Flexible Ureteroscopy and Laser Lithotripsy for Stones >2 cm: A Systematic Review and Meta-Analysis

Abstract

Background and Purpose:

Urinary stones >2 cm are traditionally managed with percutaneous nephrolithotomy (PCNL). Recently, flexible ureteroscopy and laser lithotripsy) (FURSL) has been used to manage them with comparable results. In a comparative study of renal stones between 2 and 3 cm, FURSL was reported to need less second-stage procedures and be just as effective as PCNL. Our purpose was to review the literature for renal stones >2 cm managed by ureteroscopy and holmium lasertripsy.

Materials and Methods:

A systematic review and quantitative meta-analysis was performed using studies identified by a literature search from 1990s (the first reported large renal stones treated ureteroscopically) to August 2011. All English language articles reporting on a minimum of 10 patients treated with FURSL for renal stones >2 cm were included. Two reviewers independently extracted the data from each study. The data of studies with comparable results were included into a meta-analysis.

Results:

In nine studies, 445 patients (460 renal units) were reportedly treated with FURSL. The mean operative time was 82.5 minutes (28–215 min). The mean stone-free rate was 93.7% (77%–96.7%), with an average of 1.6 procedures per patient. The mean stone size was 2.5 cm. An overall complication rate was 10.1%. Major complications developed in 21 (5.3%) patients and minor complications developed in 19 (4.8%) patients. A subgroup analysis shows that FURSL has a 95.7% stone-free rate with stones 2–3 cm and 84.6% in those >3 cm (P=0.01), with a minor complication rate of 14.3% and 15.4%, respectively, and a major complication rate of 0% and 11.5%, respectively.

Conclusion:

In experienced hands, FURSL can successfully treat patients with stones >2 cm with a high stone-free rate and a low complication rate. Although the studies are from high-volume experienced centers and may not be sufficient to alter everyday routine practice, this review has shown that the efficacy of FURSL allows an alternative to PCNL.

Introduction

H istorically, renal stones larger than 2 cm were managed with percutaneous nephrolithotomy (PCNL), shockwave lithotripsy (SWL), or a combination of both and, in rare instances, an open procedure.^1
–3 PCNL is considered the gold standard treatment for large stones with a clearance rate of 77% to 95%.^1

–5 SWL has an overall stone-free rate (SFR) of 23% to 57%, and the rate decreases with increasing stone size.^2,4 Combined therapy, PCNL+SWL, only slightly increases the SFR to 66%, but necessitates, on average, 3.3 procedures per patient; therefore, it is not an ideal management strategy.² Open surgery has been relatively abandoned for the management of stones, with only a selective indication, such as patients with complex collecting systems, excessive morbid obesity, or extremely poor function of the affected renal unit.²

The last decade has witnessed not only technical advancements in endoscopic procedures and equipment, but also an increase in surgical skills using them.^3,6,7 The development of smaller diameter scopes, increased scope flexibility, improvement of accessories, and holmium laser technology has led more urologists to attempt management of large renal stones with flexible ureteroscopy and laser lithotripsy (FURSL). The resulting SFRs were comparable to those of PCNL.^3,4,8 Indeed, studies report a SFR of 88% to 92% in patients with large stones.^3,4

To this end, we aimed to conduct a systematic review and a meta-analysis to assess the efficacy and safety of FURSL in the treatment of patients with renal stones larger than 2 cm. Our secondary aim was to assess the operative times, number of procedures per patient needed to achieve a SFR, average stone size, and the use of ureteral access sheaths.

Materials and Methods

Search strategy and study selection

The systematic review was performed according to the Cochrane reviews guidelines. The search strategy was conducted to find relevant studies from MEDLINE (1990–August 2011), EMBASE (1990–August 2011), Cochrane Central Register of Controlled Trials-CENTRAL (in The Cochrane Library-Issue 1, 2011), CINAHL (1990–August 2011), Clinicaltrials.gov, Google Scholar, and individual urologic journals.

Terms used included: “ureteroscopy,” “flexible ureteroscopy,” “large stones,” “stones >2 cm,” “urolithiasis,” “renal,” “calculi,” “laser,” and “lasertripsy.”

Mesh phrases included: (“Ureteroscopy"[Mesh]) AND “Urinary Calculi"[Mesh] and (“Ureteroscopy”[Mesh]) AND “Urinary Calculi”[Mesh]) AND “Lasers, Solid-State”[Mesh].

Articles in languages other than English were included if data were extractable and references of searched papers were evaluated for potential inclusion. Authors of the included studies were contacted wherever the data were not available or not clear.

Two reviewers (OA and BS) identified all studies that appeared to fit the inclusion criteria for full review. Each reviewer independently selected studies for inclusion in the review. Disagreement between the two extracting authors was resolved by consensus by all authors.

Data extraction and analysis

Studies relevant to ureteroscopic management of patients with stones larger than 2 cm were included. The following variables were extracted from each study: Period of the study, country of origin of the study, number of patients included, operative time, SFRs after completion of management, number of procedures per patient, stone sizes, and complications. The data of each study were grouped into a meta-analysis, in an intention to treat basis, to allow a numerical representation of the results. Data that were similar were pooled and included for the meta-analysis. Furthermore, a subgroup analysis was conducted to evaluate the SFR, mean number of procedures, and complications in patients with stones 2 to 3 cm and in those with stones >3. For continuous data a Mantel-Haenszel chi-square test was used and for dichotomous data an inverse variance was used.

A quality assessment of harms using the McHarm scale, was conducted for each included study.⁹ This was deemed appropriate by all reviewers because we were analyzing safety as well as efficacy of ureteroscopic treatment of large stones. We used Review Manager (RevMan 5.0.23) to plot the quality assessment of harms tables.

Results

The literature search yielded 296 studies, of which 273 were excluded because of nonrelevance based on titles (252) and abstracts (21) (Fig. 1). These titles and abstracts of the studies did not focus on FURSL or large stones; hence, the exclusion. Full manuscripts were evaluated in 23 studies, of which, 9 were included into the review.^{4

–8,10

–13} The majority of the studies were published within the last 3 years, reflecting the increased use of FURSL for fragmentation of large stones.^{4
–6,10,11,13}

FIG. 1.

Flowchart for article selection of the review.

All included studies were cohort observational studies, with no randomization or control groups and reported on FURSL for renal stones larger than 2 cm. All studies reported on the variables indicated in the data extraction section and are plotted in Tables 1 and 2. Tables 3 and 4 delineate patients grouped into stone size 2 to 3 cm and >3 cm.

Table 1.

Study and Patient Demographics

Author	Journal	Center, Country	Year	Number of patients (renal units)	Mean age (average)	Male:female
Grasso⁸	J Urol	New York University, USA	1998	51 (63)	No mentioned (10–77)	33:18
El-Anany¹²	BJU Int	Assiut University Hospital, Egypt	2001	30	43 (18–62)	22:8
Breda⁷	J Urol	David Geffen School of Medicine, UCLA, USA	2008	15	56.4 (39–70)	10:5
Riley⁶	J Endourol	University of Missouri, USA	2009	22	52.1 (25–78)	16:6
Breda 2009¹¹	Eur Urol	David Geffen School of Medicine, UCLA, USA	2009	27	Not clear	Not clear
Bader¹⁰	Urol Res	University Hospital Großhadern, Germany	2010	24	55.8 (20–78)	11:13
Hyams¹³	J Endourol	New York University School of Medicine, USA	2010	120	55.7±12.8	72:48
Al-Qahtani⁴	Adv in Urol	Tenon University Hospital, Pierre and Marie Curie University, France	2011	120 (123)	48±15.3	59:64
Hussain⁵	J Endourol	Maidstone Hospital, UK	2011	36	Not clear	Not clear
Total				445 (460)	10–78	223:162

USA=United States of America; UCLA=University of California, Los Angeles; UK=United Kingdom.

Table 2.

Review of All Literature for Renal Stones >2 cm Managed with Flexible Ureteroscopy and Laser Lithotripsy

Author	Mean operative time (min)	SFR after treatment completion	Mean number of procedures	Mean stone size (cm)	Use of access sheath	Minor complications	Major complications	Total complications
Grasso⁸	Not mentioned	93%	1.3	2.4	Not mentioned	0	3 (CVA: 1; hematuria and clot retention needing transfusion: 1; pyelonephritis: 1)	3
El-Anany¹²	85 (55–160)	77%	Not mentioned	>2 cm	Not mentioned	2 (fever: 1; hematuria: 1)	0	2
Breda⁷	83.3 (45–140)	93%	1.4	2.2	15/15	3 (fever/pain: 1; hematuria: 2)	0	3
Riley⁶	72 (28–138)	91%	1.82	3	22/22	3 postoperative pain	2 (ITU admission with bacteremia: 1; subcapsular hematoma: 1)	5
Breda 2009¹¹	66	85%	1.6	>2 cm	27/27	Not clear	Not clear	Not clear
Bader¹⁰	114.1 (50–215)	92%	1.7	3	24/24	3 UTI	1 (Steinstrasse: 1)	4
Hyams¹³	Operating room time: 102.7±20.6Surgical time: 74.3±20	97.5%^a	Not mentioned	2.4	80/120	3 (acute retention: 1; fever: 1; UTI: 1)	5 (perforation: 1; obstructive pyelonephritis: 1; Steinstrasse: 2; subcapsular hematoma: 1)	8
Al-Qahtani⁴	89.1 (60–140)	96.7%	1.6	2.6	117/123	5 (hematuria: 3; UTI: 1; intraoperative bleeding: 1)	10 (perforation: 1; fornix rupture: 3; prostatitis: 1; obstructive pyelonephritis: 1; Steinstrasse: 2; subcapsular hematoma: 2)	15
Hussain⁵	Not mentioned	94.4%	Not clear	2.8	Not mentioned	Not mentioned	Not mentioned	Not mentioned
Total (mean)	82.5^b	93.7%	1.6	2.5	86% (285/331)	4.8% (19/397)	5.3% (21/397)	10.1% (40/397)

SFR=stone-free rate; CVA=cerebrovascular accident; UTI=urinary tract infection.

Study mentions that after 18-month follow-up, 3/120 patients needed reoperation for residual stones.

The surgical time was what was counted into the meta-analysis.

Table 3.

Subgroup Analysis Stratified to Stones 2 to 3 cm

Author	Number of patients	SFR after treatment completion	Mean number of procedures	Minor complications	Major complications
El-Anany¹²	23	86.95%	Not mentioned	Not mentioned	0
Breda⁷	15	93%	1.4	3 (fever/pain: 1; hematuria: 2)	0
Riley⁶	10	90%	1.6	1 postoperative pain	0
Bader¹⁰	10	90%	1.4	1 UTI	0
Al-Qahtani⁴	104	98%	Not mentioned	Not mentioned	Not mentioned
Total (mean)	162	95.7%	1.46	5 (14.3%)	0%

SFR=stone-free rates; UTI=urinary tract infection.

Table 4.

Subgroup Analysis Stratified to Stones >3 cm

Author	Number of patients	SFR after treatment completion	Mean number of procedures	Minor complications	Major complications
El-Anany¹²	7	42.9 %	Not mentioned	Not mentioned	0
Riley⁶	12	91.7%	1.83	2 postoperative pain	2 (ITU admission with bacteremia: 1; subcapsular hematoma: 1)
Bader¹⁰	14	92.9%	1.86	2 UTI	1 Steinstrasse
Al-Qahtani⁴	19	89.5%	Not mentioned	Not mentioned	Not mentioned
Total (mean)	52	84.6%	1.85	4 (15.4%)	3 (11.5%)

SFR=stone-free rates; ITU=intensive treatment unit; UTI=urinary tract infection.

After reading the full manuscripts, we excluded 14 studies. Eight of these studies were not related to FURSL of large stones. Three looked at combined electrohydraulic and holmium laser treatment of stones where the electrohydraulic treatment was the main procedure.^1,14,15 Two other studies had patients with stones larger than 1 cm.^3,16,17 The last study overlapped with a similar included study from the same authors.^13,18 While the included study was more focused on the FURSL treatment of large stones, the excluded study was aimed at comparing PCNL with FURSL.¹⁸

Characteristics of the included studies

The studies were published between 1998 and 2011, with majority conducted in the United States (5/9), three conducted in Europe, and one in Africa. There were 460 renal units in 445 patients with an age range between 10 and 78 years. There were 1.4 times as many men as there were women (Table 1). All the studies reported on FURSL of stones >2 cm.

With regard to the main outcome of efficacy, all nine studies reported on SFRs, and eight studies reported on complications; however, Breda and associates (2009) was not clear on whether complications occurred in patients with stones larger or smaller than 2 cm and therefore this information was left out of the meta-analysis.^{4,6
–8,10

–13} Two studies were from the same institute, but were on different cohorts of patients; therefore both studies were included.^7,11 Hussain and colleagues⁵ only reported on SFRs of varying sized stones with no mention of any other outcome that could be included. Six studies reported on the average number of procedures performed,^{4,6
–8,10,11} with seven studies reporting on the average operative time.^{4,6,7,10

–13} A further five studies reported their use of ureteral access sheath.^{4,6,7,10,11,13} All studies reported on stone size. One article had included one child with a large renal stone, while the remaining cohort were adults; therefore, the study was included because the authors did not think one patient's results can skew the final outcome.⁸ Furthermore, two of studies just mentioned that the stones were larger than 2 cm rather than the average and therefore this information was excluded from the meta-analysis.

In five studies, the data for the subgroup analysis were performed; however, only SFR data were available for all five of the studies.^4,6,7,10,12 Mean procedure number and minor complications were analyzed in three studies in the 2 to 3 cm group and two in the 3 cm group (Tables 3 and 4), while major complications were analyzed in four studies in the 2 to 3 cm group and two in the 3 cm group (Tables 3 and 4).

Meta-analysis results

The combined data of the included studies showed that FURSL had an average SFR of around 93.7% (77%–97.5%) with an average of 1.6 procedures per patient.

Concerning complications, the combined data had an overall complication rate of 10.1%, with minor complications developing in 19 (4.8%) patients, major complications developing in 21 (5.3%) patients, and a 0% mortality rate.

Of the 19 minor complications, self-limiting hematuria occurred in six patients, postoperative pyrexia or pain in three patients, urinary tract infection treated with simple oral antibiotics in five patients, and minor intraoperative bleeding and postoperative urinary retention in one patient each.

Of the 21 major complications, Steinstrasse occurred in five patients, subcapsular hematoma in four patients, and obstructive pyelonephritis in four patients of which one went to the intensive care unit. The remaining three major complications were cerebrovascular accident, acute prostatitis, and hematuria causing clot retention in one patient each.

The average operative time was 82.5 minutes with a range of 28 to 215 minutes. The average stone size of the combined data was 2.5 cm. The combined use of ureteral access sheaths came to 86%. A subgroup analysis grouped into stones 2 to 3 cm and >3cm was also performed (Tables 3 and 4). There were 162 patients in the 2 to 3 cm stone group and 52 in the >3 cm group. It was evident that the success rate for FURSL for stones 2 to 3 cm was higher than for stones >3 cm with 95.7% vs 84.6% (P=0.01; odds ratio: 4.03; 95% confidence interval [CI]: 1.38–11.72) SFR, respectively. Furthermore, the 2 to 3 cm stone group had fewer procedures per patient (mean 1.46±0.2 vs 1.85±0.02 (P<0.0001; 95% CI: −0.42–0.36)). There were also fewer minor and major complications than the >3 cm group (14.3% vs 15.4%, and 0% vs 11.5%).

Methodologic quality assessment

Overall, the quality of the reported studies was poor, because six of the studies were reported as retrospective while two were unclear, although they seemed to be retrospective from the methodology. All the included studies may be subject to bias because they recruited patients from databases retrospectively; this could lead to selection as well as reporting bias. Some of the studies did not prospectively define the selection of patients for FURSL as opposed to PCNL.^5,7,12,13 The majority of the studies, however, mentioned that FURSL was attempted because of previous PCNL or SWL failure, patient preference after counseling, or if PCNL was contraindicated.^4,6,8,10,11 None of the studies was randomized or had a control group. Blinding was not an issue, because this is a surgical procedure and all groups will know the modality of treatment eventually. All the studies had clearly focused aims and used appropriate methodology to address those aims. There seemed to be no or little risk of classification bias because all the studies had the numbers accounted for, and all the patients had similar treatments.

The quality assessment of harms indicates that the studies generally have a low risk of bias concerning reporting the harms that could potentially be caused by the procedure (Table 5). The harms quality assessment could not be performed on one study because that study had not reported on any complications and did not mention an intention to do so.⁵

Table 5.

Quality Assessment of Harms

Author	Were the harms pre-defined using standardized or precise definitions?	Were serious events precisely defined?	Were devere events precisely defined?	Were the number of Deaths in the study group specified or were the reasons (s) for not specifying them given?	Was the mode of harms collection specified as active?	Was the mode of harms collection specified as passive?	Did the study specify Who collected the harms?	Did the study specify the training or background of who ascertained the harms?	Did the study specify the timing and frequency of who ascertained the harms?	Did the author(s) use standard scale(s) or checklist(s) for harms collection?	Did the authors specify if the harms reported encompass all the events collected or a selected sample?	Was the number of participants who withdrew or were lost to follow-up specified for each study group?	Did the authors specify the number for each type of harmful event?	Did the authors specify the type of analyses undertaken for harms data?
Grasso⁸	+	+	+	+	+	+	+	−	+	−	+	+	+	+
El-Anany¹²	+	+	−	+	+	−	+	−	+	−	+	+	+	+
Breda⁷	+	+	−	+	+	+	−	−	+	−	+	+	+	+
Riley⁶	+	+	−	+	+	+	−	−	+	−	+	+	+	+
Breda 2009¹¹	+	+	−	+	+	+	−	−	+	−	+	+	+	+
Bader¹⁰	+	+	−	+	+	+	+	+	+	−	+	+	+	+
Hyams¹³	+	+	−	+	+	+	+	+	+	−	+	+	+	+
Al-Qahtani⁴	+	+	−	+	+	+	+	+	+	−	+	+	+	+
Hussain⁵	+	+	−	+	+	+	+	−	+	−	+	+	+	+

Discussion

Principal findings

In this review, FURSL had an average SFR of around 93.7% (77%–97.5%) for a mean stone size of 2.5 cm, with an average of 1.6 procedures per patient and a mean operative time of 82.5 minutes. On a subgroup analysis, the SFR for stones between 2 and 3 cm was statistically significantly better than for stones >3 cm (95.7% vs 84.6%; P=0.01). Minor and major complications were seen in 4.8% and 5.3%, respectively.

Meaning of the study and comparison of FURSL in various studies (possible mechanism and implications for policy and practices)

Ureteroscopy and laser fragmentation of stone in the upper urinary tract has undergone development and refinement.^4,19

–22 Rigid ureteroscopy (URS) has been proven to be as efficient in stone clearance as SWL for proximal ureteral stones and superior in treating distal ureteral stones.^19,20

Harmon and coworkers²³ reported that because of the decrease in size of the ureteroscope, their complication rates for URS dropped from 6.6% to 1.5%. With advancements in ureteroscopic technology, the overall complication rates have decreased with major complication rates reported to be <1% to 1.5%. At the same time, the overall complication rates in PCNL have been reported to be as high as 83% with a 15% to 20% major complication rate.^{1,13,24
–26} FURSL has become the procedure of choice in patients in whom other modalities have failed and is a viable alternative for patients with obesity, anatomic deformity such as kyphoscoliosis, and in pregnancy.^4,7,10,22

The use of a ureteral access sheath facilitates easy passing of the ureteroscope, allows the removal of stone fragments, allows additive benefit of protecting the ureter from repeated insertion and removal of the scope, in addition to decreasing the intrarenal pressures during prolonged procedures by maintaining continuous drainage.^6,11 This review found that 86% of the FURSL procedures were ureteral sheath-assisted. It is worth noting that the two studies that did not use a ureteral access sheath were Grasso and associates⁸ and El-Anany and coworkers,¹² published in 1998 and in 2001 respectively, while the first article published on assessing ureteral access sheath use was in 2001.²⁸ Therefore, it is safe to say this technology was not readily available at the time these two studies were conducted.

None of the studies predefined the meaning of minor or major complications. The reviewing authors, however, considered minor complications as those that would settle on their own or with minimal support or a grade I of the Clavien-Dindo classification—ie, self-limiting hematuria or urinary tract infection necessitating antibiotics or analgesic²⁷—while major complications are those that needed either further procedures or close monitoring, classified as grade II or above of the Clavien-Dindo classification—ie, perforation, obstructive pyelonephritis, steinstrasse, or subcapsular hematoma.

Furthermore, a major discrepancy between the studies was the definition of the SFR. Two studies defined it as fragments <1 mm; however, the same lead author conducted both these studies.^7,11 The majority of the studies considered stone free as those 2 mm and below.^{4
–6,8,10,12} In addition, Hyams and associates¹³ subdivided the stone-free groups into those who are truly stone free, those who had a 0 to 2 mm retained fragment, and those with <4 mm retained fragment.

With regard to the subgroup analysis, although not all the studies were grouped for a meta-analysis, it is evident from the studies that FURSL has a high SFR in stones 2 to 3 cm compared with stones >3 cm. The SFR, however, decreased with the increase in stone size; furthermore, higher numbers of procedures were needed to achieve stone clearance with a rising risk of major complications.

Strengths and weaknesses of the study

The strength of the study remains the systematic approach taken to review the last 21 years of literature reporting on patients undergoing FURSL for large renal stones. The quality of the evidence was assessed using a validated instrument. Two independent researchers (not involved in any of the studies) performed data extraction to minimize potential for bias. Outcome parameters were predetermined and data were extracted using standard forms. An obvious weakness of all systematic reviews is that they depend on and reflect the evidence from the available primary studies and may not always be in a position to provide specific guidance on interventions as a result. The weaknesses of our conclusions are therefore closely linked to the weaknesses in the individual studies. These nonrandomized studies were potentially prone to large bias in patient selection, outcome assessment, and reporting.

Limitations and future areas of research

One of the limitations of this review was that all the included studies were retrospectively conducted. Full description of the methodology, however, was delineated in all the studies, which might be construed as lowering the risk of bias. Despite these limitations, all the studies had similar comparative parameters, which allowed for a meta-analysis of the data to formulate a more figurative result as well as a subgroup analysis. Another limitation is that the SFR was defined differently in studies. All the studies were from high-volume centers of excellence with procedures performed by trained experienced endourologists, and such high SFR may not be achievable in centers in which there is less experience.

Further research is vital to evaluate the role of URS and laser fragmentation of large urinary stones. Furthermore, a multicentric randomized trial comparing FURSL with PCNL for treatment of stones larger than 2 cm needs to be conducted. The parameters should ideally encompass operative times, number of procedures per patient, length of hospital stay, number of clinic or emergency department visits, SFRs, and complication rates. These parameters need to be explicitly defined. In addition to this, a cost analysis comparison between the two groups should also be performed. The complications should be classified into a known system, such as the Clavien-Dindo classification for surgical complications.²⁷

Conclusion

Although PCNL remains the gold standard, FURSL can successfully treat patients with stones larger than 2 cm with a high SFR and a low complication rate. The results of observational cohort studies, however, are from high-volume experienced centers and may not be sufficient to alter everyday routine practice; this review has shown that the efficacy of FURSL allows an alternative to PCNL. Because this high SFR may not be reproducible, an informed treatment decision should be made with the patients based on the outcomes for FURSL of the surgeons/centers.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

References

Mariani

. Combined electrohydraulic and holmium:YAG laser ureteroscopic nephrolithotripsy of large (greater than 4 cm) renal calculi. J Urol, 2007; 177:168–173.

Preminger

, Assimos

, Lingeman

et al. Chapter 1: AUA guideline on management of staghorn calculi: Diagnosis and treatment recommendations. J Urol, 2005; 173:1991–2000.

Wiesenthal

, Ghiculete

, D'A Honey

, Pace

. A comparison of treatment modalities for renal calculi between 100 and 300 mm²: Are shockwave lithotripsy, ureteroscopy, and percutaneous nephrolithotomy equivalent? J Endourol, 2011; 25:481–485.

Al-Qahtani

, Gil-Deiz-de-Medina

, Traxer

. Predictors of clinical outcomes of flexible ureterorenoscopy with holmium laser for renal stone greater than 2 cm. Adv Urol, 2012; 2012:543537.

Hussain

, Acher

, Penev

, Cynk

. Redefining the limits of flexible ureterorenoscopy. J Endourol, 2011; 25:45–49.

Riley

, Stearman

, Troxel

. Retrograde ureteroscopy for renal stones larger than 2.5 cm. J Endourol, 2009; 23:1395–1398.

Breda

, Ogunyemi

, Leppert

et al.

Flexible ureteroscopy and laser lithotripsy for single intrarenal stones 2 cm or greater—is this the new frontier?

J Urol, 2008; 179:981–984

Grasso

, Conlin

, Bagley

. Retrograde ureteropyeloscopic treatment of 2 cm. or greater upper urinary tract and minor Staghorn calculi. J Urol, 1998; 160:346–351.

Santaguida

P RP

, Ismaila

. McMaster Quality Assessment Scale of Hamrs (McHarm) for primary studies. hiru.mcmaster.ca/epc/mcharm.pdf. 2012 July 5.

10.

Bader

, Gratzke

, Walther

et al. Efficacy of retrograde ureteropyeloscopic holmium laser lithotripsy for intrarenal calculi >2 cm. Urol Res, 2010; 38:397–402.

11.

Breda

, Ogunyemi

, Leppert

, Schulam

. Flexible ureteroscopy and laser lithotripsy for multiple unilateral intrarenal stones. Eur Urol, 2009; 55:1190–1196.

12.

El-Anany

, Hammouda

, Maghraby

, Elakkad

. Retrograde ureteropyeloscopic holmium laser lithotripsy for large renal calculi. BJU Int, 2001; 88:850–853.

13.

Hyams

, Munver

, Bird

et al. Flexible ureterorenoscopy and holmium laser lithotripsy for the management of renal stone burdens that measure 2 to 3 cm: A multi-institutional experience. J Endourol, 2010; 24:1583–1588.

14.

Mariani

. Combined electrohydraulic and holmium:yag laser ureteroscopic nephrolithotripsy for 20 to 40 mm renal calculi. J Urol, 2004; 172:170–174.

15.

Mariani

. Combined electrohydraulic and holmium:YAG laser ureteroscopic nephrolithotripsy of large (>2 cm) renal calculi. Indian J Urol, 2008; 24:521–525.

16.

Ricchiuti

, Smaldone

, Jacobs

et al. Staged retrograde endoscopic lithotripsy as alternative to PCNL in select patients with large renal calculi. J Endourol, 2007; 21:1421–1424.

17.

Chu

, Sternberg

, Averch

. Preoperative stenting decreases operative time and reoperative rates of ureteroscopy. J Endourol, 2011; 25:751–754.

18.

Hyams

, Shah

. Percutaneous nephrostolithotomy versus flexible ureteroscopy/holmium laser lithotripsy: Cost and outcome analysis. J Urol, 2009; 182:1012–1017.

19.

Preminger

, Tiselius

, Assimos

et al. 2007 Guideline for the management of ureteral calculi. Eur Urol, 2007; 52:1610–1631.

20.

Tiselius

, Ackermann

, Alken

et al. Guidelines on urolithiasis. Eur Urol, 2001; 40:362–371.

21.

Galvin

, Pearle

. The contemporary management of renal and ureteric calculi. BJU Int, 2006; 98:1283–1288.

22.

Grasso

, Beaghler

, Bagley

, Strup

. Actively deflectable, flexible cystoscopes: No longer solely a diagnostic instrument. J Endourol, 1993; 7:527–530.

23.

Harmon

, Sershon

, Blute

et al. Ureteroscopy: Current practice and long-term complications. J Urol, 1997; 157:28–32.

24.

Turna

, Stein

, Smaldone

et al. Safety and efficacy of flexible ureterorenoscopy and holmium:YAG lithotripsy for intrarenal stones in anticoagulated cases. J Urol, 2008; 179:1415–1419.

25.

Watterson

, Girvan

, Cook

et al. Safety and efficacy of holmium:YAG laser lithotripsy in patients with bleeding diatheses. J Urol, 2002; 168:442–445.

26.

Michel

, Trojan

, Rassweiler

. Complications in percutaneous nephrolithotomy. Eur Urol, 2007; 51:899–906.

27.

Dindo

, Demartines

, Clavien

. Classification of surgical complications: A new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg, 2004; 240:205–213.

28.

Kourambas

, Byrne

, Preminger

. Does a ureteral access sheath facilitate ureteroscopy? J Urol, 2001; 165:789–793.