- Only 10% of gallstones are pure:
- Pure cholesterol stones: pale yellow, round/ovoid, granular surface, often single, crystalline core, radiolucent
- Pure calcium bilirubinate stones (pigment stones) are black oval, numerous; associated with cirrhosis and hemolytic disorders; when develop in setting of infection, brown rather than black and softer
- 80% of all gallstones are mixed with varying combinations of cholesterol, calcium bilirubinate, and calcium carbonate; usually multiple and laminated
- Some designate any stone with >70% cholesterol as a cholesterol stone and any with <30% cholesterol as a pigment stone
- Combined stones (10%) have either pure nucleus with a mixed shell or vice versa
- ~20% of stones have enough calcium to be radiopaque
- Bile salts and, to a lesser extent, lecithin (phospholipid) increase solubility of cholesterol in bile
- Lithogenesis promoted by excess of cholesterol relative to amount of bile salts, followed by nucleation precipitation and then growth of aggregates
- Biliary sludge with mucus and small crystals usually precedes stone formation
- Risk factors: female, age >40, obesity, multiple pregnancies; any drugs or hormones that increase cholesterol excretion or decrease bile salt levels promote stones