Gallstones : Classification

Comments:
Classification of Gallstones: Gallstones are chiefly composed of cholesterol, bilirubin, calcium salts, and smaller quantities of other constituents. Based on the presence and amount of cholesterol, they are divided into:

CHOLESTEROL STONES (right panel): They arise almost exclusively in the gallbladder. They contain variable amounts of cholesterol. About 10% are pure cholesterol stones (i.e. composed of 100% cholesterol monohydrate). The remainder are MIXED STONES and contain at least 50% cholesterol monohydrate admixed with bilirubin calcium salts and small amounts of calcium carbonate and phosphate. They are the most common subtype in the Western countries.
PIGMENT GALLSTONES (left panel): They may be black or brown in color. They are composed predominantly of calcium salts of unconjugated bilirubin and have less than 30% cholesterol. They are primarily seen in the setting of bacterial infections or parasitic infestations of the biliary tree as well as in patients with chronic hemolytic conditions.
RARE SUBTYPES: Composed of calcium carbonate or calcium salts of fatty acids (stearate, palmitate).