Microstructure of gallstones.

Electron microprobe analysis, x-ray diffraction, and infrared spectroscopy have been used to investigate the nature and arrangement of materials present in gallstones. Calcium phosphate and carbonate deposits present centrally in many stones were mixed with a pigmented phase containing copper and protein. In several stones, the central calcium deposits were surrounded by discrete adjacent layers of calcium bilirubinate and cholesterol. The calcium bilirubinate layer was distinguished from other pigmented layers by its higher protein content and increased iron/copper ratio. This sequence of calcium salt and cholesterol deposition occurred in the outer layers of some stones. The phase relationships shown by the present study are consistent with a biphasic mechanism of stone growth in which calcium salts and lipid were alternately deposited. Calcium salt precipitation has been inferred to initiate the sequence as calcium salts were found at the stone centers. The layer sequence has been discussed in terms of some possible effects of damage to the gallbladder wall caused by the calcium salt deposits.