Role of non contrast helical CT in predicting the outcome of extracorporeal shock wave lithotripsy

ABSTRACT

To evaluate the usefulness of urinary calculi attenuation values from non-contrast computed tomography [NCCT] in predicting the outcome of treatment by extracorporeal shock wave lithotripsy [ESWL]. Between 1[st] January 2007 and 30[th] June 2008, we evaluated 178 patients undergoing ESWL for solitary urinary calculi. All patients had NCCT at 120 Kv and 240mA on a helical CT scanner. During each ESWL session 3000 shock waves were given to a maximum of 3.0Kv.A final plain X-ray of the kidney, ureters and bladder was taken 12 weeks after the last ESWL session. Fragments of calculi retrieved were analysed and the resuls assessed by comparing the mean density in Hounsfield Units with the number of ESWL sessions and clearance. In all, 92 [79%] patients had complete clearance of stones and 24 [21%] had CIRF. There was alinear relationship between the calculus density and the number of ESWL sessions required. Of patients with calculi of >/= 750HU, 52 [84%] needed three or fewer ESWL sessions and 57[92%] had complete clearance. Of patints with calculi of>750HU, 40 [74%] required three or more ESWL sessions, and 32[60%] had complete clearance. The best outcome was in patients with calculus diameters of<1.1 cm and mean densities of patients with calculus densities of >750HU and diameter of > 1.1cm; 18[75%] needed three or more ESWL sessions and the clearance rate was only 50%. The calculus density was a stronger predictor of outcome than size alone The HU measurement of urinary calculi [stone density] on pretreatment non contrast CT predicts the stone free rates after ESWL. This might help in planning alternative treatment in patients with a probable poor outcome, and to increase the efficiency of ESWL, thus decreasing the cost of treatment