Diseases of the gallbladder Gallstones
Gallstones are extremely common and will affect one in three women and one in five men in Europe. The three major classes of gallstones-cholesterol stones, black pigment stones, and brown pigment stones-differ in their pathogenesis as well as in their composition.
Cholesterol and black pigment stones form only in the gallbladder, but brown pigment stones are formed in the bile ducts after bacterial infection of the biliary tree. They are essentially an infectious disease of the biliary tree, and as such, their only major risk factor is mechanical bile stasis because of obstruction or, in some cases, a duodenal diverticula. In contrast, the formation of cholesterol and black pigment stones depends on a physical-chemical problem (Table 68), that is, the presence of an excess of insoluble constituents of bile. Hence, the composition of these three types of gallstones differs. Cholesterol is the major constituent of cholesterol gallstones, which also contain small amounts of inorganic calcium salts and the calcium salt of bilirubin. Black pigment stones contain large amounts of calcium and bilirubin, whereas brown pigment stones are composed of calcium salts of lipids degraded by bacteria, such as fatty acid soaps, as well as smaller amounts of bilirubin and cholesterol.
The type of stone can often be identified visually. Cholesterol stones may be solitary or they may oc-
cur as several stones of similar size, suggesting that stone formation occurred at a single instant. Numerous tiny stones may not be individually identified on ultrasound. Black pigment stones are amorphous, but may be faceted, a finding consistent with their high content of polymerised bilirubin pigment. Brown pigment stones are frequently laminated and occur on a nidus of infection, which may be either a cholesterol or black pigment stone in the Western Hemisphere or frequently a parasite in the Eastern Hemisphere.