Stone Attenuation and Skin-to-Stone Distance on Computed Tomography Predicts for Stone Fragmentation by Shock Wave Lithotripsy


      To determine whether stone attenuation and the skin-to-stone distance (SSD) can predict for stone fragmentation by SWL independently. Identifying the factors predictive of shock wave lithotripsy (SWL) outcome would help streamline the care of patients with stones.


      A retrospective review was performed of 111 patients undergoing initial SWL for a solitary, 5-20 mm, renal calculus. Stone size, location, attenuation value, and SSD were determined on pretreatment noncontrast computed tomography. The outcome was categorized as stone free, complete fragmentation <5 mm, and incomplete fragmentation ≥5 mm or unchanged at 2 weeks on kidney/ureter/bladder radiography.


      After SWL, 44 (40%) were stone free, 27 (24%) had complete fragmentation, and 40 (36%) of 111 patients had incomplete fragmentation. The stone attenuation of the successfully treated patients (stone free and complete fragmentation groups) was 837 ± 277 Hounsfield units (HU) vs 1092 ± 254 HU for those with treatment failure (incomplete fragmentation; P < .01). The mean SSD also differed: 9.6 cm ± 2.0 vs 11.1 cm ± 2.5 for the successful treatment group vs the treatment failure group, respectively (P = .01). On multivariate analysis, the factors that independently predicted the outcome were stone attenuation, SSD, and stone composition. When patients were stratified into 4 risk groups (stone <900 HU and SSD <9.0 cm, stone <900 HU and SSD ≥9.0 cm, stone ≥900 HU and SSD <9.0 cm, and stone ≥900 HU and SSD ≥9.0 cm), the SWL success rate was 91%, 79%, 58%, and 41%, respectively (odds ratio 7.1, 95% confidence interval 1.6-32 for <900 HU and SSD <9.0 cm group vs other 3 risk groups; P = .01).


      The results of our study have shown that a stone attenuation of <900 HU, SSD of <9 cm, and stone composition predict for SWL success, independent of stone size, location, and body mass index. These factors will be considered important in the prospective design of a SWL treatment nomogram at our center.
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        • Park H.
        • Park M.
        • Park T.
        Two-year experience with ureteral stones: Extracorporeal shock wave lithotripsy vs ureteroscopic manipulation.
        J Endourol. 1998; 12: 501-504
        • Abe T.
        • Akakura K.
        • Kawaguchi M.
        • et al.
        Outcomes of shockwave lithotripsy for upper urinary-tract stones: A large-scale study at a single institution.
        J Endourol. 2005; 19: 768-773
        • Coz F.
        • Orvieto M.
        • Bustos M.
        • et al.
        Extracorporeal shock wave lithotripsy of 2000 urinary calculi with the Modulith SL-20: Success and failure according to size and location of stones.
        J Endourol. 2000; 14: 239-246
        • White W.
        • Klein F.
        Five-year clinical experience with the Dornier Delta lithotriptor.
        Urology. 2006; 68: 28-32
        • Albala D.M.
        • Assimos D.G.
        • Clayman R.V.
        Lower pole I: A prospective randomized trial of extracorporeal shock wave lithotripsy and percutaneous nephrostolithotomy for lower pole nephrolithiasis: Initial results.
        J Urol. 2001; 166: 2072-2080
        • Pace K.T.
        • Ghiculete D.
        • Harju M.
        • et al.
        Shock wave lithotripsy at 60 or 120 shocks per minute: A randomized, double-blind trial.
        J Urol. 2005; 174: 595-599
        • Saw K.C.
        • McAteer J.A.
        • Fineberg N.S.
        • et al.
        Calcium stone fragility is predicted by helical CT attenuation values.
        J Endourol. 2000; 14: 471-474
        • Joseph P.
        • Mandel A.K.
        • Singh S.K.
        • et al.
        Computerized tomography attenuation value of renal calculus: Can it predict successful fragmentation of the calculus by extracorporeal shock wave lithotripsy? A preliminary study.
        J Urol. 2002; 167: 1968-1971
        • Pareek G.
        • Armmenakas N.A.
        • Fracchia J.A.
        Hounsfield units on computerized tomography predict stone-free rates after extracorporeal shock wave lithotripsy.
        J Urol. 2003; 169: 1679-1681
        • Pareek G.
        • Armenakas N.A.
        • Panagopoulos G.
        • et al.
        Extracorporeal shock wave lithotripsy success based on body mass index and Hounsfield units.
        Urology. 2005; 65: 33-36
        • Gupta N.P.
        • Ansari M.S.
        • Kesarvani P.
        • et al.
        Role of computed tomography with no contrast medium enhancement in predicting the outcome of extracorporeal shock wave lithotripsy for urinary calculi.
        BJU Int. 2005; 95: 1285-1288
        • Pareek G.
        • Hedican S.P.
        • Lee Jr, F.T.
        • et al.
        Shock wave lithotripsy success determined by skin-to-stone distance on computed tomography.
        Urology. 2005; 66: 941-944
        • Favela R.
        • Gutierrez J.
        • Bustos J.
        • et al.
        CT attenuation value and shockwave fragmentation.
        J Endourol. 2005; 19: 5-10
        • Perks A.
        • Gotto G.
        • Teichman J.M.H.
        Shock wave lithotripsy correlates with stone density on preoperative computerized tomography.
        J Urol. 2007; 178: 912-915
        • Williams Jr, J.C.
        • Kim S.C.
        • Zarse C.A.
        • et al.
        Progress in the use of helical CT for imaging urinary calculi.
        J Endourol. 2004; 18: 937-941
        • Williams Jr, J.C.
        • Saw K.C.
        • Monga A.G.
        Correction of helical CT attenuation values with wide beam collimation.
        Acad Radiol. 2001; 8: 478-483
        • Denstedt J.D.
        • Clayman R.V.
        • Preminger G.M.
        Efficacy quotient as a means of comparing lithotriptors.
        J Endourol Suppl. 1990; 4: 100
        • Yilmaz S.
        • Sindel T.
        • Arslan G.
        • et al.
        Renal colic: Comparison of spiral CT, US and IVU in the detection of ureteral calculi.
        Eur Radiol. 1998; 8: 212-217
        • Dretler S.P.
        • Spencer B.A.
        CT and stone fragility.
        J Endourol. 2001; 15: 31-36
        • Sheir K.Z.
        • Mansour O.
        • Madbouly K.
        • et al.
        Determination of the chemical composition of urinary calculi by noncontrast spiral computerized tomography.
        Urol Res. 2005; 33: 99-104
        • Saw K.C.
        • Mcateer J.A.
        • Monga A.G.
        • et al.
        Of urinary calculi: Effect of stone composition, stone size, and scan collimation.
        AJR Am J Roentgenol. 2000; 175: 329-332
        • Mostafavi M.R.
        • Ernst R.D.
        • Saltzman B.
        Accurate determination of chemical composition of urinary calculi by spiral computerized tomography.
        J Urol. 1998; 159: 673-675
        • Motley G.
        • Dalrymple N.
        • Keesling C.
        • et al.
        Hounsfield unit density in the determination of urinary stone composition.
        Urology. 2001; 58: 170-173
        • Nakada S.Y.
        • Hoff D.G.
        • Attai S.
        • et al.
        Determination of stone composition by noncontrast spiral computed tomography in the clinical setting.
        Urology. 2000; 55: 816-819