ile formation is the only significant pathway for elimination of excess cholesterol from the body, either as free cholesterol or as bile salts. Cholesterol is rendered water-soluble by aggregation with bile salts and lecithins. When cholesterol concentrations exceed the solubilizing capacity of bile (supersaturation), cholesterol can no longer remain dispersed and crystallizes out of solution. Cholesterol gallstone formation is enhanced by hypomobility of the gallbladder (stasis), which promotes nucleation, and by mucus hypersecretion, with consequent trapping of the crystals, thereby enhancing their aggregation into stones.
Formation of pigment stones is more likely in the presence of unconjugated bilirubin in the biliary tree, as occurs in hemolytic anemias and infections of the biliary tract. The precipitates are primarily insoluble calcium bilirubinate salts.