Brown pigment gallstones are formed due to:

Characteristics of different types of gallstones and major risk factors for cholesterol gallstones Cholesterol stones Brown pigment stone Black pigment stone Main composition Cholesterol 50% bilirubin >50% bilirubin Colour Yellow-grey Brown Dark Brown-black Aetiology Cholesterol supersaturation Increased deconjugation of bilirubin glucuronides Increased biliary bilirubin load Ref: J Gastrointestin Liver Dis March 2011 Vol. 20 No 1, 9-11.