Transient acoustic cavitation in gallstone fragmentation: a study of gallstones fragmented in vivo.

The mechanism of gallstone fragmentation by shock waves in vivo is uncertain. We used scanning electron microscopy to study 9 partially fragmented stones obtained from 6 patients who underwent lithotripsy and subsequently had surgery because of incomplete fragmentation. Surface characteristics of the stone were studied using scanning electron microscopy and compared to gallstones fragmented in degassed water in vitro and to control stones obtained from patients with uncomplicated cholelithiasis. Characteristic damage caused by transient acoustic cavitation was visible in all stones fragmented in vivo and in vitro as pits 10-100 microns diameter. In these pits, cholesterol crystals were fractured, and the symmetry of crystal boundaries was damaged. In areas of more severe damage, individual pits coalesced to form craters on the stone surface. High magnification of the pit walls revealed cracks, which in some instances radiated out onto the unpitted surface of the stone. We conclude that transient acoustic cavitation plays a role in gallstone fragmentation in vivo through the mechanism of surface pitting and the formation of cracks that radiate outward from the surface pits. Measures to enhance cavitation may improve the results of gallstone lithotripsy.