Pelvicalyceal anatomy on the accessibility of reusable flexible ureteroscopy to lower pole calyx during retrograde intrarenal surgery

Objective This study aimed to evaluate the pelvicalyceal anatomy on accessibility of reusable flexible ureteroscopy (fURS) to the lower pole calyx during retrograde intrarenal surgery (RIRS). Methods Here, 854 patients with ureteral or kidney stones with access to a renal collecting system using reusable fURS were classified into either the accessible group, in whom the deepest lower pole calyces could be touched; and the inaccessible group, in whom the deepest lower calyces could not be touched. We measured the infundibulopelvic angle (IPA), infundibular width (IW), infundibular length (IL), and calyceal pelvic height (CPH) using retrograde pyelograms and performed intergroup comparisons. Results The median IPA, IW, IL, and CPH in the accessible and inaccessible group were 60.5° and 45.6° ( p < 0.001), 10.8 and 9.4 mm ( p < 0.001), 33.2 and 36.4 mm ( p < 0.001), and 25.9 and 30.9 mm ( p < 0.001), respectively. IPA (OR 0.963, 95% CI 0.952–0.974, p < 0.001) and IW (OR 0.519, 95% CI 0.331–0.816, p = 0.004) were significant risk factors of renal pelvicalyceal anatomy related to the accessibility of the lower pole calyces. The cut‐off value for IPA and IW was 45.8°( p < 0.001) and 7.8 mm ( p < 0.001), respectively. Conclusions IPA < 45.8° and IW <7.8 mm were negative predictors to access the lower pole calyces when using reusable fURS during RIRS.