Value of Hounsfield unit on CT in prediction of stone-free rate of upper urinary calculi after extracorporeal shockwave lithotripsy

Abstract

To study the value of Hounsfield unit (HU) on CT in prediction of stone-free rate of upper urinary calculi after extracorporeal shockwave lithotripsy (ESWL). Fifty-two patients suffering from solitary stone in the upper urinary tract 0.5 - 1.5 cm in size, 34 males and 18 females, aged 15 - 77, underwent non-contrast helical computerized tomography (NCHCT), and then ESWL. One day, 2 weeks, 4 weeks, and 3 months after the ESWL the patients underwent kidney, ureter, and bladder examination and B mode ultrasonography. The patients with the residual fragments less than 3 mm in size were categorized into the stone-free group. The relationship among the HU, number of shock wave, and the characteristics of the patients were analyzed. Thirty-six of the 52 patients were categorized into the stone-free group (69.2%) and 16 of the 52 were categorized into the residual stone group (30.8%). The CT value of the stone-free group was 579.65 +/- 194.65 HU, significantly lower than that of the residual stone group (1032.18 +/- 270.49 HU, t = 6.842, P < 0.01). The number of shock wave of the stone-free group was 1526.67 +/- 723.01, significantly lower than that of the residual stone group (2612.50 +/- 518.81, t = 5.407, P < 0.01). The OR values for the HU and number of shock wave were 0.993 (95% CI: 0.988 - 0.998) and 0.998 (95% CI: 0.997 - 1.000). The HU value on pretreatment NCHCT of the upper urinary tract stones can be used to predict the stone-free rate after ESWL. ESWL is not indicated to the patients of upper urinary tract stones with high values of HU.