experts believe it may play an important role in cholesterol gallstones.

Pigment Stones. Pigment stones are composed of calcium bilirubinate, or calcified bilirubin. Pigment stones can be black or brown.

• Black stones form in the gallbladder and are the more common type. In fact, they represent 20% of all gallstones in the US. They are more likely to develop in people with hemolytic anemia (a relatively rare anemia where red blood cells are destroyed) or cirrhosis (a scarred liver).
• Brown pigment stones are more common in Asian populations. They contain more cholesterol and calcium than black pigment stones and are more likely to occur in the bile ducts. Infection plays a role in the development of these stones. One report suggested that bacteria or other microorganisms may trigger oxidation--a damaging chemical process in the body--which, in this case, can cause changes that lead to pigment stone formation.

Choledocholithiasis

Gallstones can also be present in the common bile duct. This is called choledocholithiasis.

Secondary Common Bile Duct Stones. In most cases, common bile duct stones originally form in the gallbladder and pass into the common duct (called secondary stones). Choledocholithiasis occurs in about 10% of patients who have gallstones.

Primary Common Bile Duct Stones. In less common cases, the stones form in the common duct itself (called primary stones). Primary common duct stones are usually of the brown pigment type and are more likely to cause infection than secondary common duct stones.

Gallbladder Diseases Without Stones

Gallbladder disease can occur without stones, a condition called acalculous gallbladder disease. It can be acute (arising suddenly, often as a one-time occurrence) or chronic (persistent).

• Acute acalculous gallbladder disease usually occurs in patients who are very ill from other disorders. In such cases, inflammation occurs in the gallbladder, usually from a diminished blood supply or an impaired ability to contract and empty its bile (i.e. impaired motility).
• Chronic acalculous gallbladder disease (also called biliary dyskinesia) appears to be caused by muscle defects or other problems in the gallbladder that cause impaired motility.

Diagnosing Acalculous Gallbladder Disease

Diagnosing Acute Acalculous Gallbladder Disease. Symptoms are similar to acute cholecystitis with gallstones, but they may be obscured by other medical conditions, since patients with this condition are often critically ill with other illnesses.

Diagnosing Chronic Acalculous Gallbladder Disease. Chronic acalculous gallbladder disease is usually diagnosed when a patient complains of gallbladder symptoms but there is no evidence of stones using standard imaging techniques. (More than half of patients initially diagnosed with this disease, however, are eventually shown to have small stones or gallbladder sludge.) The patient is given the hormone cholecystokinin octapeptide (CCK), which induces gallbladder contraction, followed by a radioisotope scan that determines if the gallbladder is emptying correctly. If the gallbladder demonstrates difficulty releasing bile, doctors usually consider the diagnosis confirmed.

Treatment for Acalculous Gallbladder Disease

Treatment for Acute Acalculous Gallbladder Disease. Acute acalculous gallbladder disease has a very high rate of serious complications (gangrene, perforation, and pus in the gallbladder), so emergency removal of the gallbladder is warranted.

Treatment for Chronic Acalculous Gallbladder Disease. Most patients (75% to 90%) diagnosed with chronic acalculous gallbladder disease are relieved of their symptoms by cholecystectomy (removal of the gallbladder). Between 10% and 23%, however, still experience pain. Surgery is most warranted in these patients when the symptoms are caused by impaired emptying of the gallbladder.

• Review Date: 6/12/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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