Correlation analysis between measurement methods of kidney stone burden and operation time or result of flexible ureteroscopic lithotripsy / 中华泌尿外科杂志

ABSTRACT

Objective:To evaluate the best parameter of predicting the operation time and clearance of flexible ureteroscopic lithotripsy through comparing correlations between three stone burden parameters (diameter, area, volume) and the operation time or clearance retrospectively.Methods:Clinical data and CT images of 70 patients who performed flexible ureteroscopic lithotripsy because of single kidney stone in our center from January 2018 to December 2019 were retrospectively reviewed. There were 46 males and 24 females; their age was (47±12) years old. Stones were located on the left side in 28 cases and right side in 42 cases; 32 cases in the renal pelvis , 29 cases in the lower calyx, 6 cases in the middle calyx and 3 cases in the upper calyx. The free software ITK-SNAP 3.6.0 to segment kidney stones in 3D models with the CT image was used. The stone volume was calculated automatically after the segment. The largest section of the stone on the CT coronal plane was selected to measure the maximum length (D) and width (d) of the stone, the maximum diameter of the stone was D, and the stone area was calculated using the formula 0.25πDd. The patients were divided by the operation clearance into total clearance group and partial clearance group. The correlations between three stone burden parameters (volume, diameter, area) and operation time or clearance of the flexible ureteroscopic lithotripsy were compared. Simple linear regression model was also applied to compare three measurement methods. Then other factors which may affect the operation time was evaluated with the stepwise linear regression model, such as stone component and location.Results:The median operation time was 63(50, 84)min. Of 70 cases, 47 cases were in the stone-free group, with stone volume 633(248, 1 087)mm 3, maximum diameter 15(10, 19)mm, and area 82(49, 186)mm 2. 23 cases were in the non stone-free group, with volume 696(408, 1 418)mm 3, maximum diameter 15(12, 20)mm, area 105(73, 201)mm 2. There was no difference between the two groups in volume, maximum diameter and area of stones (all P>0.05). The stone-free rate of the diameter >2 cm group was 55% (6/11), ≤2 cm group was 70% (41/59). There was no significant difference between the two groups. Correlation between stone volume and operation time is the best. The correlation coefficient of stone volume is 0.58, of stone diameter is 0.33, of stone area is 0.34. Coefficients of determination of the stone volume linear regression is the best, too. R square of stone volume is 0.36, of stone diameter is 0.17, of stone area is 0.22. Forward stepwise regression model shows stone volume is the most important parameter which correlate with operation time. None of stone volume, diameter or area has significant correlation with the clearance of stone. Conclusion:Stone volume is the best predictive parameter of the stone burden because it has the best correlation with the operation time of the flexible ureteroscopic lithotripsy of the single kidney stone.