ORIGINAL ARTICLE Influence of the renal lower pole anatomy and mid-renal-zone classification in successful approach to the calices during flexible ureteroscopy Bruno Marroig 1 • Rodrigo Frota 1 • Marco A. Fortes 1 • Francisco J. Sampaio 1 • Luciano Alves Favorito 1 Received: 10 July 2015 / Accepted: 26 September 2015 / Published online: 6 October 2015 Ó Springer-Verlag France 2015 Abstract Purpuse The aim of this paper is to analyze if the anat- omy type of the collector system (CS) limits the accessi- bility of flexible ureteroscopy (FUR) in the lower pole. Methods We analyzed the pyelographies of 51 patients submitted to FUR and divided the CS into four groups: A1—kidney midzone (KM) drained by minor calices (Mc) that are dependent on the superior or on the inferior cal- iceal groups; A2—KM drained by crossed calices; B1— KM drained by a major caliceal group independent both of the superior and inferior groups, and B2—KM drained by Mc entering directly into the renal pelvis. We studied the number of calices, the angle between the lower infundibulum and renal pelvis, and the angle between the lower infundibulum and the inferior Mc. With the use of a flexible ureteroscope, the access attempt was made to all of lower pole calices. Averages were statistically compared using the ANOVA and Unpaired T test (p \ 0.05). Results We found 14 kidneys of A1 (27.45 %); 4 of A2 (7.84 %); 17 of B1 (33.33 %); and 16 of B2 (31.37 %). The LIP was [ 90° in 31 kidneys (60.78 %) and between 61° and 90° in 20 kidneys (39.22 %). We did not find angles smaller than 60°. The group A1 presented 48 Mc and the UF was able to access 42 (87.5 %); the group A2 had 11 Mc and the UF was able to access 7 (63.64 %); the group B1 had 48 Mc and the UF was able to access 41 (85.42 %) and in group B2 we observed 41 Mc and the UF could access 35 (85.36 %). There was no statistical difference in the accessibility between the groups (p = 0.2610). Conclusions Collecting system with kidney midzone drained by crossed calices presented the lower accessibility rate during FUR. Keywords Flexible ureteroscopy Á Kidney anatomy Á Lower pole anatomy Introduction The flexible ureteroscopy (FUR) is a method widely used for the treatment of lower pole renal stones [5, 7]. The best results with the FUR are with the stones less than 20 mm [3]. However, the success rate in the treatment of the kidney stones for the lower pole is directly related to fac- tors of this anatomical region [2, 6, 19]. The spatial anatomy of calices in lower pole is described to influence the success rate of FUR [4, 8]. The measure of angles between the lower infundibulum and the minor calices, the length and the width of the infundibulum, and the presence of perpendicular calices are the anatomical factors of greatest interest to the success of FUR [4, 8, 11, 16]. Patients with unfavorable anatomical factors have lower rates of success in FUR [4, 8]. Recently, we studied the lower pole anatomy by the mid-renal-zone classification of collecting system applied to Flexible ureteroscopy in 170 human kidney endocasts and show that this classification was predictive for lower pole ureteroscopy difficulties [12]. Studies that correlate the collecting system classification with the success rate for accessing the lower pole calices during FUR are unknown. The aim of this paper is to analyze if the type of col- lecting system anatomy limits the accessibility of the & Luciano Alves Favorito lufavorito@yahoo.com.br 1 Urogenital Research Unit, State University of Rio de Janeiro, 104/201 Tijuca, Rio de Janeiro CEP:20271-320, Brazil 123 Surg Radiol Anat (2016) 38:293–297 DOI 10.1007/s00276-015-1562-0