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.