Remarkable advances in instrument technology and increasing experience have caused significant changes in the treatment concepts of urinary stones. Regarding this issue, as a minimal invasive technique, flexible ureteroscopic stone disintegration has gained world-wide popularity with its successful and safe outcomes in the management renal stones up to 20 mm [1]. As an accessory tool in the successful performance of RIRS ureteral access sheaths (UAS) are being commonly used to provide an effective drainage and reduce the intrarenal pressure levels for a safe procedure. Apart from these advantages, published data so far have clearly demonstrated that the use of UAS could increase the visibility, reduce operative duration and allow multiple re-entries into the involved ureters [2]. Although its use seems to be associated with above mentioned critical advantages however, placement of UAS may not to be possible in around 22% of patients planned for this procedure. Additionally, failure to perform a ureteroscopic procedure due to a tight (difficult) ureter not allowing a passage in around 8–10% of the cases [3]. In case of such a difficulty during the procedure, placement of a ureteral stent and postponement of the procedure for a second stage has been accepted as the most rational approach. Related with this issue, presence of a ureteral stent in the involved reno-ureteral unit or placement of a stent prior to RIRS procedure have were found to dilate the ureter the and ease the procedure. However, as stent placement will require a second procedure for removal, this approach will not be rational and acceptable for the cases in clinical practice [3, 4]. Thus, it may be of value and helpful if endourologists could identify the cases who need presenting to overcome all these difficulties.

Taking the possible difficulty in the placement of an UAS during RIRS into account, physicians looked for some certain parameters to predict the likelihood of a smooth UAS insertion, and age, previous same-side procedures and presence of a preoperative stent were found to be independent factors on this aspect [3]. Presence of a ureteral stent in the involved reno-ureteral unit was reported to helpful and predictive [5]. Related with this issue again, although UAS placement was performed without any difficulty in patients with normal BMIs and in cases with a tent-shaped ureteral orifice [6], some other factors namely male gender and ipsilateral hydronephrosis were found to be associated with increased failure rates [7]. However, the published data so far on the predictive factors in the prediction of UAS passage are highly limited and contradictory. Studies evaluating the placement of UAS before RIRS procedures have pointed out that successful insertion of a UAS over the guidewire may not be possible in all cases with failure rates varying 10–22% [2,3,4]. As an advantage on this aspect the insertion of a ureteral stent before UAS placement was found to cause passive dilation and increase the success rates [3, 10]. According to one report however, UAS placement can also be unsuccessful in 7.7% of the cases even after ureteral stenting for a reasonable time period [11]. Taking the fact that routine ureteral stenting prior to UAS is not recommended by the European Association of Urology (EAU) guidelines [6] into account, it may be of great value to determine the risk factors in order to minimize the failure rates of UAS placement. In their original study, Alkhamees M et al. were able to show that none of the factors related to patient demographics or stone characteristics may be predictive enough for the failure of UAS placement [2]. On the other hand, as another diagnostic tool performed in all cases, radiologic evaluation of stone and anatomy related factors on this aspect may provide some valuable insights. Related with this issue, although non-contrast computed tomography (NCCT) has been used to identify the likelihood of ureteral stone passage [8,9,10], no study so far did focus on the possible role of radiologic parameters in the prediction of UAS passage, and to the best of our knowledge, this study is the first report using radiologic NCCT and KUB measurement parameters on this aspect.

In this present study we aimed to evaluate the possible predictive role of some demographic as well as radiological parameters identified in both KUB and NCCT images on the likelihood of UAS passage prior to RIRS procedures. Our findings demonstrated no predictive parameter could be assessed and used on this aspect with respect to the factors evaluated for both patient characteristics and NCCT measurements. However, pelvic ap diameter and pelvic lateral diameter measurement values on KUB images were found to be shorter in KUB images and the evaluation of these radiological factors could be helpful in the successful prediction of the likelihood of UAS placement. Further studies to support our findings and look for other radiologic parameters are certainly needed to identify reliable predictive factors on this aspect.

It is clear that prediction of a successful UAS placement could provide certain advantages for the practising urologists in order to outline their policy prior to RIRC procedures. This information will help to the urologist to make decision making well by informing the patient about the possible additional procedures. This will also lower the total cost of the procedures by limiting the use of UAS for a failed attempt.