Outcomes of Ureterorenoscopic Stone Treatment in 301 Patients with a Solitary Kidney

Primary objectives

To determine the stone-free rates and intra- and postoperative complication rates and grades of ureterorenoscopic stone treatment in patients with a solitary kidney.

Secondary objective

Study organization and population

This study is a subanalysis of the Clinical Research Office of the Endourological Society (CROES) ureterorenoscopy (URS) Global Study, which is an international observational multicenter study. A total number of 114 Centers in 32 countries participated. The study was initiated in 2010, with each center collecting prospective data on consecutive patients treated with ureteroscopy for urinary stones. Over a 1-year period, 11,885 patients were included. Comprehensive information on the CROESURS study is described elsewhere. ¹¹

Patients included in the current analysis were patients with a solitary kidney who underwent primary or secondary treatment for ureteral or renal stones or a combination hereof. There were 313 patients with a solitary kidney. For 12 of these 313 patients the stone location was not reported. These patients were excluded, leaving 301 patients for analysis.

Follow-up and outcomes

All centers adhered their local treatment and follow-up protocols. Imaging modalities included kidney, ureter, and bladder radiograph, ultrasound or CT scan of the abdomen. A stone-free status was defined as the absence of stones or fragments <1 mm and assessed by the treating physician. Total stone burden was computed as the stone surface area on imaging computed with the formula: length × width × 0.25 × π. ¹² Intraoperative complications included bleeding, mucosal damage, ureteral perforation, ureteral avulsion, conversion, and failure of the procedure. Postoperative complications included bleeding, fever (>38.0°C), urinary tract infection, sepsis, acute abdomen and cerebral, gastrointestinal, pulmonary or cardiac events. Readmission was reported for the 3 months following ureterorenoscopy. Complications were graded using the Clavien–Dindo classification system. ¹³

Data analysis

Patients were divided into three groups based on the anatomical location of the stone: patients with ureteral stones, patients with renal stones, and patients with ureteral plus renal stones.

For the evaluation of the secondary outcomes, the patients with renal stones were divided into two groups: a group who had a preoperative Double-J stent and a group without a preoperative Double-J stent. This approach was also applied to evaluate the difference in outcomes between patients treated with and without the utilization of a UAS. For every group, descriptive data and percentages were based on available data. Chi-square test, Fisher's exact test, Students T-test, and the Mann–Whitney U-test were used to analyze differences in outcomes between patients with and without a preoperative Double-J stent. Multiple logistic regression analyses, with adjustment for confounders, were conducted to evaluate the association between outcomes and the utilization of an UAS. IBM SPSS version 23.0 was used to analyze the data.

Baseline characteristics

There were 219 patients who had ureteric stones, 57 patients with renal stones, and 25 patients with renal stones in combination with ureteric stones. Patient characteristics captured in the database are presented in Table 1. Information on the origin of the solitary kidney was not collected. A large number of the patients had American society of anesthesiologists (ASA) II and III scores. The prevalence of cardiovascular disease (CVD) was high in all groups and varied from 40% to 54%. In the patients with ureteral stones, the stone was located in 51% in the distal-, 19% in the mid-, 23% in the proximal ureter, and 7% in multiple locations of the ureter. The median stone burden for ureter stones was 50 mm². In patients with renal stones, the stone was located in the upper pole in 3.5%, in the interpolar in 5.3%, in the lower pole in 47%, in the renal pelvis in 16%, and in multiple locations in the kidney in 28%. The median burden was 65 mm². In patients with stones in both the ureter and kidney, the median cumulated burden was 140 mm².

Intraoperative procedure

Data with regard to the ureteroscopic procedures are presented in Table 2. Of the total group, 88% received intraoperative antibiotic prophylaxis. A semirigid ureteroscopy was used in 95% of the patients with stones in the ureter. Laser was the most often used fragmentation device to treat renal stones. The median operation time was 40 minutes for ureteral stones, 66 minutes for renal stones, and 74 minutes for renal stones in combination with ureteral stones. In the renal stone group, 47% of the patients were presented, and an UAS was used in 67% of the cases. A postoperative ureteral stent was placed in 87% of the patients.

Stone-free rates and retreatment rates

Postoperative outcomes are presented in Table 3. The overall stone-free rate after ureteroscopy for ureteral stones was 89%. In this group, 23 (10.5%) needed retreatment within a period of 3 months. In the renal stone group, the overall stone-free rate was 56.4%. The stone-free rate for stones ≤80 mm² was 82%. Retreatment was needed after 17.5% of the procedures. The overall stone-free rate in the group of patients with ureteral stones in combination with renal stones was 60.0%. The stone-free rate for stones ≤80 mm² was 71% and 56% for stones >80 mm². In this group, 6 (24%) patients needed retreatment. An overview of stone-free rates stratified by different imaging modalities used for the evaluation of stone-free status is presented in Table 4.

Complications

Results on intra- and postoperative complications are presented in Table 2. In the ureteric stone group, the overall intraoperative complication rate was 7.4%. One avulsion of the ureter was reported while treating an impacted stone. Postoperative complications occurred in nine (4.1%) of the patients. The most severe complication was sepsis, reported in one patient.

In the renal stone group, the intraoperative complication rate was 7.0%. The postoperative complication rate was 10.5%, comprising of four Clavien I–II and two Clavien IVa complications.

In the group of patients with ureteral stones in combination with renal stones intraoperative complications were reported in three (12%) and postoperative complication in three (12%) of the patients. In this group, no severe complications were reported.

In the total cohort, one patient needed blood transfusion. The reason for transfusion was not recorded. No intra- or postoperative complications were reported in this patient.

Within the follow-up period of 3 months one ureteral stricture was reported after treatment for an impacted ureter stone.

Preoperative ureteral stent

Patient characteristics and outcomes of ureterorenoscopy for renal stones in patients with and without a preoperative Double-J stent are presented in Table 5. Patient baseline characteristics matched well between the groups except from the prevalence of CVD, which was 63% in the presented group and 40% in the group without a preoperative Double-J (p = 0.083). In the presented group, more patients underwent a prior ureterorenoscopic stone treatments compared with the patients without a preoperative Double-J stent (42% vs 20%, p = 0.087). Patients without a preoperative Double-J stent had relatively more PCNL and SWL procedures reported in their stone treatment history, but without a significant difference if compared with the Double-J group. There was no statistically significant difference between the stone burdens. The median operation time was 70 minutes in the group with a preoperative Double-J stent and 55 minutes in the group without a stent (p = 0.17). There were no significant differences in stone-free rates, retreatment rates, and intra- and postoperative complications rates.

Ureteral access sheath

Patient characteristics and treatment outcomes for patients with and without utilization of a UAS are presented in Table 6. The prevalence of diabetes mellitus and CVD was higher in the UAS group, but without a statistically significant difference. Pre- and postoperative placement of a ureteral stent was more frequently performed in the UAS group. The median stone burden was 71 mm² in the UAS group and 108 mm² in the non-UAS group (p = 0.51). Despite the lower stone burden, the SFR was lower in the UAS group than in the non-UAS group (51% vs 65%, p = 0.22). By way of contrast, we found a higher retreatment rate of 27% in the non-UAS group compared with 13% in the UAS groups (p = 0.16). Intraoperative complications occurred in 11.1% of the UAS group and in 5.4% of the non-UAS group (p = 0.45). Postoperative complications occurred in 8.9% in the UAS group and in 13.5% of the non-UAS group (p = 0.73). Multiple logistic regression analyses with adjustment for confounders revealed no associations, neither between utilization of a UAS and higher SFRs nor between UAS use and lower intra- and postoperative complication rates. The full uni- and multivariate models can be found in Supplementary Table S1 (Supplementary Data are available online at www.liebertpub.com/end).

Ureteral stone treatment

Stone-free rates after ureteroscopy for ureteral stones varied from 89% for smaller stones to 87% for larger stones. Sizeable studies have been published reporting the results of ureteroscopy for ureteral stone treatment in patients with bilateral kidneys. A study by Castro and colleagues determined stone-free rates and complication rates in a large cohort of 9681 patients. For small stones (≤10 mm), they report stone-free rates ranging from 95% in the distal ureter to 86% in the proximal ureter. For larger stones (>10 mm), stone-free rates ranged from 91% in the distal ureter to 83% in the proximal ureter. ¹⁴ Likewise, European Association of Urology (EAU) and American Urological Association (AUA) guidelines report similar stone-free rates in populations of patients with bilateral kidneys. ^4,3 Stone-free rates found in this study correspond well with stone-free rates reported in large groups of patients with bilateral kidneys.

Intra- and postoperative complications rate were 7.4% and 4.1%, respectively. Castro and colleagues found similar complication rates of 3.8% to 7.7% for intraoperative complications and 2.5% to 4.6% for postoperative complications, varying according to ureteral stone location. ¹⁴

Renal stone treatment

A few studies have evaluated outcomes of ureteroscopic stone removal in patients with a solitary kidney. Atis and colleagues reported outcomes in 24 patients. Stone-free rates were 83.3% and 95.8% after the first and second procedure, respectively. Postoperative Clavien grade I and II complications occurred in 16.6% of the patients. ⁵ A study by Gao and colleagues evaluated the outcomes of ureteroscopy in 45 patients with a total of 68 procedures. The stone-free rate at the initial procedure was 64% and 93% after the final procedure. For stones <20 mm, the mean number of procedures was 1.23 per patient and 1.93 for stones ≥20 mm. Postoperative complications were reported in 26.6% of the patients, and 20% of them were Clavien grade 1 complications. ⁷ Yuruk and colleagues published a retrospective study to compare the outcomes of 18 patients who underwent ureteroscopy and 30 patients who underwent SWL in a solitary kidney. Stone-free rates at the third postoperative month were 73.3% for SWL and 66.6% for URS (p = 0.623). Patients in the SWL group needed an average of 2.2 sessions, and in the URS group, 1.06 sessions to achieve a stone-free status. ⁶ Ghosh and colleagues reported the outcomes of 18 patients. The initial stone-free rate was 82%, and one Clavien grade II complication was reported. Finally, Giusti and colleagues published a prospective study in 29 patients with a solitary kidney. The median follow-up time was 36 months. They report a primary stone-free rate of 72% and a secondary rate of 93%, with a mean number of 1.24 procedures per patient. Clavien grade I complications occurred in 27% of the patients, and no major complications were reported. ⁸ All of the above mentioned studies compared pre- and postoperative kidney function, and none of the studies reported statistically or clinically significant deterioration of kidney function. In conclusion, these studies found that ureteroscopy is effective and a safe treatment modality for stones in a solitary kidney. Stone-free rates as well as complication rates and grades are in line with the results of this current study. Nevertheless, these prior studies also report the requirement of auxiliary procedures, but most of them do not specify a cutoff point for stone burden. We found that stone-free rates for single session treatment decreased when treating larger (>80 mm², ∼10 mm) kidney stones. If only a single-session treatment is preferred, then (mini-) PCNL is a valuable alternative. Although the complication risk for PCNL is higher, especially in a solitary kidney, effectiveness and complication risks have to be balanced accurately.

Bucuras and colleagues compared outcomes of PCNL in 189 patients with a solitary kidney with outcomes of PCNL in patients with bilateral kidneys. They found that patients with a solitary kidney had high ASA-scores and a high prevalence of CVD compared with patients with bilateral kidneys. This high prevalence of comorbidities corresponds with the findings of this study. Bucuras and colleagues also found that patients with a solitary kidney had higher levels of renal impairment, lower stone-free rates (65% vs 76%), and higher transfusion rates. Bleeding complications occurred in 10% of the patients, and all of these patients needed blood transfusion. ¹⁵

Last decade's minimal invasive refinements such as micro- and (ultra)mini-PCNL were designed to reduce access-related complications. These techniques could especially be interesting to reduce bleeding complications and to preserve nephrons in a solitary kidney. Hitherto, the outcomes of the studies performed are promising; these techniques are still in their infancy and require further study. ¹⁶

Either way, ureterorenoscopy and PCNL are both valuable options for the treatment of larger renal stones. PCNL seems to be more effective but with higher bleeding risks, whereas in case of ureteroscopy, a staged procedure is more often required to attain a stone-free status.

Reduction of the bleeding risk is paramount to perform a safe procedure. The renal compensatory hypertrophy in a solitary kidney was found to be a risk factor for bleeding. ¹⁷ In addition, the high prevalence of CVD found in this study, with the need for anticoagulants, is a risk factor. Hence, this could also be a point of action to reduce bleeding complications. Under such circumstances, it is always recommended to consult the treating physician and ask for the possibility to bridge or intercalate a stop during the perioperative period and be as conservative as safety allows.

Assimos and colleagues found the solitary kidney to be a predictor for the placement of a preoperative ureteral stent. ¹⁶ We performed a subanalysis to evaluate possible differences in outcomes for ureterorenoscopy between patients with a preoperative Double-J stent and patients without a preoperative stent. There were no significant differences between outcomes. Regardless, we found a nonsignificant but notable longer operation time in the group that was presented. Assimos and colleagues also reported longer operation time in presented patients compared with patients without a preoperative stent in patients with bilateral kidneys. ¹⁶ This may be due to the time needed for stent removal at the beginning of the procedure. Overall, short-term outcomes were acceptable in the group without a preoperative stent and comparable with those of patients who were presented. As to the usefulness of presenting, it can alleviate the urinary obstruction and sometimes the infection of the upper tract. The design of this study is not optimal to draw a firm conclusion about the need to prestent and unfortunately the reason for Double-J placement was not reported.

In this study, a postoperative stent was placed in 87% of the procedures. The AUA-guideline states that a solitary kidney is a clear indication for consideration of placing a postoperative stent. Based on expert opinion, the AUA also recommends to use a safety guide wire for most endoscopic cases. ² In this study, six ureteral perforations and one ureteral avulsion were reported in a total of 301 cases. For this reason, a safety guide wire is advisable to facilitate rapid reaccess or placement of a ureteral stent when the ureter is at risk.

Limitations

This study design contains two main limitations. First, the type of imaging modality used for preoperative stone size calculations was not recorded in this registry study. Although a preoperative CT scan is common practice in participating centers, some measurements may be based on alternative imaging modalities, resulting in a less accurate determination of stone burden. Second, the imaging protocol for the postoperative evaluation of stone-free status is nonuniform, leading to ambiguity in the definition of stone-free status. The ideal study design requires a pre- and postoperative low dose CT scan, but this is not common practice yet. Nonetheless, this may be a feasible approach in near future as radiation exposure of CT scans has been decreasing progressively.

Next, the design of this study does not provide us to evaluate outcomes after staged procedures with a long-term follow-up. Hence, the prior-performed and above-mentioned studies are providential in this information.

Dependent on multiple factors, including the estimation of bleeding risks, a choice should be made to use the preferred modality acuminated on each single case. In future, research (minimal invasive) percutaneous options should be further explored and compared with ureteroscopy, also in patients with a solitary kidney. Next, a long-term follow-up could help to evaluate the risk of complications such as deterioration of kidney function and the appearance of severe complications such as ureteral strictures and terminal renal insufficiency.