The Role of Unenhanced Spiral Computerized Tomography in Prediction of Successful Fragmentation of the Renal Calculus by Extracorporeal Shock Wave Lithotripsy

Abstract

Purpose: We evaluated the attenuation value of renal cal-culi on unenhanced axial computerized tomography (CT) as a predictor of calculus fragmentation by extracorporeal shock wave lithotripsy (ESWL). Patients and Methods: Fifty patients with renal calculi up to 20 mm were included in this prospective study. The calculus attenuation value was measured in Hounsfield units (HU) on unenhanced CT sections through the calculi. Patients were subsequently treated with ESWL. Results: Patients were grouped according to calculus attenuation value into 3 treatment groups, first those with stones less than 500 HU (20 patients), 2nd those with stones from 500 to 1,000 HU (14 patients) and 3rd those with stones greater than 1,000 HU (16 patients). Mean HU was calculated for each group. Of the 50 patients 41 (80%) underwent successful ESWL treatment. The stone clearance rate was 100% in group I (20 of 20 cases), 85.7% in group II (13 of 14), and 50% in group III (8 of 16). The clearance rate for stones with an attenuation value of greater than 1,000 HU was signifi-cantly lower than that for stones with a value of less than 1,000 HU (8 of 16 vs. 13 of 14 cases and 20 of 20 cases). Pa-tients in group III required a greater median number of shock waves for stone fragmentation than those in groups I and II. The mean attenuation value and number of shock waves required for calculus fragmentation correlated significantly. Conclusions: The CT attenuation value of renal calculi can help to differentiate stones that are likely to fragment easily on ESWL from those that would require a greater number of shock waves for fragmentation or may fail to fragment on ESWL.