Abnormal gallbladder motor function, with delayed emptying and stasis apparently promote the formation of gallstones as well. Biliary sludge, a thick mucous material that forms in the most dependent portion of the gallbladder also promotes nucleation with the formation of stones. Pigmented stones, on the other hand, appear to form predominantly as a result of infection of the biliary tract with bacterial or parasitic agents. European people, of advancing age, female sex with a tendency to obesity, and a history of rapid weight loss are particularly prone to develop cholesterol stones. Pigmented stones, on the other hand, are far more often seen in Asian people, particularly with disorders of hemoglobin, resulting in an increase in hemolysis.
Gallstones are crystalline structures, formed by gradual accretion of components of bile.
Grossly, pure cholesterol stones are yellow, and on section, reveal a classic radiating pattern. Pigmented gallstones can be jet black. These are usually associated with a sterile gallbladder and are due to increased hemolysis. Brown pigmented stones are often associated with a repeated history infection. Stones are too hard to be subjected to routine histology and sections are not obtained.