Impact of stone density on the outcome of extracorporeal shock wave lithotripsy

Objectives This study aims to evaluate the attenuation of renal calculi measured by Hounsfield unit (HU) by noncontrast spiral computerized tomography (NCSCT) as a predictor of calculus fragmentation by extracorporeal shock wave lithotripsy (SWL). Background The outcome of extracorporeal SWL is measured in terms of stone fragmentation and clearance. Some authors have suggested that HU of renal calculi by NCSCT may predict stone-free rates after extracorporeal SWL. Patients and methods This prospective nonrandomized open study included 100 patients with renal stone up to 20 mm in size. Stone attenuation was measured by HU on NCSCT. Patients were grouped according to stone attenuation as group (1), less than 500 HU, (2), 500-1000 HU, and (3), greater than 1000 HU. Patients were treated subsequently with extracorporeal SWL. The outcome was categorized as stone free, clinically insignificant stone fragments, and residual fragments more than 3 mm. Results The rate of stone fragmentation was 100% (41 of 41 cases) in group 1, 95.7% (44 of 46) in group 2, and 0% (0 of 13) in group 3. A statistically significant association was found between SWL treatment outcome and stone density. When we correlated the absolute stone HU measured with the number of shock waves required for complete fragmentation, we found that the mean number of shock waves was 248 122 in group 1, 334 826 in group 2, and 726 077 in group 3 ( P Conclusion Stone attenuation measured by HU by NCSCT is a predictor of outcome of SWL and suspected number of shock waves required for fragmentation.