Hounsfield Units on Computerized Tomography Predict Stone-Free Rates After Extracorporeal Shock Wave Lithotripsy

Abstract

Purpose: Studies suggest that HU values on noncontrast computerized tomography may predict the ability to fragment urinary calculi. We determined whether the HUs of in vivo urinary stones could be used to predict the stone-free rates after extracorporeal shock wave lithotripsy. Materials and Methods: We evaluated 50 patients who underwent extracorporeal shock wave lithotripsy for 5 to 10 mm. upper urinary tract stones. Chemical analyses and HU calculations were performed for each stone and posttreatment radiographic assessment categorized patients into a stone-free or a residual stone group. Statistical analysis was performed using the Student t test to compare mean HU values in the 2 groups. Results: Of the patients 32 (64%) were stone-free and 18 (36%) had residual stones. Mean values ± SEM for the stone-free and residual stone groups were significantly different (551.20 ± 46.66 versus 926.20 ± 51.42 HU, p <0.0001). A total of 30 calculi (60%) were located in the ureter, including 21 in the stone-free group and 9 in the residual stone group with a mean value of 505.10 ± 46.66 and 888.70 ± 102.00 HU, respectively, which was significantly different (p =0.0005). A total of 20 calculi (40%) were located in the kidney, including 11 in the stone-free group and 9 in the residual stone group with a mean value of 558.40 ± 62.38 and 905.10 ± 61.49 HU, respectively, which was significantly different (p =0.001). Conclusions: These findings suggest that HU measurement of urinary calculi on pretreatment noncontrast computerized tomography may predict the stone-free rate. This information may be beneficial for selecting the preferred treatment option for patients with urinary calculi.