Extracorporeal Shock Wave Lithotripsy:
a shocking blow for kidney stones
Extracorporeal Shock Wave Lithotripsy (ESWL) is the medical procedure by which acoustic shock waves, generated outside the body, are focused onto a kidney stone in the kidney or ureter causing the stone to fragment. The technique has been used in hospitals since 1980; currently more than 2000 lithotripters are in operation around the world and over five million treatments have been carried out. Approximately 70% of patients with stones can be treated with ESWL alone. A further 25% of patients receive ESWL in conjunction with some other procedure - avoiding the need for open surgery in 95% of cases of kidney stones.
Despite the success of ESWL there is no agreement in the community as to the mechanism by which the stone fails. Furthermore there is evidence that the shock wave leads to permanent damage to healthy tissue in the kidney. The significance of the injury is also debated.
The two major hypotheses for stone comminution are spallation and cavitation. Spallation refers to large tensile stress that the stone leading to stone failure probably by fatigue. Cavitation occurs when the tensile stress of the shock wave is strong enough to make fluid rip apart. The nature of the shock wave in lithotripsy leads to a dramatic growth of the bubble followed by a subsequently violent collapse. The collapse leads to an probably surface damaging microjets.
Boston University is part of a multi-disciplinary research effort to study
lithotripsy that involves: