There are two types of gallstones
- Cholesterol stones
- Pigment stones
In the western world 80% of the gallstones are cholesterol stones. These are pale yellow in color. Usually formed due to crystallization of cholesterol.
Bile pigment stones
These are very different from cholesterol gallstones and pathogenesis is also different. Pigmented stones are further categorized into 2 subtypes,
Black pigment stones
Black pigment stones composed of calcium bilirubinate and a network of mucin glycoproteins. These substances precipitate in conjugation with calcium carbonate and/or calcium phosphate. These stones range from very dark brown to black. Pigment stones are seen in 40% - 60% of patients with hemolytic anemias. Pigment stones can occur even without hemolysis. .
Brown pigment stones
These stones have alternative tan and brown layers and muddy in appearance. Brown stones are usually composed of calcium salts and fatty acids.