Although gallstones can form anywhere in the biliary tree, the most common point of origin is within the gallbladder. There are 3 types of gallstones, pure cholesterol, pure pigment, and mixed.
Under normal conditions, a delicate balance occurs among the levels of bile acids, cholesterol, and phospholipids. A disparity in this balance, especially with the supersaturation of cholesterol, predisposes patients to the formation of lithogenic bile and the subsequent development of cholesterol-type gallstones.
Pigmented gallstones are composed of calcium bilirubinate and appear in 2 major forms, black and brown. Hemolysis and liver disease are associated with the black stones; the brown, earthy stones more frequently are formed outside the gallbladder and often are associated with bacterial infections of the biliary tract.
Bile stasis predisposes to the formation of biliary sludge and eventual formation of gallstones and commonly is seen in patients who are unable to take enteral nutrition. Infection of the biliary tree (especially with certain beta-glucuronidase-producing bacteria, such as Escherichia coli and parasites) is associated with an increased risk of ductal stone development. Intestinal resection is associated with an increased incidence of gallstones. Contrary to expectation, these are mainly of the pigment variety.
Women are more likely to develop gallstones than men, with a ratio of 2:1. Classically, gallstones occur in obese, middle-aged women leading to the popular mnemonic, fat, fertile, forties. Oral contraceptive pills with high estrogen content increase the incidence of gallstones. The incidence increases with age