Pathophysiology: Gallstones are rocklike collections of material that form inside the gallbladder. Different types exist, and they are categorized by their primary composition; cholesterol stones are most common (75-80% in the United States) followed by pigment, then mixed stones. The stones form when there is an imbalance or change in the composition of bile.
Normally, bile acids, lecithin, and phospholipids help to maintain cholesterol solubility in bile. When bile becomes supersaturated with cholesterol, it crystallizes and forms a nidus for stone formation. Calcium and pigment also may be incorporated in the stone. Impaired gallbladder motility, biliary stasis, and bile content predispose people to the formation of gallstones.
Gallbladder sludge is crystallization within bile without stone formation. Sludge may be a step in the formation of stones, or it may occur independently. Five to fifteen percent of patients with acute cholecystitis present without stones (acalculous cholecystitis). This typically occurs in patients with prolonged illness, such as those with major trauma or with prolonged ICU stays.
Pigment stones, which comprise 15% of gallstones, are formed by the crystallization of calcium bilirubinate. Diseases that lead to increased destruction of red blood cells (hemolysis), abnormal metabolism of hemoglobin (cirrhosis), or infections (including parasitic) predispose people to pigment stones. Black stones and brown stones exist. Black stones are found in people with hemolytic disorders. Brown stones are found in the intrahepatic or extrahepatic duct. They are associated with infection in the gallbladder and commonly are found in people of Asian descent.
Gallstone differentiation is an important consideration in management; cholesterol stones are more likely to respond to nonsurgical management than are pigment or mixed stones.