Is stone radiodensity a useful parameter for predicting outcome of extracorporeal shockwave lithotripsy for stones < or = 2 cm?

PURPOSE Several factors determine the success of extracorporeal shockwave lithotripsy (SWL) for kidney stones: stone size, stone location within the collecting system, stone type, and the SWL machine used. It has been suggested that stone radiodensity, as determined either by plain radiography or computed tomography attenuation values, may be an independent predictor of SWL success. We examined the outcome of SWL for solitary stones less than or equal to 2 cm located within the renal pelvis, based on their radiodensity. MATERIAL AND METHODS 211 patients with solitary renal pelvic stones measuring less than or equal to 2 cm were treated on a Dornier Doli 50 lithotriptor under general anesthesia. The radiodensity of the stone was determined to be either less than, equal to, or greater than the radiodensity of the ipsilateral 12th rib. Stone-free rates (SFR) were determined at 3 months by kidney, ureters and bladder (KUB) plain X-rays. Patients requiring re-treatment or auxiliary procedures were considered failures of SWL. RESULTS Follow-up SFR information was available in all 211 patients. Stone composition was available in 158 (75%) treated patients, but no correlation was found between stone radiodensity and stone composition. For stones < or = 10 mm within the renal pelvis, the SFRs were similar (71 to 74% regardless of stone radiodensity). For stones between 11 and 20 mm, the SFR was 60% if the stone had a radiodensity > 12th rib compared to a SFR of 71% if the stone radiodensity was < or = 12th rib. However, these differences in SFRs were not statistically significant. CONCLUSIONS On the Doli machine, stone radiodensity alone does not predict lithotripsy treatment outcome for stones < or = 1 cm within the renal pelvis. This parameter is probably only useful as the stone size becomes larger than 1 cm, and should be used in conjunction with other stone parameters to select appropriate therapy.