Microstructural analysis of bile: Relevance to cholesterol gallstone pathogenesis

The study of physical-chemical factors and pathways leading to cholesterol crystallization in bile has important clinical relevance. The major processes in cholesterol gallstone formation can be subdivided into nucleation, formation and precipitation of solid crystals (crystallization), crystal growth, crystal agglomeration and stone growth. A clear understanding of the microstructural events occurring during the earliest stages of these processes in bile is crucial for the identification of factors possibly delaying or preventing precipitation of cholesterol crystals and, therefore, gallstone formation in bile. Detection and characterization of microstructures in native and model biles can be achieved by both direct and indirect techniques. Direct imaging techniques provide more readily interpretable information, but sample preparation problems, particularly for electron microscopy, are a source of artifacts. Moreover, microscopic techniques provide only qualitative data without the possibility to quantitate or to analyse the composition of microstructures. Several indirect techniques have been used to obtain additional microstructural information about nucleating bile. These techniques have the disadvantage of often being model dependent in addition to constraints specific for each method. The systematic, judicious use of a combination of complementary direct and indirect techniques have led to a comprehensive understanding of the various microstructural processes and interactions occurring during bile secretion, flow in the biliary tract and storage in the gallbladder. This forms the basis for our current understanding of cholesterol nucleation, crystallization and gallstone formation.