Gallstones form when bile, which is stored in the gallbladder, hardens into pieces of stone-like material. About 75% of gallstones are composed of cholesterol salts, while the remaining 25% are made up of bilirubin salts, a bile pigment. Gallstones can be as small as a grain of sand or as large as a golf ball. The gallbladder can develop just one large stone, hundreds of tiny stones, or almost any combination.

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Gallstones can block the normal flow of bile if they lodge in any of the ducts that carry bile from the liver to the small intestine. Bile trapped in these ducts can cause inflammation in the gallbladder, the ducts, or, rarely, the liver.

Gallstones can cause several related problems including:

• Gallstone pancreatitis—A gallstone blocks the opening to the pancreatic duct, and digestive enzymes become trapped in the pancreas causing extremely painful inflammation.
• Biliary colic—The pain is caused by a gallstone stuck in the bile duct, a tube that carries bile to the small intestine.
• Cholecystitis—A stone is caught in the bile duct, causing inflammation of the gallbladder.
• Cholangitis—This is an infection of the bile ducts.
• Gallstone ileus—In this condition, a large stone breaks through the gallbladder wall into the stomach, small intestine, or large intestine.

Gallstones are a common medical problem; about 10% to 15% of the adult population of the United States has gallstones. However, about 80% of people who have gallstones have no symptoms. This condition is referred to as “silent” gallstones and does not require treatment.