PIGMENT GALLSTONES

Abstract

Pigment gallstones are dark brown-to-black stone, consisting of Ca salts of bilirubin, phosphate, carbonate and other anions, and can be separated into carbonate- and noncarbonate-containing groups. Pigment stones predominate in the rural Orient, in cirrhosis, and in elderly USA patients undergoing cholecystectomy. Clinical associations include bile duct obstruction, stasis and possibly hemolysis. Of pigment stones, 50% are radioopaque and account for 2/3 of all opaque stones. The concentrations of bile salts, phospholipids, cholesterol and total bilirubin in bile are similar to normal levels, but the concentration of unconjugated bilirubin is increased in the bile of some patients. Increased unconjugated bilirubin in bile may be caused by increased hydrolysis of excreted conjugated bilirubin. Unconjugated bilirubin is solubilized by bile salts, but the interaction is primarily nonmicellar. Ionized Ca and pH are important determinants of solubility. Sulfated glycoproteins, excreted in increased amounts in patients with cholelithiasis, may be the site of pigment stone precipitation, because these compounds bind Ca salts tightly. Escherichia coli is frequently cultured from pigment stones in Japan but not in the USA; thus, bacterial .beta.-glucuronidase may be important in stone formation in Japan but probably not in the West. Stasis leads to increased Ca secretion and to increases in the concentration of sparingly soluble compounds that may then precipitate. Incomplete emptying of the gallbladder may result in the same concentration process. Unsaturated fats and chronic vagal stimulation cause pigment stone formation in animals. Surgery is the only treatment for pigment lithiasis.