Comparative Follow-Up of Patients with Acute and Obtuse Infundibulum-Pelvic Angle Submitted to Extracorporeal Shockwave Lithotripsy for Lower Caliceal Stones: Preliminary Report and Proposed Study Design

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Abstract
Nowadays, there is a consensus that the poor success rate of extracorporeal shockwave lithotripsy (SWL) is in the treatment of lower caliceal stones. The gravity-dependent position of the lower-pole calices is postulated to be the main factor hindering the spontaneous passage of stone debris that results from SWL. Nevertheless, we proposed that there are some particular features of the inferior-pole collecting system anatomy that could contribute to fragment retention. We studied the influence of the lower infundibulum-pelvic angle on fragment retention, considering 74 patients submitted to SWL for the treatment of lower-pole nephrolithiasis in a Lithostar Plus machine. At a mean follow-up of 9 months, 75% of the patients presenting an angle of greater than 90 degrees between the lower infundibulum where the stone was located and the renal pelvis became stone-free within 3 months. On the other hand, only 23% of the patients presenting an angle smaller than 90 degrees between the lower infundibulum where the stone was located and the renal pelvis became stone-free during the follow-up. Determination of the angle between the renal pelvis and the infundibulum of the inferior pole calix where the stone is located is very important, because the angle will differ in the same kidney, depending on stone location. Although preliminary and based on a small series of patients, our data suggest that an acute pelvic-lower pole infundibular angle hinders the spontaneous discharge of fragments after SWL. Also, use of the proposed technique of pelvic-lower pole infundibular angle measurement will be important for unifying angle evaluation by other investigators.