Gallstone ileus is obstruction of the bowel due to impaction of one of more gallstones. To achieve this, stones usually have to be at least 2.5 cm in diameter.
A fistula develops between a gangrenous gallbladder and the duodenum or other parts of the gastrointestinal tract, allowing passage of the stone. Occasionally the stone may enter the intestine through a fistulous communication between the bile duct and the gastrointestinal tract. Stones less than 2.5 cm in diameter may traverse the alimentary canal without causing obstruction. When the gallstone lodges in the duodenum and causes gastric outlet obstruction, it is called Bouveret's syndrome.
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