Safety and Efficacy of Retrograde Intrarenal Surgery for Renal Stones in Patients with a Solitary Kidney: A Single-Center Experience

Abstract

Background and Purpose:

The management of urolithiasis in patients with a solitary kidney is challenging for endourologists. This study was aimed at evaluating the safety and efficacy of retrograde intrarenal surgery (RIRS) in the treatment of such patients with renal stones.

Patients and Methods:

Between January 2010 and January 2014, we enrolled 45 patients who had a solitary kidney and underwent RIRS and holmium:yttrium-aluminum-garnet lithotripsy for the management of renal stones. We collected data pertaining to the preoperative patient characteristics, stone dimensions, and postoperative outcomes.

Results:

Sixty-eight procedures were performed in all. The mean stone diameter was 1.84±0.19 cm (range 0.5–6.0 cm), and the mean operative time, 76.4±40.14 minutes (range 18–190 min). The percentages of patients free of renal stones at the initial and final procedures were 64.44% and 93.33%, respectively. The mean number of procedures needed for the patients with renal stones of diameters ≥20 mm and <20 mm were 1.93 per patient and 1.23 per patient, respectively (P=0.009). Postoperative complications (graded by the Clavien system) were noted in 26.6% of the patients (12/45): Grade I complications, in 20% (9/45); grade II complications, in 4.4% (2/45); and grade III complication, in 2.2% (1/45). The grade III complication was anuria because of Steinstrasse, which necessitated emergency surgery.

Conclusions:

RIRS for the removal of renal stones in patients with a solitary kidney affords a high success rate and low morbidity rate. For patients with large stones, however, a multistaged approach may be needed.

Introduction

The management of nephrolithiasis in patients with a solitary kidney needs careful planning to achieve maximal stone clearance with minimal morbidity. Currently, percutaneous nephrolithotomy (PCNL) and shockwave lithotripsy (SWL) are considered the first-line therapy for intrarenal calculi greater and lesser than 2 cm, respectively. Although PCNL affords high rates of efficacy and stone clearance, it has also been associated with significant morbidity from severe complications, in particular, excessive renal bleeding.¹ SWL, on the other hand, is associated with a lower rate of achieving a stone-free status and a higher rate of repeated procedures than PCNL and flexible ureteroscopy (fURS), especially in cases of large or hard stones.²

Another approach, retrograde intrarenal surgery (RIRS), has generated great interest because of its minimally invasive nature and high success rate; over the past few years, it is being widely used in the treatment of patients with renal stones, even those stones that are large.^3
–5 To our knowledge, however, studies on the efficacy of RIRS for renal stones in patients with a solitary kidney are rare. In this study, we investigated the outcomes of the RIRS procedure and examined its safety and efficacy in the removal of renal stones in patients with a solitary kidney.

Patients and Methods

Study design

We conducted a retrospective analysis of the data of all patients with a single functional kidney and those with congenital or acquired solitary kidney who underwent RIRS at our institution between January 2010 and January 2014. The indications for RIRS in patients with a solitary kidney included failed SWL, contraindication of PCNL, and patient preference. The contraindications of RIRS included severe hydronephrosis and large, staghorn stones. The demographic characteristics of the patient population and their medical and surgical data were collected retrospectively from the medical records of the patients (Table 1). Before the start of the surgery, all patients had undergone preoperative urinalysis, urine culture, intravenous urography, and a helical noncontrast CT scan to determine the anatomy of the collecting system and the location of the intrarenal stones.

Table 1.

Demographic and Clinical Data

Patients, n	45
Sex, male/female	29/16
Laterality, left/right	23/22
Age in years, mean±SD (range)	51.04±1.67 (21–74)
Etiology of the solitary kidney, n
Contralateral nephrectomy	13
Congenital	7
Function	25
Stone size in cm, mean±SD (range)	1.84±0.19 (0.5–6.0)
Site of stone, n
Pelvis	13
Upper calix	1
Middle calix	1
Lower calix	10
Multiple	20

SD=standard deviation.

Surgical technique

Informed consent for the surgery was obtained from all patients. Before the operation, routine preoperative antibiotic therapy was administered. For the surgery, general anesthesia was induced, and the patient was placed in the lithotomy position. An 8F rigid ureteroscope (Karl Storz, Tuttlingen, Germany) was used to assess the ureter visually and advance the guidewire into the kidney. A ureteral access sheath (UAS) (Cook Medical, Bloomington, IN; inner diameter: 9.5F or 12F; outer diameter: 11.5F or 14F) was introduced over the guidewire.

A 7.5F flexible ureteroscope (Storz FLEX-X2, Karl Storz, Tuttlingen, Germany) was then passed through the sheath, in a monorail fashion. The pelvicaliceal system was systematically inspected under manual irrigation and the stones located. A 200-micron holmium laser fiber was then used for lithotripsy at an energy level of 0.4–1.0 J and pulse rate of 10–30 Hz. A 2.4F zero-tipped nitinol stone basket (Cook Medical, Bloomington, IN) was used to remove fragments, if any. At the end of the procedure, the collecting system was again inspected systematically to confirm complete fragmentation. After the lithotripsy, a guidewire was introduced into the renal pelvis, and the sheath and ureteroscope were withdrawn gradually. At the end of the procedure, a Double-J stent was set into position.

A plain radiograph of the kidneys, ureters, and bladder (KUB) was obtained on the first postoperative day and 1 month after the surgery. If a large burden of residual stones was detected, the procedure was repeated until the patient achieved a stone-free status. The stone-free status was defined as the complete absence of residual fragments or as the presence of residual fragments of diameter <2 mm, as seen on the KUB radiograph obtained at four weeks after procedure.

Statistical analysis

Continuous variables were evaluated using the Student t-test, nonparametric and one-way analysis of variance tests, and categorical variables, using the chi-square or Fisher exact test. Statistical significance was set at a P value of 0.05, and all the P values reported were two sided. The data analysis was performed using SPSS Inc. Release 2007, SPSS for Windows, Version 16.0. (SPSS Inc., Chicago, IL).

Results

Between January 2010 and January 2014, 45 patients with a solitary kidney underwent RIRS at our hospital, including 29 male and 16 female patients. During this period, 24 other patients with a solitary kidney had been treated at the hospital, but with PCNL because of a large stone burden, potentially high risk of infection, and/or patient preference. The patients underwent 68 procedures in all, and their mean±standard deviation age was 51.04±1.67 years. The baseline demographic characteristics and etiology of the solitary kidney are detailed in Table 1.

Comorbidities were present in some cases: Hypertension in 15 patients, diabetes mellitus in 4, chronic kidney disease in 7, and cirrhosis with bleeding diathesis in 1 patient. The mean diameter of the stone was 1.84±0.19 cm (range 0.5–6.0 cm). For patients with stones larger than 2 cm, the mean diameter was 3.02±1.53 cm. For patients with stones smaller than 2 cm, the mean diameter was 1.30±0.55 cm. Twenty-two of the 45 (48.89%) patients had previously received treatment: 1 (2.22%) patient each had undergone PCNL and URS (for ureteral stones), 4 (8.89%) had undergone stent placement for acute urinary obstruction, and 16 (35.6%) had undergone stent placement for passive dilation of the ureter.

Nine patients had a positive preoperative urine culture, with four having gram-negative bacterial infection; two, gram-positive bacterial infection; two fungal infection; and one, multiple bacterial infection.

The mean operative time across all the 68 procedures was 76.4±40.14 minutes (range 18–190 min). The number of treatment sessions needed to achieve a stone-free status was one for 30 (66.67%) patients; two for 11 (24.44%) patients; three for 3 patients (6.67%), and four for 1 (2.22%) patient. For the patients with renal stones of diameter <20 mm or ≥20 mm, the mean operative time was 70.97 minutes or 88.43 minutes, and the mean number of procedures needed was 1.23 per patient or 1.93 per patient, respectively.

The stone-free status was achieved in the case of all but 1 patient among those with stones of diameter <20 mm and in 12 (85.71%) of the 14 patients with stones of diameter ≥20 mm (Table 2). The percentages of patients achieving the stone-free status after one and two procedures were 42.86% and 85.71%, respectively. One patient with a large renal stone (6 cm) needed four sessions of RIRS, but did not achieve stone-free status; PCNL was contraindicated in this patient because of the bleeding diathesis. Nevertheless, after the fourth procedure, the maximal diameter of the residual fragments was less than 6 mm.

Table 2.

Perioperative and Postoperative Data

	Total	Stone diameter, ≥20 mm	Stone diameter, <20 mm	P value
n	45	14	31
Operation duration in min, mean±SD (range)	76.40±40.14 (18–190)	88.43±42.96 (35–190)	70.97±38.28 (18–165)	0.170
Procedures, mean (range)	1.44 (1-4)	1.93 (1–4)	1.23 (1–2)	0.009
Postoperative hospitalization time in days, mean±SD (range)	2.16±0.22 (1–7)	2.07±1.33 (1–6)	2.19±1.51 (1–7)	1.00
Drop in Hct level in g/dL, mean±SD (range)	2.79±0.88 (−7.00–35.80)	4.88±9.48 (−1.60–35.80)	1.85±3.10 (−7.00–7.40)	0.477
Initial stone-free rate, % (n/total)	64.44 (29/45)	42.86 (6/14)	74.19 (23/31)	0.042
Final stone-free rate, % (n/total)	93.33 (42/45)	85.71 (12/14)	96.77 (30/31)	0.224
Preoperative serum creatinine in mg/dL, mean±SD (range)	1.29±0.61 (0.49–3.76)	1.20±0.79 (0.49-3.76)	1.33±0.52 (0.57–2.71)	0.106
Postoperative serum creatinine in mg/dL, mean±SD (range)	1.34±0.71 (0.55–4.03)	1.25±0.85 (0.55–4.03)	1.38±0.65 (0.64–3.11)	0.270
Complications, % (n/total)
All	26.6 (12/45)	35.7 (5/14)	22.6 (7/31)	0.47
Grade I	20.0 (9/45)	21.4 (3/14)	19.4 (6/31)	1.00
Grade II	4.4 (2/45)	7.1 (1/14)	3.2 (1/31)	1.00
Grade III	2.2 (1/45)	7.1 (1/14)	0

SD=standard deviation; Hct=hematocrit.

The mean pre- and postoperative serum creatinine levels for the first and second sessions of RIRS were 1.29 mg/dL and 1.34 mg/dL, respectively (P=0.721). Twenty-eight patients showed a slight postoperative decrease in the serum creatinine level, while 10 patients showed a transient elevation of the parameter; the latter was mainly observed among patients with chronic kidney disease (57.1%; 4/7).

Intraoperative complications did not develop in any of the 45 patients, but postoperative complications were recorded in 26.6% of them (12/45). One of the patients had two complications, and the higher grade was used for analysis in this case. The complications were graded according to the Clavien system. Ten patients had transient elevation of the serum creatinine level (Clavien grade I). Two patients had sepsis, but recovered with antibiotic treatment (Clavien grade II). Only one of these two patients had positive preoperative urine culture, but struvite stones were observed during surgery in both patients.

Acute urinary obstruction caused by Steinstrasse developed in two other patients. In one patient, symptomatic Steinstrasse occurred after the removal of the Double-J stent and disappeared spontaneously in 6 hours (Clavien I). In the other patient, the Steinstrasse occurred 10 days after the surgery, causing anuria and acute renal injury despite the presence of the Double-J stent and thereby necessitating an emergency fURS to release the obstruction (Clavien grade III). The serum creatinine levels in this patient returned to baseline levels a few days after the surgery. The mean follow-up period for our patients was 6.18±6.87 months (2–24 mos). None of our patients showed evidence of ureteral stricture during the entire follow-up period.

Discussion

SWL traditionally has been considered the first-line treatment for the removal of small to medium-sized renal stones. fURS, however, is rapidly gaining popularity because of the advancements in endourologic techniques and skills. Further, SWL is limited by relatively low stone-clearance rates, even after repeated sessions, especially when the stones are located in the lower pole of the kidney or are hard in nature.⁶

Resorlu and associates² compared the outcomes of SWL, PCNL, and RIRS for radiolucent renal calculi of diameter 10–20 mm and found that the success rate was lower for SWL than for PCNL, and RIRS (66.5%, 91.4%, and 87%, respectively). Further, the rate of repeated procedure was higher for SWL than for PCNL and RIRS (21.9%, 5.7%, and 8.7%, respectively).

Another drawback associated with SWL is that although relatively noninvasive, shockwaves have the potential to induce vessel rupture and cause hemodynamic instability.⁷ In a recent prospective study of 1300 procedures, the incidence of renal hematoma after SWL was found to be 0.53%, and surgical intervention was necessary only in one patient.⁸ Another large-scale study examining 10,887 procedures of SWL indicated that subcapsular or perirenal hematomas occurred in 20 (0.32%) patients, with 4 of them needing blood transfusion.⁹ Thus, SWL is associated with the risk of the occurrence of a renal hematoma, which, although rare, is a serious complication in patients with a solitary kidney.

On the other hand, PCNL allows for the rapid removal of stones and is associated with high stone-clearance rates. It can lead to significant complications, however, such as severe bleeding (11.2%–17.5%), urinary extravasation (7.2%), colonic injury (0.2%–0.8%), and pleural injury (0.0%–3.1%).¹

For patients with a solitary kidney, PCNL may be associated with high risks of renal replacement therapy because of uncontrollable hemorrhage necessitating embolization or even nephrectomy.^10
–12 This may be attributed to the compensatory hypertrophy occurring in the solitary kidney, which can pose increased risk of hemorrhage on account of increased damage to renal tissue damaged, puncturing of the blood vessels, and dilation of the thick renal parenchyma.¹³

The Clinical Research Office of the Endourological Society Percutaneous Nephrolithotomy Global Study indicated that the transfusion rate in patients with solitary kidneys was up to 10%.¹¹ Canes and colleagues¹⁴ reported a worsening of the glomerular filtration rate in 6.8% of the patients with a solitary kidney managed with PCNL. Thus, PCNL, although beneficial in most cases, may lead to potentially serious complications in patients with a solitary kidney.

RIRS allows the urologists to visualize and manage stones through the naturally existing tracts, and it is associated with a high stone-free rate and low complication rate. The combination of fURS and use of holmium lasers enables effective intracorporeal lithotripsy even in cases in which the stones are hard; SWL alone in such cases is associated with a low stone-free rate.⁴ In addition, theoretically, it may be presumed that RIRS is associated with a lower potential risk of severe renal bleeding than SWL and PCNL, which is particularly important in the case of patients with a solitary kidney. RIRS has been reported to be safe and effective in the management of renal stones in patients with a bleeding diathesis, who are unfit for SWL and PCNL.¹⁵ In our series, severe procedural complications were not observed even after four sessions of RIRS in the patient with large stones and a bleeding diathesis.

With the advances in endoscopic technology, the application of RIRS has extended to include large renal stones. A study on RIRS for renal stones of diameter 2 to 3 cm revealed that the residual fragments were <4 mm and 0–2 mm in 83% and 63% of the patients, respectively.³ Breda and coworkers⁴ have shown that RIRS is efficient in the management of multiple intrarenal calculi, with the overall stone-free rates being 92.2% after an average of 1.4 sessions. Akman and associates¹⁶ compared the outcomes of RIRS and PCNL for renal stones of diameter 2 to 4 cm and found that after the second session, patients undergoing RIRS showed stone-free rates comparable with those of patients undergoing PCNL. Atis and colleagues¹⁷ investigated 24 patients with a solitary kidney who underwent RIRS for renal stones and reported that 8 of the patients with renal stones of diameter >20 mm had initial and final stone-free rates of 72.8% and 90.9%, respectively; in our study group, the corresponding rates were slightly lower (42.86% and 85.71%, respectively), and this finding is likely because of the overall larger stone burdens of our patients.

Concern has been expressed regarding the risk of renal dysfunction associated with the use of high-pressure irrigation during RIRS. Animal studies have shown that high-pressure irrigation (>150 mm Hg) during ureterorenoscopy can lead to parenchymatic damage and focal scarring of the kidney.¹⁸ Rupture of the renal collecting system has also been reported on increasing the renal pressure to 330 mm Hg. Jung coworkers¹⁹ recorded changes in renal pelvic pressure during RIRS and noted that the mean renal pelvic pressure was 33 mm Hg and that the pelvic pressure peaked to as high as 328 mm Hg; however, they did not use the UAS in their procedures.

The use of the UAS in RIRS has been reported to reduce the renal irrigation pressures by about half.²⁰ In our series, the UAS was routinely used in all cases to maintain a low-pressure system. It is difficult to evaluate the effect of RIRS on unilateral renal function in patients with two kidneys. In a study of RIRS on 24 patients with a solitary kidney, no case of postoperative azotemia was observed.¹⁷ Similarly, in our study, no statistically significant difference was noted between the pre- and postoperative mean serum creatinine levels.

In all our patients, we used active extraction of the stone fragments into the nitinol baskets to increase the chances of the patient achieving stone-free status soon after the procedure. Current literature is inadequate with regard to the comparison of the “extracting” and “dusting and go” approaches in the management of intrarenal stones. A randomized study of patients with ureteral stones, however, revealed that the risk of unplanned medical visits was higher in the absence of active extraction of the stone fragments than in the case of intraoperative extraction.²¹ For patients with a solitary kidney, it is important to minimize the risk of events because of impaction of stone to avoid acute renal injury. Therefore, active extraction of the fragments may be useful in precluding the need for ancillary procedures in these patients.

In our series, the UAS was routinely applied in all cases to facilitate stone extraction and maintain low levels of intrarenal pressure. None of our patients had ureteral injury from the insertion of the sheath. This finding is consistent with those of the study by Atis and coworkers¹⁷ who did not observe any case of ureteral wall injuries or ureteral stenosis in patients with a solitary kidney undergoing RIRS. Traxer and associates,²² however, reported that ureteral wall injuries from the insertion of a UAS occurred in 46.5% of their patients, 13.3% of whom had severe injury of the smooth muscle layers. Passive dilation of the ureter by preprocedure stent placement was found to be helpful in decreasing the incidence of severe ureteral injury.²² Thus, the importance of avoiding ureteral damage during the insertion of the sheath should not be undermined in patients with a solitary kidney.

In thus study, anuria caused by Steinstrasse was recorded in the case of two patients, both of whom had renal stones of diameter >2 cm. One of these patients developed anuria while the Double-J stent was still in place. In the study by El-Assmy and colleagues²³ on the outcomes of SWL for patients with a solitary kidney, renal obstruction caused by Steinstrasse was noted in 14 (8.9%) patients. In the study by Soyupek and coworkers,²⁴ the incidence rates of post-SWL Steinstrasse among patients with renal stones of diameters >2 cm, <1 cm, and 1–2 cm were 24.3%, 4.46%, and 15.87%, respectively.

A study by Hyams and colleagues³ on the rate of post-RIRS Steinstrasse indicated an incidence rate of 1.7% among patients with renal stones of 2 to 3 cm in diameter. In their study, Mariani and associates²⁵ reported an incidence rate of 18.7% for post-RIRS symptomatic Steinstrasse in cases of renal stones with a diameter >4 cm. Put together, these findings indicate that the risk of Steinstrasse is high among patients with a solitary kidney, particularly among those with large stones. Therefore, careful attention must be paid to ensure that all the fragments are removed after lithotripsy. A multistage approach may be necessary to avoid acute events because of impaction of the stones.

There are some limitations to this study. First, this is a retrospective study based on analysis of data collected from the medical records of patients. Second, the follow-up duration was short, which made it difficult to evaluate the long-term effects of RIRS on renal function. Third, the analgesic requirement and pain scores of patients who received multistage RIRS were not reviewed to evaluate the discomfort associated with the placement of the Double-J stent. To overcome these drawbacks, it is necessary to undertake prospective studies that are more longitudinal and include a larger sample size, which will enable assessment of the long-term outcome of RIRS on the treatment of patients with a solitary kidney. In addition, long-term follow-up studies are necessary to evaluate the late postoperative complications, such as ureteral stenosis.

Conclusion

Our findings indicated that RIRS is an effective and safe procedure for the removal of stones in patients with a solitary kidney, with a low rate of complications. In cases in which the renal stones are of a diameter >2 cm, however, patients undergoing RIRS may need multiple procedures to achieve a stone-free status.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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