Classification

Gallstones are quite common in modern populations, occurring in nearly 20 percent of autopsies. Though often asymptomatic, they can produce significant morbidity, leading to cholecystitis, cholangitis, biliary cirrhosis, and pancreatitis.

The chief constituents of gallstones are cholesterol, bilirubin, and calcium. Other components may include fatty acids, triglycerides, protein, and polysaccharides. Descriptively, there are four major types of gallstones: (1) pure cholesterol stones; (2) mixed stones composed of cholesterol, bilirubin, and calcium; (3) combined stones having a cholesterol center and laminated exterior of cholesterol, bilirubin, and calcium; and (4) black or brown pigmented stones composed of calcium bilirubinate.

The first three types comprise the vast majority of gallstones and may be grouped together as cholesterol-based stones, pathogenetically related to abnormal cholesterol and bile salt metabolism. Black pigmented stones are commonly associated with chronic hemolysis, particularly sickle-cell disease. Gallstones stones occur in 40 to 60 percent of patients with sickle-cell disease. Brown pigmented stones are associated with infection. These were historically more common in China and Japan, perhaps related to bile stasis and infection caused by Ascaris lumbricoides (roundworm) and Clonorchis sinensis.

Etiology and Epidemiology

Though incompletely understood, the three major factors in gallstone formation are abnormality in bile composition, biliary stasis, and gallbladder infection. These factors are interrelated, but current thinking ascribes the primary role to abnormal bile composition, related to cholesterol and bile acid metabolism. This in turn is affected by dietary, genetic, and hormonal factors.