WCE 2018: Assessment of Residual Stone Fragments after Retrograde Intrarenal Surgery

Paris, France (UroToday.com) Following retrograde intrarenal surgery (RIRS), residual stone fragments can be common and can cause symptoms or even additional procedures. There is no current consensus in the literature regarding imaging techniques after RIRS to assess residual fragment stone burden. One imaging method widely accepted in literature is the gold standard non-contrast computed tomography (NCCT) for evaluation of urolithiasis. During his moderated poster session, Dr. Danilovic sought out to define a suitable approach to assess residual stone fragments after RIRS.

Dr. Danilovic prospectively studied 92 patients who had RIRS for symptomatic stones that were diagnosed by NCCT. The stones were either >5 mm and <20 mm or <15 mm in the lower calyx. Any residual stone fragments were assessed with endoscopic evaluation at the end of the RIRS procedure. These patients also received NCCT, ultrasound, and KUB x-rays 90 days after their procedure. Radiologists who looked at the images were blinded for the different evaluation methods.

The team found their stone free rate by NCCT to be 74.8% with 0 - 2 mm in 8.7% and >2 mm residual fragments in 16.5% renal units. Interestingly, there were no cases of residual fragments > 2 mm on NCCT if their endoscopic evaluation after the procedure did not show fragments. Residual fragments were noted in 62.6% renal units at endoscopic evaluation and in 25.2% on post-operative day (POD) 90 NCCT, resulting in a clearance rate of 59.7%. 

One of the most striking findings was that stone free status by endoscopic evaluation at the end of RIRS was comparable to NCCT in 93% of the cases. Ultrasound (US) misdiagnosed stone free renal units as residual fragments >2 mm in up to 25.6%. After evaluation with US and KUB, neither were able to identify residual fragments between 0-2 mm. 

In conclusion, NCCT was considered to be the gold standard for the evaluation of residual stone fragments after RIRS according to Dr. Danilovic. The group also proposed an algorithm (see figure below) for imaging after RIRS procedure. For the follow-up imaging after RIRS, they suggest that if endoscopic evaluation resulted stone-free or residual fragments were between 0 – 2 mm, a POD 90 NCCT could be performed. The ultrasound could potentially be used if the endoscopic evaluation after surgery showed residual fragments > 2 mm. This algorithm was surely set up for some debate. One member from the audience questioned whether it was necessary to even do NCCT for stones less than 2 mm if the patient would likely pass it without issue. It is important to keep in mind the ionizing radiation from NCCT as it is certainly a growing issue today and should be avoided as much as possible. Dr. Danilovic answered back that with a NCCT one could achieve not only a confident stone free rate but also more importantly look for potential complications such as subcapsular hematomas.


Presented by: Dr. Alexandre Danilovic, Department of Urology, Hospital das Clinicas, University of Sao; Paulo Medical School, Sao Paulo, Brazil

Authors: Alexandre Danilovic, Andrea Cavalanti, Bruno Rocha, Olivier Traxer, Fabio Torricelli, Giovanni Marchini, Eduardo Mazzucchi, Miguel Srougi, Department of Urology, Hospital das Clinicas, University of Sao; Paulo Medical School, Sao Paulo, Brazil

Written by: John Sung, Department of Urology, University of California-Irvine, medical writer for UroToday.com. at the 36th World Congress of Endourology (WCE) and SWL - September 20-23, 2018 Paris, France