Redefining the Limits of Flexible Ureterorenoscopy

Abstract

Background and Purpose:

Flexible ureterorenoscopic holmium laser lithotripsy allows retrograde management of renal calculi that previously needed alternative strategies. This study assesses the influences of stone size, density, and location on treatment outcomes from a large series.

Patients and Methods:

Data concerning patients who presented for ureterorenoscopic laser lithotripsy between May 2005 and September 2008 were retrospectively analyzed. Single-treatment success was defined as satisfactory visual clearance of stone bulk, radiopacities less than 2 mm on noncontrast CT, and no further treatment.

Results:

One hundred and eighty-five patients had 236 treatments (median = 51 years; range 18–83 years). Overall success rate was 90.7%. The mean ± standard deviation (SD) stone size was 13.1 ± 8.5 mm with significant differences between the successful (11.6 ± 6.7 mm) and nonsuccessful (27.8 ± 10.0 mm) outcome groups (P < 0.0001, unpaired t test). Of treatments for stone size ≤20 mm, 96.5% were successful. Of 36 patients with stone size >20 mm, 21 (58.3%) were stone free after one treatment and 31 (86.1%) after two treatments. Hounsfield unit data did not differ significantly between the groups (mean ± SD 858 ± 388 vs 1115 ± 643, P = 0.146, unpaired t test). Stone locations were: Renal pelvis, caliceal diverticula, and upper pole, midpolar, and lower pole in 61, 9, 24, 27, and 115 cases with success rates of 85%, 100%, 83%, 93%, and 94%, respectively (P = 0.899, chi-square test).

Conclusion:

Clearance rates of >90% can be achieved for stones up to 20 mm with flexible ureterorenoscopy and holmium laser lithotripsy, but with larger stones, the stone-free rates reduce significantly. Therefore, 20 mm should be regarded as the upper limit of stone size that can be cleared in a single procedure. Stone density and location do not influence outcome.

Introduction

T he visualization of a ureteral stone with a flexible ureterorenoscope was first described by Marshall¹ in 1964. Subsequently, there have been major advances in the design and development of these instruments, with the availability of flexible ureterorenoscopes that have active two-way deflection along with secondary passive deflection, making the entire upper tract accessible to the endourologist.

The management of renal calculi is outlined by the European Association of Urology (EAU). Its current guidelines recommend extracorporeal shockwave lithotripsy (SWL) and percutaneous nephrolithotomy (PCNL) as primary treatment options.² Although SWL is minimally invasive, there are several described complications, including obstruction and urinary tract infection, and it is unsuitable for some patients—for example, in pregnancy, morbid obesity, renal artery or aortic aneurysmal disease, coagulopathy, and sepsis.³ Furthermore, success rates are variable, particularly for lower pole stones,^3,4 and hard stones, such as calcium oxalate monohydrate and cystine stones.⁵

For larger renal calculi, PCNL achieves success rates of up to 95%.⁶ PCNL is a surgical procedure that has potentially serious risks, including pleural injury (up to 3.1% overall or 10% if punctured above the 12th rib) and hemorrhage necessitating blood transfusion (11.2%–17.5%).⁷ It may not be suitable for patients with anatomic abnormalities, morbid obesity, or clotting disorders.⁸ Renal insufficiency and pulmonary disease may also increase the risk of complications of PCNL, and length of inpatient stay after this procedure is longer than that of other treatment modalities.⁷

The use of flexible ureterorenoscopy (URS) and laser lithotripsy may be an alternative to SWL and PCNL. EAU guidelines state that flexible URS has not been recommended as a first-line treatment for renal calculi, and there are no valid data to support such a recommendation.² Because using SWL for lower pole stones has poor results, flexible URS could become a reliable first-line treatment for lower pole stones <15 mm. ² Joint guidelines from the EAU and American Urological Association, however, state that for patients who need stone removal, both SWL and URS are acceptable first-line treatments,⁹ although this is based on ureteral calculi.

We present our series of flexible URS with respect to stone-free outcome, to our knowledge the largest to date. The purpose of this study was to investigate factors that influence the outcomes of flexible URS holmium laser lithotripsy for the management of renal calculi, including stone size, position, and density. We further stratified the efficacy of treatment by stone burden ≤20 mm and >20 mm.

Patients and Methods

Patients

All patients who presented for intended flexible URS and holmium laser lithotripsy for renal calculi between May 2005 and September 2008 were studied retrospectively. There were no exclusion criteria. Data concerning patient demographics, stone size, stone location, and stone density according to maximum Hounsfield unit on CT were prospectively collected and recorded onto a database. Patients were grouped according to both their stone size and stone location.

Patients had a standard preoperative assessment and counseling regarding alternative management options and the possibility of further laser lithotripsy sessions or adjuvant treatments with SWL or PCNL. All patients gave written informed consent and were told in particular about ureteral stents and stent symptoms.

Technique

All procedures were performed under general anesthesia and by a single endourology-trained surgeon or under supervision by this surgeon. In all cases, retrograde access to the upper urinary tract was obtained over a safety guidewire with an 8.3F flexible ureterorenosope (Olympus Keymed, Southend, UK) under fluoroscopic guidance (single Olympus P3 flexible ureteroscope was used until mid-2006, followed by a single Olympus P5 flexible ureteroscope). A holmium laser using a 200 μm or 365 μm fiber was used for lithotripsy at 0.5 to 1.0 J at a pulse rate of 5 to 10 Hz. Ureteral access sheaths (Cook Medical, Bloomington, IN) and ureteral Nottingham dilators (Boston Scientific, Natick, MA) were used if access was found to be difficult. The aim was to completely ablate the calculi or reduce the calculi to fragments <2 mm to allow for spontaneous passage. For a few patients, a ureteral double pigtail stent (Vortek, Porges, France) was inserted until further treatment had been agreed. Patients were routinely discharged within 23 hours of treatment.

Data collection

The parameters recorded were: Stone size—largest dimension on plain radiography/CT; density—Hounsfield unit on CT; and stone location—pelvis, caliceal, upper pole, midpolar, lower pole. Successful treatment was identified by satisfying all three of the following criteria: Satisfactory visual clearance of stone bulk at the time of URS, radiopacities <2 mm on noncontrast CT, and no need for further treatment within 6 months. This study was approved as a retrospective study by the local ethics committee.

Statistical methods

Unpaired t tests and the chi-square test were used for statistical analysis using the Predictive Analytics SoftWare Statistics version 18.0. P < 0.01 was used to distinguish the level of significance.

Results

One hundred and eighty-five patients (103 males, 82 females), with a median age of 51 years (range 18–83 y), with renal calculi underwent 236 treatments for renal calculi using flexible ureterorenoscopic holmium laser lithotripsy.

Stone clearance was obtained with a single treatment alone in 214 (90.7%) of treatments (Table 1). There was a significant difference between the successful and nonsuccessful outcome groups with respect to stone size (Tables 1 and 2). Figure 1 displays single treatment success vs stone size. Of treatments for stone size ≤20 mm, 96.5% were successful. Of 36 patients with stone size >20 mm, 21 (58.3%) were stone free after one treatment, 31 (86.1%) after two, 32 (88.9%) after three, and 34 (94.4%) after four. One patient needed PCNL, and one was lost to follow-up.

FIG. 1.

Single treatment success vs stone size.

Table 1.

Success Rates Comparing Stone Size and Stone Density

	Single treatment success	>1 treatment needed	Total number of treatments	P value
n (%)	214 (90.7)	22 (0.3)	236	-
Mean (±SD) stone size (mm)	11.6 ± 6.7	27.8 (±10.0)	13.1 (±8.5)	<0.0001
Mean (±SD) Hounsfield unit	858 (±388)	1115 (±643)	913 (±462)	0.146

SD = standard deviation.

Table 2.

Success Rates Comparing Stone Size

Stone size	Successful	%	Unsuccessful	%	Total
<5 mm	29	100	0	0	29
5–10 mm	77	100	0	0	77
11–15 mm	58	98.3	1	1.7	59
16–20 mm	29	82.9	6	17.1	35
21–30 mm	17	70.8	7	29.2	24
>30 mm	4	33.3	8	66.7	12
Total	214	90.7	22	9.3	236

Hounsfield unit data did not differ significantly between the groups (Table 1), and stone location did not influence success (P = 0.899, chi-square test) (Table 3). Of 115 lower pole stones, 108 (93.9%) had successful single session treatment. Further detailed data outlining treatment success with respect to stone location and stone size are displayed in Table 4. Ureteral stent insertion was necessary in 170 (72.0%) treatments. Six patients (20.7% of total patients with calculi <5 mm) needed ureteral stent insertion after treatment for calculi <5 mm, 51 (66.2%) patients for calculi between 5 and 10 mm, 47 (79.7%) for 11 to 15 mm, 32 (91.4%) for 16 to 20 mm, 23 (95.8%) for 21 to 30 mm, and 11 (91.67%) patients needed stent insertion after treatment for calculi >30 mm.

Table 3.

Success Rates Comparing Stone Location

Stone location	Successful	%	Unsuccessful	%	Total
Lower pole	108	93.9	7	6.1	115
Midpolar	25	92.6	2	7.4	27
Upper pole	20	83.3	4	16.7	24
Caliceal diverticulum	9	100	0	0	9
Renal pelvis	52	85.2	9	14.7	61
Total	214	90.7	22	9.3	236

Table 4.

Treatment Success with Respect to Stone Location and Stone Size

	Stone Size
	Successful/Unsuccessful
Stone Location	<5 mm (%)		5–10 mm (%)		11–15 mm (%)		16–20 mm (%)		21–30 mm (%)		>30 mm (%)		Total
Lower pole	14 (5.9)	0 (0.0)	40 (16.9)	0 (0.0)	31 (13.1)	1 (0.4)	15 (6.4)	1 (0.4)	8 (3.4)	2 (0.8)	0 (0.0)	3 (1.3)	115 (48.7)
Midpolar	6 (2.5)	0 (0.0)	9 (3.8)	0 (0.0)	4 (1.7)	0 (0.0)	3 (1.3)	2 (0.8)	1 (0.4)	0 (0.0)	2 (0.8)	0 (0.0)	27 (11.4)
Upper pole	6 (2.5)	0 (0.0)	7 (3.0)	0 (0.0)	1 (0.4)	0 (0.0)	3 (1.3)	1 (0.4)	3 (1.3)	1 (0.4)	0 (0.0)	2 (0.8)	24 (10.2)
Caliceal diverticulum	3 (1.3)	0 (0.0)	3 (1.3)	0 (0.0)	3 (1.3)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	9 (3.8)
Renal pelvis	0 (0.0)	0 (0.0)	18 (7.6)	0 (0.0)	19 (8.1)	0 (0.0)	8 (3.4)	2 (0.8)	5 (2.1)	4 (1.7)	2 (0.8)	3 (1.3)	61 (25.8)
Total	29 (12.3)	0 (0.0)	77 (32.6)	0 (0.0)	58 (24.6)	1 (0.4)	29 (12.3)	6 (2.5)	17 (7.2)	7 (3.0)	4 (1.7)	8 (3.4)	236 (100)

The most common cause for unsuccessful treatment was excessive stone bulk, accounting for 18 of 22 unsuccessful treatments. A ureteral access sheath was used in eight (3.4%) patients for difficult access at the lower ureter. Access sheath placement was routinely preceded by dilation. There was failed access on two (0.8%) occasions because of relative stenosis at the lower ureter, the laser was unable to reach the stone on one (0.4%) occasion, and one (0.4%) patient was lost to follow-up.

Discussion

This study shows that flexible URS and laser stone fragmentation is an effective first-line treatment modality for renal calculi, with an overall single session success rate of 90.7%, and is not influenced by stone location and density. These data are comparable to other series with success rates of 65% to 79%.^10
–12 Cocuzza and associates¹³ found that treatment failure of a single session was associated with presence of a stone >15 mm.¹³ In our opinion, flexible URS is most effective for stones ≤20 mm, with a 96.5% success rate. Other centers have reported stone-free rates for calculi ≤20 mm ranging from 58% to 95%.^14,15 Clearance of stones larger than this size takes multiple attempts. The proportion of patients free from calculi after SWL varies from 35% to 91%, depending on size and location, and between 60% and 100% of cases for renal calculi >2 cm are eliminated with PCNL.¹⁶

We obtained a success rate of 58.3% for renal calculi >20 mm with a single treatment, 86.1% after two treatments, and 88.9% after three treatments, based on our criteria for success. These results can be compared with Breda and colleagues,¹⁷ who achieved success rates of 60%, 86.6%, and 93.3%, respectively. A stone-free rate of 77% for a renal stone burden >2 cm treated with URS and laser lithotripsy has also been described, with minor complications of hematuria and fever.¹⁸ Stone-free rates of 91% have been described for renal stones >2.5 cm with planned URS.¹⁹ Mariani²⁰ has also reported stone-free status in 88% of patients with renal calculi >4 cm. Flexible URS has not been recommended as first-line treatment of renal calculi, however, but as a reserve for SWL-refractory renal calculi.²

For management of large renal calculi, flexible URS and laser lithotripsy have been shown to be an alternative to PCNL, although multiple procedures may be necessary. For stones >2 cm, patients underwent an average of 1.4 procedures to become stone free and a mean of 2.3 including the final diagnostic URS and stent removal.¹⁷ Operative time favors URS, and patients reported increased satisfaction with short-stay procedures, because there is no missed time from work or other activities.¹⁷ Stent symptoms after URS, which include irritative bladder symptoms and pain,²¹ may be significant, and these need to be balanced with the risks of morbidity with PCNL.⁷ Combination treatment of flexible URS with SWL or PCNL has also been reported to improve stone-free rates.²² Hyams and Shah²³ have reported that for 2 to 3 cm stones, one-stage URS may be a viable option compared with PCNL, depending on stone burden and location. They also found that the estimated cost of PCNL treatment was significantly greater than that of URS ($19,845 vs $6,675, P < 0.0001), estimated from local New York Medicare reimbursement scales.²³

In this series, there was no statistically significant difference in results between renal calculi in different locations. We have shown that flexible URS can also be used to manage stones in caliceal diverticula. Using holmium laser lithotripsy, a treatment success rate of 92% has been described for lower pole stones,¹³ comparable to 93.9% in our study. Comparative data are not available on stone-free rates for renal calculi in different intrarenal locations using flexible URS and holmium laser lithotripsy. No relationship between stone density and success rate has been identified in our study. Bandi and coworkers²⁴ did show that stone volume, as opposed to stone density, was the strongest predictor of stone-free status after SWL. A Hounsfield unit <900, however, has been shown to predict SWL success.²⁵ It must be noted that the energy at which the holmium laser fragments calculi can be increased if the stones are hard and resisting fragmentation.

Our study has several limitations. It is a single-center study, which would need to be repeated in other centers to obtain more data and compare stone-free rates. We also did not look at operative time and postoperative complications. We have found that patients with a stone size >20 mm can be successfully treated but may need more than one treatment session. One hundred and seventy (72.0%) patients did need ureteral stent placement, and therefore at least one further procedure to remove this stent. We also did not look at the time to stone and stent free, which may favor use of PCNL for larger stones. Because holmium laser lithotripsy is minimally invasive, some clinicians believe that ureteral stent placement and postoperative upper tract imaging are no longer needed in uncomplicated cases.^21,26 The holmium laser also has the advantage of stone ablation as well as fragmentation, so less stone debris that needs to pass. This leads to avoidance of ureteral stent placement for smaller stones.

Equipment availability and surgical experience play an important role in success rates for single treatment flexible URS and laser stone fragmentation. Recent technologic advances in the design of ureterorenoscopes and laser fibers allow endourologists to manage renal calculi by retrograde URS. Electrohydraulic lithotripsy is the only other treatment modality with a flexible delivery system, with success rates ranging from 63.3%²⁷ to 90.3%.²⁸

Our data support the use of ureterorenoscopic treatment of patients with renal calculi of varying stone sizes. All patients with renal calculi must be appropriately counseled about the risks and benefits of ureterorenoscopic treatments and the alternatives of SWL and PCNL. Ultimately, patient choice influences treatment decisions, with each available treatment modality having its own benefits and risks. A randomized, controlled trial comparing flexible URS and laser lithotripsy with SWL and PCNL is warranted to further evaluate the role of flexible URS when advising patients regarding treatment for renal tract calculi.

Conclusions

Our prospective experience of flexible URS and holmium laser lithotripsy has shown it to be a reliable first-line treatment for renal calculi. Clearance rates of >90% can be achieved for stones up to 20 mm with flexible URS and holmium laser lithotripsy, but with larger stones the stone-free rates reduce significantly. Therefore, 20 mm should be regarded as the upper limit of stone size that can be cleared in a single procedure. Successful clearance is not influenced by stone density or position. Although currently, PCNL remains the gold standard treatment for large intrarenal stones, URS and laser lithotripsy allow a minimally invasive alternative with the proviso that more than one session may be needed. As an efficient energy source with a flexible delivery system, it is the holmium laser, which enables high stone-free rates.

Patients must be counseled appropriately with regard to all available treatment modalities and must balance the pros and cons of possible stent symptoms with further treatments and a shorter stay.

Footnotes

Disclosure Statement

No competing financial interests exist. Mark Cynk is a Managing Director of Kent Mobile Medical Limited, which owns a holmium laser. The authors are employed by the National Health Service (UK).

Abbreviations Used

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