Clearance of Lower-Pole Stones following Shock Wave Lithotripsy: Effect of the Infundibulopelvic Angle

To assess the effect of anatomic factors, especially the angle of the lower-pole infundibulum, on stone clearance following shock wave lithotripsy (SWL) in order to determine selection criteria for percutaneous nephrolithotomy.We retrospectively analyzed 116 patients with single lower-pole stones measuring 11-20 mm treated with SWL. Intravenous urograms were reviewed to measure the infundibulopelvic angle, the angle of the infundibulum to the vertical, and the anatomy of lower-pole calyces.The overall stone-free rate was 52%. Factors most closely associated with a stone-free status were obtuse infundibulopelvic angle, lack of calyceal distortion, and a large infundibular diameter. The infundibulopelvic angle was the only factor to attain significance in predicting stone-free status (p = 0.012). The size of the stone did not predict eventual stone-free status (p = 0.911), but larger stones were more likely to require intervention after SWL.For solitary lower-pole stones 11-20 mm in size, the angle of the lower-pole infundibulum as it relates to the pelvis plays a role in eventual stone clearance and should be taken into account before choosing a mode of treatment.