**2. Pathogenesis of gallstones**

Gallstones are classified into cholesterol stone and pigment stone. Pathogenesis of cholesterol gallstone formation is considered to consist of three elements. First is biliary stasis, second is nucleation, and third is lithogenic bile (**Figure 1**) [1]. A cause of lithogenic bile has derived from cholesterol supersaturation. Aggregation of cholesterol-phospholipid vesicles is important to nucleation and formation of cholesterol-crystal. Biliary stasis in the gallbladder has been another factor associated with an increased incidence of cholelithiasis [2]. Pigmented stones are classified as either brown or black stones. Pathogenesis of pigmented stone is considered a result of infection [3].
