Black and brown pigment gallstones are morphologically, compositionally, and clinically distinct. Black stones form primarily in the gallbladder in sterile bile and are associated with advanced age, chronic hemolysis, alcoholism, cirrhosis, pancreatitis, and total parenteral nutrition. Brown stones form not only within the gallbladder but also within the intrahepatic and extrahepatic ducts; they are uniformly infected with enteric bacteria and are usually associated with ascending cholangitis. Brown stones are related to juxtapapillary duodenal diverticula and are the predominant type of de novo common bile duct stones. Cholecystectomy is usually curative in black pigment stone disease, whereas stones often recur after cholecystectomy for brown stone disease. The pathogenesis of black stones is probably related to nonbacterial, nonenzymatic hydrolysis of bilirubin conjugates. At the pH of bile, this results in two monohydrogenated bilirubin anions that precipitate with calcium ions. Bilirubin monoconjugates that are increased in several conditions, such as Gilbert’s syndrome and chronic hemolysis, may play a pivotal role in black stone formation as a source of unconjugated monohydrogenated bilirubin and as a possible co-precipitant with calcium. The precipitation of calcium carbonate and phosphate is influenced by local gallbladder factors. Brown pigment stones are formed in bile infected with enteric bacteria that elaborate hydrolytic enzymes: beta-glucuronidase, phospholipase A, and conjugated bile acid hydrolase. The resulting anions of bilirubin and fatty acids form insoluble calcium salts. We used nb/nb mice with a chronic hemolytic anemia as a model of hemolysis-induced black stone disease. The presence of 40% bilirubin monoconjugates in mouse gallstones indicated the importance of this moiety in the pathogenesis of black stones. Other data obtained by marrow transplantation experiments in mice revealed the relative importance of genotype versus the hemolytic anemia on determinants such as biliary bile acid composition and mucin secretory glands in the mouse gallbladder neck. Additional physical chemical studies of the interaction of unconjugated bilirubin in model bile solutions will be helpful in further delineating the pathogenesis of both black and brown pigment gallstones.

Source: http://www.ncbi.nlm.nih.gov/pubmed/2022417