Discussion
Surgical management of kidney stones relies mainly on the size and location of the stones. Percutaneous nephrolithotomy (PCNL) is the standard procedure for kidney stones larger than 2 cm, and SWL or RIRS is recommended for those smaller than 2 cm 1,2. However, RIRS obtains a much more common use than is approved in current urology practice 15,16 because ’flexible URS is less invasive than PCNL but often with higher stone-free rates than SWL’17.
In the current study, we applied a second-look flexible URS following the RIRS procedure, regardless of stone size, thus increasing the SFRs and reducing the probability of stone related events. Definition of SFR is no stone fragments at any size except for stone size less than 1 mm. We argue that using a second-look flexible URS in the same session with stent removal has some advantages, such as no need for additional anesthesia due to SREs, higher SFRs, and no radiation exposure for SFR confirmation.
The most desirable conditions following a successful RIRS procedure are a complete flush-out of all stone fragments and no SREs18. Great treatment results have been reported following RIRS. In the CROES study, high SFR (85.6%) and low complication rate (3.5%) were preserved 9. Guisti et al. observed that SFR values were highest (90.5%) in small stones at 1 cm but declined when the stone size increased. (1-2 cm, 2–3 cm and> 3 cm in diameter with 78.8%, 70.5% and 55% respectively) 10.
There are also studies reporting different SFRs when focusing on subgroups. In a review of seven RIRC studies, it was observed that SFRs ranged from 34.8% to 59.7%, with Non-Contrast CT performed in the first three months postoperatively. 3.7% to 35% of these patients had to undergo stone surgery again 11. Similarly, Rippel et al. reported a 38% SFR in patients who underwent CT control in the postoperative period following RIRS 12.
Clinically insignificant kidney stones may not be ’insignificant’, and RSFs remain a ’thorny’ issue for both patients and urologists.13. Stone free status following RIRS is an independent predictor for hospital re-admission and re-hospitalization3. One study reported that RSF greater than 4 mm would have a 59% probability of SRE, and 38% would need reoperation. However, even if the RSF is smaller than 4 mm, the stone’s size will increase by 28% of this patient group, and 18% will need reoperation19. Complications associated with flexible URS risen from 7.7% in the perioperative period to 25.4% in the first 30 days after discharge 20.
Hein et al. have studied factors influential on SREs in patients who have been followed for five years after RIRS. They showed that RSF of 1 mm or smaller after RIRS has a potential risk for SREs21. They concluded that RIRS should aim for complete stone clearance and that all RSFs should be considered significant regardless of size. In the current study, we improved our SFR and achieved lower SREs with a second-look flexible URS. Our SRE rate for the whole cohort was 31.25% (n=55/176) at a mean follow-up of 21 months; it was higher in group 1 (56.9%) than group 2 (20.8%), a finding that supports the conclusions of Hein and colleagues.
The natural history of asymptomatic kidney stones is another controversial issue in the literature. Small, non-occlusive calyceal stones have the potential to both grow and cause pain.22. SRE is observed in more than half of asymptomatic stone patients, 5-year average SRE observation rate is 51.2%, and 14.3% had to go to the emergency department. 23.
Our radiologically confirmed RSFs (>= 1 mm) after RIRS in group 2 was 59.2%. Remarkably, this decreased to 6.4% after the second-look flexible URS procedure (p<0.001) (Table 2). Stone-related event-free patients increased significantly, from 43.14% in group 1 to 79.2% in group 2 (Table 1). Although we failed to show a significant association with RSFs in the SRE multivariable analysis, we found a significant difference between group 2 and group 1 (OR: 8.48) (Table 2). For this reason, we conclude that second-look flexible URS is beneficial because it decreases RSFs and SREs.
In our clinical practice, stent removal is performed at two weeks postoperatively. Simultaneous intervention for single or multiple stones that are retractable with a basket during stent removal provides economic and work-related advantages that may improve patient satisfaction.
Like previous studies, the current study defines SREs to include stone growth, urinary infection, an emergency room visit, or additional intervention 6,24. This study found that, at a mean follow-up of 21 months, 31.25% (n=55/176) of the whole cohort were observed to have SREs, although 6.8% (n=12/176) of those stones were asymptomatic.
Radiologically evaluated postoperative SFR after RIRS was 37.25% and 40.8% in group 1 and group 2, respectively. This difference was not statistically significant. Although we report an immediate intraoperative SFR of 57.6% (n=72/125) for group 2, this proved to be 40.8% (n=51/125). The difference may be due to unfavorable intraoperative conditions such as bleeding or dusting caused by low visibility. Finally, SFR increased to 93.6% after second-look flexible URS. These RSFs easy to identify when there is no dust or bleeding exists. Regarding SFR, CT scan more accurate than immediate intraoperative SFR; it carries an additional radiation exposure.
Non-Contrast CT is recommended for detecting residual stones following RIRS 2 but stone patients are often at risk of exposure to excessive radiation. International Commission on Radiological Protection (ICRP) reported thresholds for safe exposure as 50 mSv for a single year or 20 mSv per year for five years25. Five-year retrospective radiation exposure of patients referred to a tertiary clinic for stone treatment was analyzed. Even based on CT examinations alone, it was found that 26% of these patients were exposed to more than 20 mSV per year and 6% more than 50 mSV per year 26. It has been reported that the patients who applied to the emergency department due to acute SRE were exposed to an average of 29.7 mSv (IQR 24.2, 45.1) radiation, and 20 percent of them were exposed to more than 50 mSv in the 1-year follow-up27. We examined all patients radiologically with X-ray KUB and ultrasonography during follow-up; CT imaging was not performed of any patient.
Various techniques and methods have been reported in the literature to achieve a completely stone-free status and to reduce radiation exposure, including artificial intelligence algorithms. 14. A study aimed to detect residual stone fragments with the ”Endoluminal control” method. All calyceal spaces are re-controlled after lithotripsy during flexible URS; a 97% success rate has been reported compared to CT results after 4 to 8 weeks. In only one patient, they reported that a 2 mm residual stone fragment was missed. The authors claimed that a CT was not required to reduce radiation exposure when residual stone fragments were not seen after endoscopic control 28.
Danilovic et al. showed that SFR following RIRS was 93.0% accurate compared to CT when endoscopically controlled. There were no cases of RSF> 2 mm in CT for patients who were evaluated as stone-free on endoscopic evaluation 29.
The term ”second-look flexible URS” was first used by Breda et al. They used second-look flexible URS as a final diagnostic inspection after a single or repeated RIRS to confirm stone-free status. In that study, 37% (n=19/51) of the patients had two or more RIRS procedures. Their overall SFRs after the first and second RIRS were 64.7% and 92.2%, respectively. While their SFRs for stones ≤2 cm at first and second RIRS were 79% and 100%, respectively, the SFRs for stones >2 cm were 52% and 85.1%, respectively 30. Although they argued that the need for a second-look flexible URS would decrease with experience, our results refute this viewpoint because our group 2 had a significant decrease in SRE rates (OR: 8.48-95%; CI: 2.95-24.42). For this reason, we believe that a routine second-look flexible URS at the time of stent removal may help reduce SREs.
Non-randomized, the retrospective design is the most important limitation of this study. Although we excluded data from the first 50 patients in the study to eliminate patients treated during the learning curve, we found that patients in group 1 were operated on relatively earlier than patients in group 2, which may be a source of bias in favor of patients in the group 2 in terms of surgical expertise. Unfortunately, we were unable to conduct a cost analysis, so further studies may help quantify the economic implications of using second-look flexible URS.