Clearance of lower-pole stones following shock wave lithotripsy: Effect ofthe infundibulopelvic angle

Objective: To assess the effect of anatomic factors, especially the angle o f the lower-pole infundibulum, on stone clearance following shock wave lith otripsy (SWL) in order to determine selection criteria for percutaneous nep hrolithotomy. Methods: We retrospectively analyzed 116 patients with single lower-pole stones measuring 11-20mm treated with SWL. Intravenous urograms were reviewed to measure the infundibulopelvic angle, the angle of the inf undibulum to the vertical, and the anatomy of lower-pole calyces. Results: The overall stone-free rate was 52%. Factors most closely associated with a stone-free status were obtuse infundibulopelvic angle, lack of calyceal di stortion, and a large infundibular diameter. The infundibulopelvic angle wa s 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 a fter SWL. Conclusion: 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 ro le in eventual stone clearance and should be taken into account before choo sing a mode of treatment.