Ureteral stones: SWL treatment

Abstract

When stone removal is indicated SWL (Shock Wave Lithotripsy) and ureteroscopy (URS) are the two most commonly offered interventional procedures and they are both acceptable as first-line treatment. The choice of the procedure depends on several factors, including local experience, patient preference, available equipment, and associated costs. The meta-analysis by the EAU/AUA Guideline Panel in 2007 analysed SWL stone-free results for three locations in the ureter (proximal, mid, distal) and reported an overall stone-free rate for proximal ureteral stones of 82%, with no difference in stone-free rate from URS results. However, for stones < 10 mm SWL, at 90%, had a higher stone-free rate than URS and even for mid and distal ureter it reached a stone-free rate of 84% and 86% respectively. It does appear that SWL may be more effective in the paediatric subset than in the overall population, particularly in the mid and lower ureter with a stone free rate of 82% and 80% respectively. In fact, children appear to pass stone fragments after SWL more readily than adults. SWL is a safe method to treat ureteral stones and serious complications occur very rarely when proper indications are followed. A few published studies addressed the role of SWL in acute renal colic. The available data suggest that is a safe procedure, with an overall success of 70-80% and a need for further intervention in 2-20%. In choosing the optimal therapy for an individual patient, several factors that might affect the outcome should be considered to identify the best candidate for SWL. A superior success rate for proximal ureteral stones was reported in the EAU/AUA meta-analysis but stone size over 10 mm appears negatively correlated with the stone-free rate. About composition, calcium oxalate monohydrate, brushite, cystine and matrix are unfavourable compositions for SWL. Finally, impacted stones are often more resistant to fragmentation. Whether hydronephrosis affects the outcome of SWL remains controversial. A body mass index of over 30 has been found to be an independent factor in predicting failure of SWL treatment in ureteral stones. A number of treatment strategies have been proposed to increase SWL efficacy: a promising suggestion to improve SWL outcome is to reduce the shock wave rate. There have also been attempts to improve shock wave efficiency of stone fragmentation with new shock wave lithotriptor devices. But although these innovation are promising, no advantage in stone-free rate or retreatment rate have yet been proven. Acoustic coupling is a key factor affecting the efficacy of shock wave lithotripsy. An accurate pre-treatment assessment of stone burden and composition with unenhanced CT scan provides useful information to discern which treatment strategy should be favoured and may reduce SWL failure. The real cost for SWL and URS varies considerably from one centre to another, as a result of different internal organisations and also due to the principles of reimbursement from the health care system.

Conclusions: SWL is the first treatment choice for stones smaller than 1 cm in the proximal ureter With a lower grade of invasiveness and the possibility to complete the treatment with only analgesics and sedation on an outpatient basis, SWL still appears an excellent alternative for removing ureteral stones and these properties compensate for the higher need for repeated treatments. An accurate pre-treatment assessment of stone and clinical factors to select the best candidates for SWL could improve the stone-free rate and reduce retreatments.