Comment

Abstract

The pathogenesis and composition of biliary stones vary in different parts of the biliary system. However, classification based simply on their location is not helpful because stones can migrate. Because of a difference in chemical compositions, biliary stones may have different colors. Pure cholesterol stones are pearly or yellowish in color and are found mostly in the gallbladder. They form as a result of cholesterol supersaturation and crystallization. Recent studies demonstrated the presence of bacterial DNA in the center of cholesterol stones and suggested that bacteria may play a role in their formation. Brown and black pigment ductal stones are mixed stones containing calcium bilirubinate and a varying amount of cholesterol. Brown pigment stones are found typically in the common bile duct of patients with oriental cholangitis but may account for recurrent bile duct stones after sphincterotomy. They form as a result of bacterial infection, mostly by large bowel flora, and subsequent biofilm formation. The majority of brown stones have a mixed infection containing both gram-negative and gram-positive bacteria. Recent studies showed that anaerobic bacteria are present in a substantial number of biliary stones and suggested that they too may play a role in ductal stone formation.