How is pathogenesis of choledocholithiasis?

Gall stones pass to bile duct, or de novo form in duct. All of one type (cholesterol or pigment), cholesterol stones form only in gall bladder (not de novo) black pigment stones rarely merge to duct from gall bladder, majority are soft brown pigment stones (de novo from bacterial actions on phospholipids and bilirubin in bile). 15% of pt w/gall bladder stones also have bile duct stones, but pt w/ductal stones 95% also have gallstones