Human gallstones: Specimen preparation and light microscopy
Several methods for removing gallstones from the human body are in use or under investigation. They range from noninvasive techniques (dissolving; ultrasound lithotripsy), through minor surgery (use of wire basket lithotriptor; laser lithotripsy), to major surgery. The choice of procedure seeks to accomplish removal of stones while minimizing the cutting of patient tissue, the post-treatment rehabilitation time, and the overall cost. The effectiveness of a given procedure will vary, depending on the size and number of stones present, and especially on their composition and microstructure. Attempts have therefore been made to correlate gallstone structure (from computerized tomography studies or magnetic resonance imaging with the least severe procedure needed to break up and remove the stone. Such empirical correlations can be facilitated by additional in vitro microstructural characterization of stones, which attempt to relate the in vivo observations to likely fracture paths and mechanisms. It is convenient to distinguish between three broad categories of gallstone. Cholesterol gallstones are associated with cholesterol supersaturation, when the level of cholesterol in bile exceeds the amount that the bile salts can keep in solution; they contain more than 25 wt% cholesterol and are relatively rare. Pigment gallstones contain less than 25 wt% cholesterol, and result from the precipitation and agglomeration of bilirubin and other inorganic salts. Mixed stones are the most common, and form the subject of our present investigations. Viewed in cross-section, they contain radiating crystals of cholesterol, together with concentric layers of apparently amorphous pigment. There are few literature references to the study of gallstone structure by light microscopy. We found only one reference to the microscopy of thin sections; others described low resolution reflected light studies of surfaces generated by dividing stones with a sudden impact delivered to a sharp knife. The drought of high resolution light micrographs even extends to pathology atlases.