The impact of radiological anatomy in clearance of lower calyceal stones after shock wave lithotripsy in paediatric patients.

Abstract

To determine the factors affecting stone clearance after extracorporeal shock wave lithotripsy (ESWL) in children with lower calyceal stones. Lower pole stone clearance was reviewed in 34 patients aged between 2 and 16 years (23 boys and 11 girls) treated with ESWL between 1989 and 2001 in our clinic. Renal anatomy was determined on standard intravenous urograms. The lower infundibulopelvic angle (IPA) was measured by two different methods based either on measuring the angle between vertical pelvis axis and vertical axis of lower infundibulum or finding the angle between the ureteropelvic axis and vertical axis of lower infundibulum. The mean age of the patients was 12.1+/-4.16 (2-16) years. The mean stone burden was found as 96.93+/-87.13 mm(2) and the mean shock wave number per session and power as 2631.4+/-593.1 and 17.57+/-1.1 kV, respectively. The stone-free rate was 55.9%. Fifteen (44.1%) cases had residual fragments retained in lower calices after lithotripsy and are still followed. The stone clearance was found to be unrelated to stone burden and infundibulum width (p=0.44 and p=0.34, respectively). However, a significant difference was present between mean lower pole infundibular length (p=0.0032) and lower IPA measurements according to both methods between stone-free cases and others. The most remarkable factor that had a significant influence on stone clearance was an acutely oriented infundibulum defined according to IPA-ureteropelvic axis angle determination method (p=0.00001) followed by Sampaio's pelvic axis method (p=0.0001). Only 1 (5%) patient was stone-free under 40 degrees and 1 (6%) case with an angle of 45 degrees had residual fragments in the former method. Similarly none of the cases had residual fragments over 90 degrees for Sampaio's method and 90% of the stone-free cases had a more obtuse angle. Thus, we determined that a cut-off point of 40 degrees for the IPA-ureteropelvic axis method and 90 degrees for Sampaio's method was most useful to determine the clearance of lower pole fragments. The factors affecting stone clearance in paediatric patients are similar to adults.