Formation of Gallstones (Cholelithiasis)
The process of gallstone formation is referred to as cholelithiasis. It is generally a slow process, and usually causes no pain or other symptoms. The majority of gallstones are either the cholesterol or mixed type. Gallstones can range in size from a few millimeters to several centimeters in diameter.
Most gallstones are formed from cholesterol. Pigment stones are also very common; they are formed from a brown-colored substance called calcium bilirubinate. Patients can have a mixture of the two gallstone types.
Cholesterol Stones. Although cholesterol makes up only 5% of bile, about three-fourths of the gallstones found in the US population are formed from cholesterol. 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 (a condition called supersaturation), which can eventually form gallstones.
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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 bile becomes stagnant.
- The cells lining the gallbladder may not be able to efficiently absorb cholesterol and fat from bile.
- There are high levels of bilirubin. Bilirubin is a substance normally formed by the breakdown of hemoglobin in the red blood cells. It is removed from the body in bile. Some experts believe bilirubin may play an important role in the formation of cholesterol gallstones.
Pigment Stones. Pigment stones are composed of calcium bilirubinate. Pigment stones can be black or brown.
- Black stones form in the gallbladder and are the more common type. They represent 20% of all gallstones in the U.S. They are more likely to develop in people with hemolytic anemia (a relatively rare anemia in which red blood cells are destroyed) or cirrhosis (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.
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Review Date: 06/10/2010
Reviewed By: Reviewed by: Harvey Simon, MD, Editor-in-Chief, Associate Professor
of Medicine, Harvard Medical School; Physician, Massachusetts
General Hospital. Also reviewed by David Zieve, MD, MHA, Medical
Director, A.D.A.M., Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)
