REVIEWS Pushing the boundaries of ureteroscopy: current status and future perspectives Petrisor Geavlete, Razvan Multescu and Bogdan Geavlete Abstract | Substantial advances in ureteroscopy have resulted in the incorporation of this procedure into routine urological practice in many centres worldwide. Subsequently, an abundance of clinical data and technological progression have enabled the development of novel solutions that have increased the efficacy of ureteroscopy, and reduced associated morbidity and costs. In addition the indications for this retrograde approach have been expanded, and pyelocalyceal diverticulum, infundibular stenosis, urolithiasis in pregnant women or in patients with urinary diversions, as well as upper urinary tract tumours can now be managed using this methodology. New endoscopes are continuously developed, with different manufacturers choosing various technical solutions to further increase the efficacy and safety—and sometimes decrease costs—of ureteroscopy, including miniaturization, inclusion of digital optical systems and dual working channels, and the introduction of disposable apparatus. The holmium laser, currently the most-versatile energy source available, enables tissue incision, tumour ablation, and intracorporeal lithotripsy. Modern ancillary instruments are diverse, flexible, and durable, and novel devices used in daily clinical practice can minimize ascendant migration of stone fragments and, therefore, decrease the failure rate of the retrograde ureteroscopic approach. However, the peak of ureteroscopy evolution seems to remain distant, with further improvement of endoscopes and ancillary instruments, and robot-assisted ureteroscopy representing only some of the areas in which future developments are possible. Geavlete, P. et al. Nat. Rev. Urol. 11, 373–382 (2014); published online 3 June 2014; doi:10.1038/nrurol.2014.118
Introduction
Urological Department, Saint John Emergency Clinical Hospital, Vitan Barzesti 13, Bucharest 042122, Romania (P.G., R.M., B.G.). Correspondence to: P.G. [email protected]
The past decades have witnessed dramatic changes in ureteroscopy, which has led to this methodology becoming a routine procedure in many urological clinics worldwide, especially for the treatment of urolithiasis and in the diagnosis of upper urinary tract pathology. The adoption of ureteroscopic procedures into the daily management of these conditions has resulted in enormous quantities of clinical data. Together with technological progression, this wealth of clinical experience has driven the development of novel solutions to expand the indications and increase the efficacy of the upper urinary tract endoscopic retrograde approach, and decrease associated morbidity and costs. Of note, ureteroscopic urolithotripsy is now feasible in pregnant women or in patients with urinary diversions, and pyelocalyceal diverticulum, infundibular stenosis, and upper urinary tract tumours can also be managed using this methodology. In particular, miniaturization, the addition of digital optical systems and second working channels to ureteroscopes, and the introduction of disposable apparatus represent key advances in the utility of this methodology. In parallel, the introduction of holmium lasers has enabled effective and accurate tissue incision, tumour ablation, and intracorporeal lithotripsy, Competing interests B.G. declares that he is a member of the speakers’ bureau and has received honouraria from Olympus. The other authors declare no competing interests.
and modern ancillary tools can be used, for example, to minimize ascendant migration of stone fragments. Importantly, the evolution of ureteroscopy is ongoing, with multiple manufacturers finding different technical solutions to further increase the performance and versatility of endoscopes and ancillary instruments. Such developments, as well as advances in robot-assisted procedures, hold great promise in improving the efficacy and safety of ureteroscopy and, therefore, the management of urological conditions. In a review published in 2008, Holden et al.1 stated that “endourology could be redefined as ‘enginurology’, as the marriage between engineering and urology”; this postulate is probably more appropriate for ureteroscopy than any other procedure. Herein, we review the current status of ureteroscopy, focusing on the technical advances that have been made to date. In addition, we highlight how these developments and continued efforts to adapt and improve ureteroscopy apparatus and protocols could increase the effectiveness and broaden the utility of the endoscopic retrograde approach in the future.
New-generation ureteroscopes Current rigid and semirigid ureteroscopes Initially developed as an extension of cystoscopy, uretero scopy has become a key technique in the diagnosis and treatment of a number of urological conditions. The first ureteroscopes, introduced in the late 1970s, were rigid or
NATURE REVIEWS | UROLOGY
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REVIEWS Key points ■■ Ureteroscopy is a routine procedure used in the treatment of conditions such as urolithiasis and in the diagnosis of upper urinary tract pathology in many centres worldwide ■■ Ureteroscopy with flexible endoscopes, in particular, is important in the resolution of various pathological events, such as pyelocalyceal lithiasis, migrated stone fragments, pyelocalyceal diverticulum, and renal infundibular stenosis ■■ New semirigid and flexible endoscopes designed for ureteroscopy, with either fibre-optic or digital optical imaging systems, are continuously being improved and developed ■■ The holmium laser is the most-efficient and most-versatile energy source used in ureteroscopy procedures, enabling tissue incision, tumour ablation or intracorporeal lithotripsy ■■ In addition, novel accessory devices are being incorporated into routine clinical ureteroscopy procedures to minimize retropulsion and ascendant migration of stone fragments
semirigid, and were shorter, thicker and more cumbersome than the current instruments; therefore, the use of these instruments was limited to the management of a small numbers of lesions of the distal ureter. In the subsequent decades, rigid and semirigid ureteroscopes were continuously refined, becoming longer and thinner, and enabled access to the proximal ureter and parts of the pyelocalyceal system. However, the maximum potential for development of rigid and semirigid ureteroscopes aimed at improving the management of urological conditions was seemingly reached some time ago. In fact, the develop ment of semirigid ureteroscopes with digital imaging systems (rather than fibre-optic imaging systems), such as the EndoEye video ureteroscope (Olympus Europe, Germany), might be considered the only major technological achievement made with regard to rigid or semirigid ureteroscopy during the past two decades.2 Nevertheless, miniaturization has also been a key focus in the development of semirigid ureteroscopes; The Needle ureteroscope
(Richard Wolf, Germany) has a tip diameter of only 4.5F and a shaft diameter of 6.5F, and is suitable for use in paediatric or adolescent patients. Technical parameters of these and some of the other commercially available models of semirigid ureteroscopes are summarized in Table 1.
The development of flexible ureteroscopes Improved imaging In comparison with the apparent plateau in the development of rigid and semirigid ureteroscopy platforms, the advancement of flexible ureteroscopy instrumentation is still in a period of continuous evolution. First developed during the 1980s by Bagley and colleagues,3 flexible ureteroscopes have the major advantage of being able to reach, at least theoretically, the entire upper urinary tract using the anatomical passages of the urinary system. However, the performance and utility of such apparatus were limited for a prolonged period of time by poor visi bility and sometimes impaired manoeuvrability in use, as well as their fragility and high cost in comparison with the semirigid ureteroscopes that were available during the same period. Over the past decade, the development of flexible ureteroscopes with digital optical systems has largely solved the visibility issue, with modern models such as the Flex-Xc (KARL STORZ Endoskope, Germany) or the URF‑V (Olympus Europe, Germany) generally providing an endoscopic field of view that is larger and clearer compared with fibre-optic models (Figure 1), and sometimes even semirigid apparatus from the same manufacturers. Differences between these two models of flexible video ureteroscopes exist: the Flex-Xc is thinner at the tip and highly manoeuvrable, with a greater upwards deflection angle (270° versus 180°; Table 2), whereas the URF‑V has a larger diameter (Figure 2), which creates some potential access problems in the narrow segments of the upper urinary tract; however, the latter model offers a larger
Table 1 | Technical characteristics of selected semirigid ureteroscopes Manufacturer and model
Number and diameter of channels
Tip diameter
Outer diameter
Length of shaft
Optical system
OES Pro
Single: 4.2F
6.4F
7.8F
33 cm or 43 cm
Fibre-optic
OES Pro
Single: 6.4F
8.6F
9.8F
43 cm
Fibre-optic
OES 4,000
Dual: 2.4F and 3.4F
NA
7.5F
43 cm
Fibre-optic
EndoEye video ureteroscope
Single: 4.2F
8.5F
9.9F
43 cm
Digital (CCD)
The Needle
Single: 3F
4.5F
6.5F
31.5 cm or 43 cm
Fibre-optic
The Ultrathin
Single: 4F
6F
7.5F
33 cm or 43 cm
Fibre-optic
The D.O.C.
Dual: 4F and 2.4F
6.5F
8.5F
33 cm or 43 cm
Fibre-optic
Olympus (Germany)
Richard Wolf (Germany)
KARL STORZ Endoskope (Germany) MICHEL Uretero-Renoscope
Dual: 3F and 2.3F*
9F
9.5F or 12F
43 cm
Fibre-optic
Uretero-Renoscope
Single: 4.8F
6.5F
7F or 9.9F
34 cm or 43 cm
Fibre-optic
Uretero-Renoscope
Single: 5F
7F
8F or 12F
34 cm or 43 cm
Fibre-optic
Uretero-Renoscope
Single: 6F
8F
9.5F or 12F
34 cm or 43 cm
Fibre-optic
Uretero-Renoscope
Dual: 3.4F and 2.4F*
7F
7F or 8.4–9.9F
34 cm or 43 cm
Fibre-optic
*The smaller channel in these apparatus can only be used for irrigation purposes. Abbreviations: CCD, charged-coupled device; NA, data not available.
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REVIEWS a
(the tumour-detection rate was unchanged in the other patients assessed).5 However, authors of this study conclude that, in their opinion, the NBI-based procedure for detection of urothelial tumours they describe cannot be recommended for use in daily practice at present.5 Further validation of the technique is, therefore, required.
b
Figure 1 | Comparison of the current imaging capabilities of flexible ureteroscopes. The two images shown demonstrate the differences in image resolution between a | the fibre-optic Richard Wolf Cobra flexible ureteroscope and b | a Olympus URF‑V device with a digital optical system. At present, the image quality obtained with fibreoptic ureteroscopes cannot match the quality of those with digital imaging capability.
endoscopic field of view and is the only flexible ureteroscope with narrow-band imaging (NBI) capabilities.4 NBI is an optical image-enhancement technology that, unlike white-light imaging, relies on emission of two specific wavelengths of light with high absorbance by haemo globin: blue light of 415 nm, which penetrates the superficial layers of the mucosa and causes vessels within this tissue to appear brown; and 540 nm green light, which has greater tissue penetration and makes deeper vessels appear cyan. Thus, NBI increases the visibility of blood vessels and other structures within the urothelium, and the main purpose of this technology is to improve tumour detection. In this context, the first clinical experience of NBI demonstrated the promise of this approach, as the upper urinary tract urothelial tumour-detection rate was improved by 22.7% among in seven (25.9%) of 27 patients studied, compared with conventional white-light ureteroscopy
Miniaturization Although the digital flexible ureteroscopes now provide a good level of visibility, attempts to further miniaturize apparatus are ongoing. One of the latest models of conventional flexible ureteroscope, the URF‑P6/P6R (Olympus Europe, Germany), has the advantage of a super-slim design with a maximal outer-shaft diameter of 7.95F and a tip diameter of only 4.9F (Table 2). The small diameter of this instrument, together with the incorporation of a stiffer shaft than other flexible scopes currently available, can simplify insertion of the ureteroscope and improve access ibility to the upper urinary tract. As the URF‑P6/P6R uses a fibre-optic imaging system, this instrument cannot match the performance of current digital video ureteroscopes with regard to visibility;4,6 however, the URF‑P6/ P6R uses a moiré filter to enhance imaging accuracy in an attempt to at least partially solve this problem. Incorporation of dual working channels The manufacturer of the Cobra flexible ureteroscope (Richard Wolf, Germany) chose a different approach to improving visibility during ureteroscopy procedures: the addition of a second working channel (Figure 3; Table 2). This modification enables unimpaired irrigation flow and the simultaneous use of ancillary instruments, therefore, providing a clearer field of view than is possible with single-channel ureteroscopes that often suffer from severe loss or even interruption of irrigation when ancillary instruments are in use.7 More importantly, the inclusion of
Table 2 | Technical characteristics of selected flexible ureteroscopes Manufacturer and model
Number and diameter of channels
Tip diameter
Outer diameter
Length of shaft
Optical system
Maximum deflection (down/up)
URF‑V
Single: 3.6F
8.5F
9.9F
67 cm
Digital
275o/180o
URF‑P5
Single: 3.6F
5.3F
8.4F
70 cm
Fibre-optic
275o/180o
URF‑P6
Single: 3.6F
4.9F
7.95F
67 cm
Fibre-optic
275o/275o
Viper
Single: 3.6F
6F
8.8F
68 cm
Fibre-optic
270o/270o
Cobra
Dual: both 3.3F
6F
9.9F
68 cm
Fibre-optic
270o/270o
Olympus (Germany)
Richard Wolf (Germany)
KARL STORZ Endoskope (Germany) Flex‑X2
Single: 3.6F
7.5F
8.4F
67 cm
Fibre-optic
270o/270o
Flex-Xc
Single: 3.6F
7.8F
8.5F
70 cm
Digital
270o/270o
Single: 3.5F
8F
8F
85 cm
Fibre-optic
180o*
SemiFlex™ Endo55
Single: 3.4F
6.4F
7.85F
55 cm
Fibre-optic
210o/210o
SemiFlex™ Endo65
Single: 3.4F
6.4F
7.85F
65 cm
Fibre-optic
210o/210o
Lumenis (Israel) PolyScope MaxiFlex (USA)
*180 single direction deflection but the instrument can be rotated 360 . o
o
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b
Figure 2 | Olympus URF‑V (top) and KARL STORZ Endoskope Flex-Xc (bottom) ureteroscopes. a | Photograph of the ureteroscopes bodies demonstrating the control modules. b | Photograph showing the distal working parts of these flexible ureteroscopes at maximum downwards deflection (275o and 270o, respectively). Both of these devices are fitted with digital optical systems. The instruments also both have a single channel of the same diameter (3.6F), although the URF‑V instrument is clearly slightly larger than the Flex‑Xc model, with outer diameter of 9.9F versus 8.5F (tip diameters of 8.5F and 7.8F respectively).
a
b
Figure 3 | The Richard Wolf Cobra, the first dual channel flexible ureteroscope. a | Photograph showing the proximal parts of the device, in which the entry points to the two channels within the endoscope are visible, as is the eyepiece for the fibre-optic imaging device. The inclusion of two 3.3F channels enables laser fibres up to a maximum of 365 μm to be accommodated in a separate working channel that incorporates a ‘laser shifter’ for better control, which together might improve the precision, and reduce the damage to tissues and the instrument itself caused by the laser. b | This image shows details of the tip of the device at maximum deflection; this instrument has the same upwards and downwards deflection of 270o, and has outer and tip diameters of 9.9F and 6F, respectively.
dual working channels enables simultaneous insertion of ancillary instruments in different combinations, thus creating new procedural opportunities.7 Improved durability Improvements have reduced the previous fragility dis advantage of flexible ureteroscopes compared with semirigid and rigid models; the durability of the new flexible endoscopes seems to be superior to the older flexible ureteroscopes, ultimately translating into reduced interventional costs.8 A paper reported the use of the Flex-Xc model for a mean number of 135 procedures per ureteroscope, and one uretersocope was used for 159 procedures before major repairs were needed.9 By comparison, published experience with older flexible ureteroscopes, such as the DUR 8 or DUR 8‑Elite models (ACMI Corporation, USA; now part of Olympus), 11274AA (KARL STORZ Endoskope, Germany), 7325.172‑7.5F or 7330.072‑9.0F (Richard Wolf, Germany) and URF‑P3 (Olympus Europe, Germany), indicated that only 10 to 34 procedures were possible before breakages occurred.10 376 | JULY 2014 | VOLUME 11
Disposable flexible ureteroscopes The PolyScope (Lumenis, Israel), a disposable flexible ureteroscope composed of a single-use flexible catheter and a reusable fibre-optic bundle, was developed with the main aim of decreasing costs associated with ureteros copy (Table 2). The multilumen disposable catheters used with this device are relatively cheap in comparison with reusable ureteroscopes, preclude the requirement for sterilization of the ureteroscope shaft, thus minimizing the risk of instrument-related infection, and simplify sterilization of the optical cable, reducing the chances of procedural and postprocedural damage to the imaging system that is a frequent occurrence with other models of multiuse flexible ureteroscopes.11 Initial data on the clinical use of the PolyScope indicate that the instrument is safe, convenient, and effective for the lithotripsy of upper urinary tract calculi and, therefore, confirm the theoretical promise attributed to disposable ureteroscopes.11 With regard to technical performance, the optical system used in the PolyScope provides 10,000 pixels resolution, enabling the visualization of targets 0.125 mm in size within a range of 2–4 mm without moiré effect, and has a 3.6F working channel, similar to that of most reusable flexible ureteroscopes.12 Although cheaper to buy and less costly to use repeatedly, this disposable apparatus does not solve the manoeuvrability issues associated with other flexible ureteroscopes and is similarly fragile.12 However, the PolyScope can also be used as a rigid or semirigid ureteroscope if necessary, by inserting it through ChiRiFlex (Polydiagnost, Germany), a rigid sheath-like accessory.11 Furthermore, although the PolyScope instrument as a whole is fragile, the reusable fibre-optic bundle seems durable, without any major alterations in function after 100 cycles of sterilization using either Steris System 1®(Steris Corporation, USA) or STERRAD®NX®(Johnson & Johnson, USA) systems.13 When sterilizing the reusable parts of this ‘disposable’ ureteroscope, as for other reusable endoscopes, following the manufacturers’ instructions regarding the substances and protocols that should be used is of utmost importance to preserve the qualities of outer coating or of the optical system. Another disposable flexible ureteroscope is the SemiFlex™ flexible ureteroscope (MaxiFlex, USA), which uses a G14732 Y‑port adaptor for irrigation (Cook Medical, USA). This instrument comes in two vari eties, one with a 55 cm shaft length and the other with a 65 cm shaft length; both variants have one 3.4F working channel, an 7.85F outer diameter and are completely disposable (Table 2). Thus, these instruments have additional advantages over other devices owing to elimination of the risk of patient to patient contamination and as supplementary costs relating to sterilization or repairs are negated. The published data suggest the technical features of the SemiFlex™ disposable ureteroscope are acceptable in comparison with commercially available reusable flexible ureteroscopes.14 The fact that different manufacturers have chosen vari ous divergent pathways for the development of flexible ureteroscopes confirms that the need for technological
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REVIEWS improvement is recognized and that efforts are being made to address this requirement. This observation also demonstrates that the maximum surgical potential of ureteroscopes is far from being reached.
Improved accessory instruments Energy sources The holmium laser At present, the holmium laser is probably the most- versatile energy source in the urologist’s armamentarium; this technology can be used with both semirigid and flexible ureteroscopes, can be applied to the fragmentation of stones, tissue incision or tumour ablation, and can even be used to cut lodged and immovable ancillary instruments to enable their disengagement.15,16 A key quality of the holmium laser is that it enables effective fragmentation of all types of stones.17 The development of this energy source markedly improved the efficacy of intracorporeal lithotripsy in comparison with other available devices, decreased associated morbidity, and expanded the indications of the ureteroscopic retrograde approach.18,19 In fact, in the European Association of Urology (EAU) guidelines on urolithiasis,20 the holmium laser is recommend as the gold-standard energy source for lithotripsy during ureteroscopy or flexible nephro scopy. The evolution of flexible ureteroscopes during the past decades is closely intertwined with establishment of the holmium laser into urological practice. However, one must keep in mind that the effectiveness of the holmium laser as an energy source also carries potential risks of damage to the ancillary instruments used during ureteroscopic procedures. The laser energy can cut through the wires of the baskets, for example, which not only increases costs owing to the need to replace the damaged instruments, but can also create protrusions and hooks that increase the risk of tissue injury. 21 Thus, careful handling of the endoscope to correctly position the optical fibres that carry the laser light, as well as ancillary instruments, is required to avoid such unwanted effects. Ultrasonic lithotripers With regard to the energy source used during retrograde semirigid ureteroscopy for lithotripsy, a sometimes neglected tool is the ultrasonic lithotripter, which combines the capacity for stone fragmentation and suction.22 As such, this methodology can prevent stone migration and enable quick and efficient removal of small stone fragments. Ultrasonic lithotripters can also be used alone or in combination with laser or ballistic devices, further increasing the potential for stone fragmentation and clearance.22
Ancillary instruments The ancillary instruments used during ureteroscopic procedures can be as important as the endoscopes, as the properties of accessory instruments sometimes have a dramatic influence over the performance of the latter. The past decades witnessed continuous efforts to increase accessibility and decrease morbidity associated
with such procedures through miniaturization of ureteroscopes. However, reducing the tip or outer diameters of the instruments comes at the price of reducing the available volume of the working and irrigation channel(s) (Table 1; Table 2). Choosing the most appropriate ancillary instruments for the specific ureteroscope and procedure is particularly important, especially when using flexible ureteroscopes, as the deflection capacity or irrigation flow of the endoscope are dependent on the devices used.23 For instance, a study by Bach and coworkers24 demonstrated a loss of irrigation volume of 53% when a 273 μm laser fibre was inserted into the 3.6F working channels of various flexible ureteroscopes, and by between 62% and 99% when 1.5F to 3.0F tools (tipless nitinol baskets or biopsy forceps) were used. Nitinol stone-extraction devices Nitinol (nickel–titanium alloy) extraction devices represent an important addition to the endourological armamentarium. Nitinol instruments provide additional advantages over conventional steel-wire baskets, such as increased durability and flexibility at the same diameter, which consequently influence both the efficacy and safety of stone extraction. In addition, instruments made of nitinol preserve the maximal deflection capabilities of flexible ureteroscopes, thus minimally influencing endoscope manoeuvrability.25 Furthermore, nitinol instruments are much thinner than similar instruments manufactured from alternate materials, which translates into less obstruction of the irrigation flow through the working channel and improved visibility. Indeed, stone retrieval baskets miniaturized to 1.2F in diameter when sheathed are currently available, and minimally hamper visibility during ureteroscopy.26 At present, various types of baskets are commercially available, with notable differences in the number of wires and specific architecture. However, the degree to which these parameters influence the performance of such devices is debatable. The tipless design—with no protrusion beyond the upper extremity of the basket—is probably the most important design from the practical point of view, as it reduces the risk of mucosal injury during manipulation within the renal calices. Considering these qualities, the EAU guidelines on urolithiasis20 recom mend tipless baskets as the only baskets suitable for retrograde intrarenal surgical procedures. Instruments for tumour biopsy The past decade was witness to a continuous trend towards diversification and specialization of ancillary instruments. In particular, the importance of the retro grade approach to upper urinary tract tumours for diagnostic as well as therapeutic purposes has driven the development of dedicated accessories. Tumour grading and stage can be independent predictive factors of oncological evolution, therefore, collection of adequate biopsy tissue for pathological assessment is important. Although tumour grade can be easily assessed, evaluation of the depth of invasion requires the isolation of good-quality tissue samples, as the accuracy of histopatological
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Figure 4 | Photograph of the Ntrap®antiretropulsion stone entrapment and extraction device (Cook Medical, USA). Before deployment, this device is held in a 2.8F sheath and, once deployed beyond the stone on which lithotripsy is to be performed, takes on an umbrella shape with a maximum diameter of 7 mm. The instrument prevents ascendant migration of the stone and stone fragments during lithotripsy, and enables urethral extraction of the fragments.
analyses is frequently dependent on the volume and/or depth of the biopsy specimen.27 However, although deep biopsy samples are more likely to comprise all layers of the upper urinary tract urothelium, such procedures are potentially associated with a greater risk of morbidity than more-superficial biopsies. Thus, a balance between the need to obtain pathological data with increased precision and patient safety is required. As such, various strate gies and ancillary instruments are used in the ureteroscopic sampling of tissues, and different methods can be used to complement each other. The simplest biopsy method is washing cytology, which enables samp ling of cells from the proximity of the tumour and can enable tumour grading, but never staging. Basic baskets or extractors can also be used to harvest tissue samples, and the smaller fragments can be histopathologically processed similarly to cytology samples. In addition, new instruments, such as BIGopsy®(Cook Medical, USA), have been developed to enable the isolation of large tissue samples, taking into account the limitations imposed by the size of ureteroscope working channels, which cannot be increased. The BIGopsy®device comprises backloading biopsy forceps with a collection cup that is large enough to provide samples that can be more accurately evaluated, and is especially useful for sampling flat or sessile lesions.28 The technical characteristics of this instrument impose restrictions on mode of deployment, necessitating the use of an access ureteral sheath (as recommended by the manufacturer). 29 However, that taking large tissue samples using such instruments might also correlate with an increased risk of mucosal injuries, bleeding or even ureteral perforations must be considered.
Managing the risk of stone-fragment migration Ascendant migration of stone fragments due to irrigation flow or retropulsive forces propagated by lithotripsy devices is a common cause of procedural failure during ureteroscopy. Consequently, various techniques and instruments have been developed to reduce or prevent the risk of this complication or to facilitate retrieval of the migrated stone fragments from the pyelocalyceal system. 378 | JULY 2014 | VOLUME 11
In comparison with pneumatic devices, the risk of stone-fragment retropulsion is substantially reduced when lasers in general—and holmium lasers in particular —are used as the energy source for lithotripsy.30 Moreover, this unwanted effect might be further prevented by choosing particular accessory equipment (such as laser fibres) or device settings. In this regard, analyses by Kang et al.31 demonstrated that shorter laser-pulse durations (tau‑p [τ‑p] = 120–190 microseconds [μs] at full width at maximum height [FWMH]) resulted in a greater distance of stone retropulsion than longer pulses (τ‑p = 210–350 μs at FWMH) at any given energy. Higher pulse energies, regardless of pulse duration, and larger optical fibres caused ablation of larger stone volumes but more retropulsion. These observations indicate that breaking stones into dust rather than small fragments by performing intracorporeal lithotripsy using thin laser fibres (273 μm, for example) with the laser set to low power (500W) and high frequency (12 Hz) might considerably reduce the risk of retropulsion.31,32 Although retropulsion risk is decreased by using these techniques and technologies, the risk is not entirely avoided. Thus, the selection and mode of use of the lithotripsy energy source alone does not solve the problem of stone-fragment retropulsion. The coupling of energy sources for lithotripsy with suction devices, such as LithoVac® (Boston Scientific, USA), was one solution developed to further minimize unwanted ascendant stone migration.33 Antiretropulsion ancillary instruments represent an additional area of technical development in this context. This approach relies on the deployment of occlusion devices beyond the ureteral segment in which lithotripsy is performed to physically obstruct any ascendant migration of the resultant stone fragments. One of the first examples of such devices, which has proven efficiency and safety after years of clinical use, 34 was the Stone Cone™ (Boston Scientific, USA). This nitinol stone-retrieval device is a 3F wire comprising a region that can be coiled into a cone with a maximum diameter of 7 mm or 10 mm once in position beyond the stone, which is used prevent retropulsion. 34 Since this instrument was introduction to the clinical arena, many other occlusion devices have been developed, and two well-established devices are the Accordion®(PercSys, USA)35 and NTrap® (Cook Medical, USA; Figure 4).36 With a functional principle similar to the Stone Cone™, these instruments not only enable stone entrapment but also have utility in extraction of the calculi fragments at the end of the lithotripsy process.35,36 Data comparing the effectiveness of such devices are controversial, with some authors advocating particular tools,37 whereas others researchers have described similar results for all occlusion devices. 38 However, evidence unanimously indicates that all the currently available tools in this class of ancillary instrument meet their primary goal of redu cing stone migration and implicitly improve uretero scopy outcomes. In addition, other devices developed for different purposes, such as the Passport™ Balloon (Boston Scientific, USA), an access and dilation instrument, have been reported prevent stone migration.33
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REVIEWS Instillation of lidocaine jelly beyond the stone has also been used as an alternative method of preventing stone migration during lithotripsy;39 however the effectiveness of this approach seems modest compared with occlusion devices such as the Stone Cone™ and the Accordion®.40,41 Nevertheless, more promising outcomes have been demonstrated using a newly developed water-soluble polymeric gel, BackStop® (Boston Scientific, USA).42 In particular, the behaviour of BackStop® gel in the ureter and related effectiveness of the approach seem to be substantially more predictable than those observed for lidocaine jelly.42 A key explanation for this finding is that Backstop® demonstrates a property called reverse thermosensitivity: at body temperature, the viscosity of the gel increases so that it forms a plug after deployment beyond the stone; however, when irrigated with colder saline solution, the gel becomes fluid again and can be flushed from the ureter.42 Although these devices, materials, and techniques all increase the immediate cost of ureteroscopy, they can prevent additional expenses resulting from prolonged operating-room time or the requirement for additional procedures to remove ascended stone fragments. In this regard, purchasing antiretropulsion tools has been calcu lated to be cost-effective if ascendant migration of the stone is recorded in at least 6.3% of the patients who are treated using a retrograde ureteroscopic approach.43 Ultimately, one of the most-effective instruments in the case of stone-fragment retropulsion is the flexible ureteroscope, which provides access to the entire pyelocalyceal system, including the lower calyx, enabling migrated stone fragments to be located and treated. Owing to the existence of flexible ureteroscopes, retro pulsion no longer represents a cause of procedural failure. Indeed, these endoscopes are one of the reasons why the use of retrograde intracorporeal lithotripsy is now starting to surpass extracorporeal shockwave litho tripsy (ESWL) in the treatment of proximal ureteral stones, especially for stones >1 cm in diameter.44–46
Expanding indications for ureteroscopy Addition of the flexible ureteroscopes to the endourological armamentarium tends to result in a shift in the treatment modality used for upper ureteral or pyelo calyceal stones from ESWL to a retrograde ureteroscopic approach. However, the best technique for the management of stones in the lower pole, in particular, remains a debatable issue. The EAU guidelines20 state that retrograde intrarenal surgery using flexible ureteroscopes can be appropriate for the treatment of pyelo calyceal stones in patients with unfavourable predictors of ESWL outcome, which includes patients with an acute infundibular angle, long lower-pole calyx (>10 mm) or a narrow infundibulum (1.5 cm in diameter, percutaneous surgery or retrograde ureteroscopic lithotripsy are recommended because of the limited efficacy of ESWL in this context.20 However, the general shift towards recommendation of ESWL for the treatment of pyelocalyceal stones, rather
than ureteroscopy, in the current issue of the EAU guidelines20 is a consequence of the apparent similarity between the efficacy of this approach and retrograde uretero scopic lithotripsy, but the reduced invasiveness of the extracorporeal approach.47,48 However, one should bear in mind that these recommendations are based on data gathered over at least one decade and, therefore, include the outcomes of a substantial number of ureteroscopy procedures performed using older and less-effective models of flexible ureteroscopes than are currently available. Indeed, in their publication,20 the EAU guidelines panel stated that stone-free rates will probably continue to improve with the evolution of ureteroscopy. In studies evaluating data solely related to the use of the latest generation of endoscopes, the ureterorenoscopic approach seems to be more efficacious than extracorporeal lithotripsy.49,50 Flexible ureteroscopy creates the possibility of approaching multiple stones, regardless of their location51 and sometimes during a single procedure. Furthermore, reports of promising results of retrograde intrarenal lithotripsy in patients with large stones (>2 cm) have emerged, although removal of this stone burden often required staged ureteroscopic intervention.50,52–56 Together, these data suggest that future updates of the current EAU guidelines are not only possible but probable. For distal ureteral stones, the results of ureteroscopic lithotripsy have been shown to be clearly superior to those possible with ESWL, whereas no such difference in the overall stone-free rate was observed for the treatment of stones located in the proximal ureter.20 Indeed, analysis of the stone-free rates after the treatment of proximal ureteral stones using ESWL or ureteroscopy revealed a similar situation to that observed for pyelo calyceal stones.20 When stone size was considered, ESWL resulted in a higher stone-free rate than the retrograde ureteroscopic approach in proximal urethral stones
Introduction
Urological Department, Saint John Emergency Clinical Hospital, Vitan Barzesti 13, Bucharest 042122, Romania (P.G., R.M., B.G.). Correspondence to: P.G. [email protected]
The past decades have witnessed dramatic changes in ureteroscopy, which has led to this methodology becoming a routine procedure in many urological clinics worldwide, especially for the treatment of urolithiasis and in the diagnosis of upper urinary tract pathology. The adoption of ureteroscopic procedures into the daily management of these conditions has resulted in enormous quantities of clinical data. Together with technological progression, this wealth of clinical experience has driven the development of novel solutions to expand the indications and increase the efficacy of the upper urinary tract endoscopic retrograde approach, and decrease associated morbidity and costs. Of note, ureteroscopic urolithotripsy is now feasible in pregnant women or in patients with urinary diversions, and pyelocalyceal diverticulum, infundibular stenosis, and upper urinary tract tumours can also be managed using this methodology. In particular, miniaturization, the addition of digital optical systems and second working channels to ureteroscopes, and the introduction of disposable apparatus represent key advances in the utility of this methodology. In parallel, the introduction of holmium lasers has enabled effective and accurate tissue incision, tumour ablation, and intracorporeal lithotripsy, Competing interests B.G. declares that he is a member of the speakers’ bureau and has received honouraria from Olympus. The other authors declare no competing interests.
and modern ancillary tools can be used, for example, to minimize ascendant migration of stone fragments. Importantly, the evolution of ureteroscopy is ongoing, with multiple manufacturers finding different technical solutions to further increase the performance and versatility of endoscopes and ancillary instruments. Such developments, as well as advances in robot-assisted procedures, hold great promise in improving the efficacy and safety of ureteroscopy and, therefore, the management of urological conditions. In a review published in 2008, Holden et al.1 stated that “endourology could be redefined as ‘enginurology’, as the marriage between engineering and urology”; this postulate is probably more appropriate for ureteroscopy than any other procedure. Herein, we review the current status of ureteroscopy, focusing on the technical advances that have been made to date. In addition, we highlight how these developments and continued efforts to adapt and improve ureteroscopy apparatus and protocols could increase the effectiveness and broaden the utility of the endoscopic retrograde approach in the future.
New-generation ureteroscopes Current rigid and semirigid ureteroscopes Initially developed as an extension of cystoscopy, uretero scopy has become a key technique in the diagnosis and treatment of a number of urological conditions. The first ureteroscopes, introduced in the late 1970s, were rigid or
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REVIEWS Key points ■■ Ureteroscopy is a routine procedure used in the treatment of conditions such as urolithiasis and in the diagnosis of upper urinary tract pathology in many centres worldwide ■■ Ureteroscopy with flexible endoscopes, in particular, is important in the resolution of various pathological events, such as pyelocalyceal lithiasis, migrated stone fragments, pyelocalyceal diverticulum, and renal infundibular stenosis ■■ New semirigid and flexible endoscopes designed for ureteroscopy, with either fibre-optic or digital optical imaging systems, are continuously being improved and developed ■■ The holmium laser is the most-efficient and most-versatile energy source used in ureteroscopy procedures, enabling tissue incision, tumour ablation or intracorporeal lithotripsy ■■ In addition, novel accessory devices are being incorporated into routine clinical ureteroscopy procedures to minimize retropulsion and ascendant migration of stone fragments
semirigid, and were shorter, thicker and more cumbersome than the current instruments; therefore, the use of these instruments was limited to the management of a small numbers of lesions of the distal ureter. In the subsequent decades, rigid and semirigid ureteroscopes were continuously refined, becoming longer and thinner, and enabled access to the proximal ureter and parts of the pyelocalyceal system. However, the maximum potential for development of rigid and semirigid ureteroscopes aimed at improving the management of urological conditions was seemingly reached some time ago. In fact, the develop ment of semirigid ureteroscopes with digital imaging systems (rather than fibre-optic imaging systems), such as the EndoEye video ureteroscope (Olympus Europe, Germany), might be considered the only major technological achievement made with regard to rigid or semirigid ureteroscopy during the past two decades.2 Nevertheless, miniaturization has also been a key focus in the development of semirigid ureteroscopes; The Needle ureteroscope
(Richard Wolf, Germany) has a tip diameter of only 4.5F and a shaft diameter of 6.5F, and is suitable for use in paediatric or adolescent patients. Technical parameters of these and some of the other commercially available models of semirigid ureteroscopes are summarized in Table 1.
The development of flexible ureteroscopes Improved imaging In comparison with the apparent plateau in the development of rigid and semirigid ureteroscopy platforms, the advancement of flexible ureteroscopy instrumentation is still in a period of continuous evolution. First developed during the 1980s by Bagley and colleagues,3 flexible ureteroscopes have the major advantage of being able to reach, at least theoretically, the entire upper urinary tract using the anatomical passages of the urinary system. However, the performance and utility of such apparatus were limited for a prolonged period of time by poor visi bility and sometimes impaired manoeuvrability in use, as well as their fragility and high cost in comparison with the semirigid ureteroscopes that were available during the same period. Over the past decade, the development of flexible ureteroscopes with digital optical systems has largely solved the visibility issue, with modern models such as the Flex-Xc (KARL STORZ Endoskope, Germany) or the URF‑V (Olympus Europe, Germany) generally providing an endoscopic field of view that is larger and clearer compared with fibre-optic models (Figure 1), and sometimes even semirigid apparatus from the same manufacturers. Differences between these two models of flexible video ureteroscopes exist: the Flex-Xc is thinner at the tip and highly manoeuvrable, with a greater upwards deflection angle (270° versus 180°; Table 2), whereas the URF‑V has a larger diameter (Figure 2), which creates some potential access problems in the narrow segments of the upper urinary tract; however, the latter model offers a larger
Table 1 | Technical characteristics of selected semirigid ureteroscopes Manufacturer and model
Number and diameter of channels
Tip diameter
Outer diameter
Length of shaft
Optical system
OES Pro
Single: 4.2F
6.4F
7.8F
33 cm or 43 cm
Fibre-optic
OES Pro
Single: 6.4F
8.6F
9.8F
43 cm
Fibre-optic
OES 4,000
Dual: 2.4F and 3.4F
NA
7.5F
43 cm
Fibre-optic
EndoEye video ureteroscope
Single: 4.2F
8.5F
9.9F
43 cm
Digital (CCD)
The Needle
Single: 3F
4.5F
6.5F
31.5 cm or 43 cm
Fibre-optic
The Ultrathin
Single: 4F
6F
7.5F
33 cm or 43 cm
Fibre-optic
The D.O.C.
Dual: 4F and 2.4F
6.5F
8.5F
33 cm or 43 cm
Fibre-optic
Olympus (Germany)
Richard Wolf (Germany)
KARL STORZ Endoskope (Germany) MICHEL Uretero-Renoscope
Dual: 3F and 2.3F*
9F
9.5F or 12F
43 cm
Fibre-optic
Uretero-Renoscope
Single: 4.8F
6.5F
7F or 9.9F
34 cm or 43 cm
Fibre-optic
Uretero-Renoscope
Single: 5F
7F
8F or 12F
34 cm or 43 cm
Fibre-optic
Uretero-Renoscope
Single: 6F
8F
9.5F or 12F
34 cm or 43 cm
Fibre-optic
Uretero-Renoscope
Dual: 3.4F and 2.4F*
7F
7F or 8.4–9.9F
34 cm or 43 cm
Fibre-optic
*The smaller channel in these apparatus can only be used for irrigation purposes. Abbreviations: CCD, charged-coupled device; NA, data not available.
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REVIEWS a
(the tumour-detection rate was unchanged in the other patients assessed).5 However, authors of this study conclude that, in their opinion, the NBI-based procedure for detection of urothelial tumours they describe cannot be recommended for use in daily practice at present.5 Further validation of the technique is, therefore, required.
b
Figure 1 | Comparison of the current imaging capabilities of flexible ureteroscopes. The two images shown demonstrate the differences in image resolution between a | the fibre-optic Richard Wolf Cobra flexible ureteroscope and b | a Olympus URF‑V device with a digital optical system. At present, the image quality obtained with fibreoptic ureteroscopes cannot match the quality of those with digital imaging capability.
endoscopic field of view and is the only flexible ureteroscope with narrow-band imaging (NBI) capabilities.4 NBI is an optical image-enhancement technology that, unlike white-light imaging, relies on emission of two specific wavelengths of light with high absorbance by haemo globin: blue light of 415 nm, which penetrates the superficial layers of the mucosa and causes vessels within this tissue to appear brown; and 540 nm green light, which has greater tissue penetration and makes deeper vessels appear cyan. Thus, NBI increases the visibility of blood vessels and other structures within the urothelium, and the main purpose of this technology is to improve tumour detection. In this context, the first clinical experience of NBI demonstrated the promise of this approach, as the upper urinary tract urothelial tumour-detection rate was improved by 22.7% among in seven (25.9%) of 27 patients studied, compared with conventional white-light ureteroscopy
Miniaturization Although the digital flexible ureteroscopes now provide a good level of visibility, attempts to further miniaturize apparatus are ongoing. One of the latest models of conventional flexible ureteroscope, the URF‑P6/P6R (Olympus Europe, Germany), has the advantage of a super-slim design with a maximal outer-shaft diameter of 7.95F and a tip diameter of only 4.9F (Table 2). The small diameter of this instrument, together with the incorporation of a stiffer shaft than other flexible scopes currently available, can simplify insertion of the ureteroscope and improve access ibility to the upper urinary tract. As the URF‑P6/P6R uses a fibre-optic imaging system, this instrument cannot match the performance of current digital video ureteroscopes with regard to visibility;4,6 however, the URF‑P6/ P6R uses a moiré filter to enhance imaging accuracy in an attempt to at least partially solve this problem. Incorporation of dual working channels The manufacturer of the Cobra flexible ureteroscope (Richard Wolf, Germany) chose a different approach to improving visibility during ureteroscopy procedures: the addition of a second working channel (Figure 3; Table 2). This modification enables unimpaired irrigation flow and the simultaneous use of ancillary instruments, therefore, providing a clearer field of view than is possible with single-channel ureteroscopes that often suffer from severe loss or even interruption of irrigation when ancillary instruments are in use.7 More importantly, the inclusion of
Table 2 | Technical characteristics of selected flexible ureteroscopes Manufacturer and model
Number and diameter of channels
Tip diameter
Outer diameter
Length of shaft
Optical system
Maximum deflection (down/up)
URF‑V
Single: 3.6F
8.5F
9.9F
67 cm
Digital
275o/180o
URF‑P5
Single: 3.6F
5.3F
8.4F
70 cm
Fibre-optic
275o/180o
URF‑P6
Single: 3.6F
4.9F
7.95F
67 cm
Fibre-optic
275o/275o
Viper
Single: 3.6F
6F
8.8F
68 cm
Fibre-optic
270o/270o
Cobra
Dual: both 3.3F
6F
9.9F
68 cm
Fibre-optic
270o/270o
Olympus (Germany)
Richard Wolf (Germany)
KARL STORZ Endoskope (Germany) Flex‑X2
Single: 3.6F
7.5F
8.4F
67 cm
Fibre-optic
270o/270o
Flex-Xc
Single: 3.6F
7.8F
8.5F
70 cm
Digital
270o/270o
Single: 3.5F
8F
8F
85 cm
Fibre-optic
180o*
SemiFlex™ Endo55
Single: 3.4F
6.4F
7.85F
55 cm
Fibre-optic
210o/210o
SemiFlex™ Endo65
Single: 3.4F
6.4F
7.85F
65 cm
Fibre-optic
210o/210o
Lumenis (Israel) PolyScope MaxiFlex (USA)
*180 single direction deflection but the instrument can be rotated 360 . o
o
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b
Figure 2 | Olympus URF‑V (top) and KARL STORZ Endoskope Flex-Xc (bottom) ureteroscopes. a | Photograph of the ureteroscopes bodies demonstrating the control modules. b | Photograph showing the distal working parts of these flexible ureteroscopes at maximum downwards deflection (275o and 270o, respectively). Both of these devices are fitted with digital optical systems. The instruments also both have a single channel of the same diameter (3.6F), although the URF‑V instrument is clearly slightly larger than the Flex‑Xc model, with outer diameter of 9.9F versus 8.5F (tip diameters of 8.5F and 7.8F respectively).
a
b
Figure 3 | The Richard Wolf Cobra, the first dual channel flexible ureteroscope. a | Photograph showing the proximal parts of the device, in which the entry points to the two channels within the endoscope are visible, as is the eyepiece for the fibre-optic imaging device. The inclusion of two 3.3F channels enables laser fibres up to a maximum of 365 μm to be accommodated in a separate working channel that incorporates a ‘laser shifter’ for better control, which together might improve the precision, and reduce the damage to tissues and the instrument itself caused by the laser. b | This image shows details of the tip of the device at maximum deflection; this instrument has the same upwards and downwards deflection of 270o, and has outer and tip diameters of 9.9F and 6F, respectively.
dual working channels enables simultaneous insertion of ancillary instruments in different combinations, thus creating new procedural opportunities.7 Improved durability Improvements have reduced the previous fragility dis advantage of flexible ureteroscopes compared with semirigid and rigid models; the durability of the new flexible endoscopes seems to be superior to the older flexible ureteroscopes, ultimately translating into reduced interventional costs.8 A paper reported the use of the Flex-Xc model for a mean number of 135 procedures per ureteroscope, and one uretersocope was used for 159 procedures before major repairs were needed.9 By comparison, published experience with older flexible ureteroscopes, such as the DUR 8 or DUR 8‑Elite models (ACMI Corporation, USA; now part of Olympus), 11274AA (KARL STORZ Endoskope, Germany), 7325.172‑7.5F or 7330.072‑9.0F (Richard Wolf, Germany) and URF‑P3 (Olympus Europe, Germany), indicated that only 10 to 34 procedures were possible before breakages occurred.10 376 | JULY 2014 | VOLUME 11
Disposable flexible ureteroscopes The PolyScope (Lumenis, Israel), a disposable flexible ureteroscope composed of a single-use flexible catheter and a reusable fibre-optic bundle, was developed with the main aim of decreasing costs associated with ureteros copy (Table 2). The multilumen disposable catheters used with this device are relatively cheap in comparison with reusable ureteroscopes, preclude the requirement for sterilization of the ureteroscope shaft, thus minimizing the risk of instrument-related infection, and simplify sterilization of the optical cable, reducing the chances of procedural and postprocedural damage to the imaging system that is a frequent occurrence with other models of multiuse flexible ureteroscopes.11 Initial data on the clinical use of the PolyScope indicate that the instrument is safe, convenient, and effective for the lithotripsy of upper urinary tract calculi and, therefore, confirm the theoretical promise attributed to disposable ureteroscopes.11 With regard to technical performance, the optical system used in the PolyScope provides 10,000 pixels resolution, enabling the visualization of targets 0.125 mm in size within a range of 2–4 mm without moiré effect, and has a 3.6F working channel, similar to that of most reusable flexible ureteroscopes.12 Although cheaper to buy and less costly to use repeatedly, this disposable apparatus does not solve the manoeuvrability issues associated with other flexible ureteroscopes and is similarly fragile.12 However, the PolyScope can also be used as a rigid or semirigid ureteroscope if necessary, by inserting it through ChiRiFlex (Polydiagnost, Germany), a rigid sheath-like accessory.11 Furthermore, although the PolyScope instrument as a whole is fragile, the reusable fibre-optic bundle seems durable, without any major alterations in function after 100 cycles of sterilization using either Steris System 1®(Steris Corporation, USA) or STERRAD®NX®(Johnson & Johnson, USA) systems.13 When sterilizing the reusable parts of this ‘disposable’ ureteroscope, as for other reusable endoscopes, following the manufacturers’ instructions regarding the substances and protocols that should be used is of utmost importance to preserve the qualities of outer coating or of the optical system. Another disposable flexible ureteroscope is the SemiFlex™ flexible ureteroscope (MaxiFlex, USA), which uses a G14732 Y‑port adaptor for irrigation (Cook Medical, USA). This instrument comes in two vari eties, one with a 55 cm shaft length and the other with a 65 cm shaft length; both variants have one 3.4F working channel, an 7.85F outer diameter and are completely disposable (Table 2). Thus, these instruments have additional advantages over other devices owing to elimination of the risk of patient to patient contamination and as supplementary costs relating to sterilization or repairs are negated. The published data suggest the technical features of the SemiFlex™ disposable ureteroscope are acceptable in comparison with commercially available reusable flexible ureteroscopes.14 The fact that different manufacturers have chosen vari ous divergent pathways for the development of flexible ureteroscopes confirms that the need for technological
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REVIEWS improvement is recognized and that efforts are being made to address this requirement. This observation also demonstrates that the maximum surgical potential of ureteroscopes is far from being reached.
Improved accessory instruments Energy sources The holmium laser At present, the holmium laser is probably the most- versatile energy source in the urologist’s armamentarium; this technology can be used with both semirigid and flexible ureteroscopes, can be applied to the fragmentation of stones, tissue incision or tumour ablation, and can even be used to cut lodged and immovable ancillary instruments to enable their disengagement.15,16 A key quality of the holmium laser is that it enables effective fragmentation of all types of stones.17 The development of this energy source markedly improved the efficacy of intracorporeal lithotripsy in comparison with other available devices, decreased associated morbidity, and expanded the indications of the ureteroscopic retrograde approach.18,19 In fact, in the European Association of Urology (EAU) guidelines on urolithiasis,20 the holmium laser is recommend as the gold-standard energy source for lithotripsy during ureteroscopy or flexible nephro scopy. The evolution of flexible ureteroscopes during the past decades is closely intertwined with establishment of the holmium laser into urological practice. However, one must keep in mind that the effectiveness of the holmium laser as an energy source also carries potential risks of damage to the ancillary instruments used during ureteroscopic procedures. The laser energy can cut through the wires of the baskets, for example, which not only increases costs owing to the need to replace the damaged instruments, but can also create protrusions and hooks that increase the risk of tissue injury. 21 Thus, careful handling of the endoscope to correctly position the optical fibres that carry the laser light, as well as ancillary instruments, is required to avoid such unwanted effects. Ultrasonic lithotripers With regard to the energy source used during retrograde semirigid ureteroscopy for lithotripsy, a sometimes neglected tool is the ultrasonic lithotripter, which combines the capacity for stone fragmentation and suction.22 As such, this methodology can prevent stone migration and enable quick and efficient removal of small stone fragments. Ultrasonic lithotripters can also be used alone or in combination with laser or ballistic devices, further increasing the potential for stone fragmentation and clearance.22
Ancillary instruments The ancillary instruments used during ureteroscopic procedures can be as important as the endoscopes, as the properties of accessory instruments sometimes have a dramatic influence over the performance of the latter. The past decades witnessed continuous efforts to increase accessibility and decrease morbidity associated
with such procedures through miniaturization of ureteroscopes. However, reducing the tip or outer diameters of the instruments comes at the price of reducing the available volume of the working and irrigation channel(s) (Table 1; Table 2). Choosing the most appropriate ancillary instruments for the specific ureteroscope and procedure is particularly important, especially when using flexible ureteroscopes, as the deflection capacity or irrigation flow of the endoscope are dependent on the devices used.23 For instance, a study by Bach and coworkers24 demonstrated a loss of irrigation volume of 53% when a 273 μm laser fibre was inserted into the 3.6F working channels of various flexible ureteroscopes, and by between 62% and 99% when 1.5F to 3.0F tools (tipless nitinol baskets or biopsy forceps) were used. Nitinol stone-extraction devices Nitinol (nickel–titanium alloy) extraction devices represent an important addition to the endourological armamentarium. Nitinol instruments provide additional advantages over conventional steel-wire baskets, such as increased durability and flexibility at the same diameter, which consequently influence both the efficacy and safety of stone extraction. In addition, instruments made of nitinol preserve the maximal deflection capabilities of flexible ureteroscopes, thus minimally influencing endoscope manoeuvrability.25 Furthermore, nitinol instruments are much thinner than similar instruments manufactured from alternate materials, which translates into less obstruction of the irrigation flow through the working channel and improved visibility. Indeed, stone retrieval baskets miniaturized to 1.2F in diameter when sheathed are currently available, and minimally hamper visibility during ureteroscopy.26 At present, various types of baskets are commercially available, with notable differences in the number of wires and specific architecture. However, the degree to which these parameters influence the performance of such devices is debatable. The tipless design—with no protrusion beyond the upper extremity of the basket—is probably the most important design from the practical point of view, as it reduces the risk of mucosal injury during manipulation within the renal calices. Considering these qualities, the EAU guidelines on urolithiasis20 recom mend tipless baskets as the only baskets suitable for retrograde intrarenal surgical procedures. Instruments for tumour biopsy The past decade was witness to a continuous trend towards diversification and specialization of ancillary instruments. In particular, the importance of the retro grade approach to upper urinary tract tumours for diagnostic as well as therapeutic purposes has driven the development of dedicated accessories. Tumour grading and stage can be independent predictive factors of oncological evolution, therefore, collection of adequate biopsy tissue for pathological assessment is important. Although tumour grade can be easily assessed, evaluation of the depth of invasion requires the isolation of good-quality tissue samples, as the accuracy of histopatological
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Figure 4 | Photograph of the Ntrap®antiretropulsion stone entrapment and extraction device (Cook Medical, USA). Before deployment, this device is held in a 2.8F sheath and, once deployed beyond the stone on which lithotripsy is to be performed, takes on an umbrella shape with a maximum diameter of 7 mm. The instrument prevents ascendant migration of the stone and stone fragments during lithotripsy, and enables urethral extraction of the fragments.
analyses is frequently dependent on the volume and/or depth of the biopsy specimen.27 However, although deep biopsy samples are more likely to comprise all layers of the upper urinary tract urothelium, such procedures are potentially associated with a greater risk of morbidity than more-superficial biopsies. Thus, a balance between the need to obtain pathological data with increased precision and patient safety is required. As such, various strate gies and ancillary instruments are used in the ureteroscopic sampling of tissues, and different methods can be used to complement each other. The simplest biopsy method is washing cytology, which enables samp ling of cells from the proximity of the tumour and can enable tumour grading, but never staging. Basic baskets or extractors can also be used to harvest tissue samples, and the smaller fragments can be histopathologically processed similarly to cytology samples. In addition, new instruments, such as BIGopsy®(Cook Medical, USA), have been developed to enable the isolation of large tissue samples, taking into account the limitations imposed by the size of ureteroscope working channels, which cannot be increased. The BIGopsy®device comprises backloading biopsy forceps with a collection cup that is large enough to provide samples that can be more accurately evaluated, and is especially useful for sampling flat or sessile lesions.28 The technical characteristics of this instrument impose restrictions on mode of deployment, necessitating the use of an access ureteral sheath (as recommended by the manufacturer). 29 However, that taking large tissue samples using such instruments might also correlate with an increased risk of mucosal injuries, bleeding or even ureteral perforations must be considered.
Managing the risk of stone-fragment migration Ascendant migration of stone fragments due to irrigation flow or retropulsive forces propagated by lithotripsy devices is a common cause of procedural failure during ureteroscopy. Consequently, various techniques and instruments have been developed to reduce or prevent the risk of this complication or to facilitate retrieval of the migrated stone fragments from the pyelocalyceal system. 378 | JULY 2014 | VOLUME 11
In comparison with pneumatic devices, the risk of stone-fragment retropulsion is substantially reduced when lasers in general—and holmium lasers in particular —are used as the energy source for lithotripsy.30 Moreover, this unwanted effect might be further prevented by choosing particular accessory equipment (such as laser fibres) or device settings. In this regard, analyses by Kang et al.31 demonstrated that shorter laser-pulse durations (tau‑p [τ‑p] = 120–190 microseconds [μs] at full width at maximum height [FWMH]) resulted in a greater distance of stone retropulsion than longer pulses (τ‑p = 210–350 μs at FWMH) at any given energy. Higher pulse energies, regardless of pulse duration, and larger optical fibres caused ablation of larger stone volumes but more retropulsion. These observations indicate that breaking stones into dust rather than small fragments by performing intracorporeal lithotripsy using thin laser fibres (273 μm, for example) with the laser set to low power (500W) and high frequency (12 Hz) might considerably reduce the risk of retropulsion.31,32 Although retropulsion risk is decreased by using these techniques and technologies, the risk is not entirely avoided. Thus, the selection and mode of use of the lithotripsy energy source alone does not solve the problem of stone-fragment retropulsion. The coupling of energy sources for lithotripsy with suction devices, such as LithoVac® (Boston Scientific, USA), was one solution developed to further minimize unwanted ascendant stone migration.33 Antiretropulsion ancillary instruments represent an additional area of technical development in this context. This approach relies on the deployment of occlusion devices beyond the ureteral segment in which lithotripsy is performed to physically obstruct any ascendant migration of the resultant stone fragments. One of the first examples of such devices, which has proven efficiency and safety after years of clinical use, 34 was the Stone Cone™ (Boston Scientific, USA). This nitinol stone-retrieval device is a 3F wire comprising a region that can be coiled into a cone with a maximum diameter of 7 mm or 10 mm once in position beyond the stone, which is used prevent retropulsion. 34 Since this instrument was introduction to the clinical arena, many other occlusion devices have been developed, and two well-established devices are the Accordion®(PercSys, USA)35 and NTrap® (Cook Medical, USA; Figure 4).36 With a functional principle similar to the Stone Cone™, these instruments not only enable stone entrapment but also have utility in extraction of the calculi fragments at the end of the lithotripsy process.35,36 Data comparing the effectiveness of such devices are controversial, with some authors advocating particular tools,37 whereas others researchers have described similar results for all occlusion devices. 38 However, evidence unanimously indicates that all the currently available tools in this class of ancillary instrument meet their primary goal of redu cing stone migration and implicitly improve uretero scopy outcomes. In addition, other devices developed for different purposes, such as the Passport™ Balloon (Boston Scientific, USA), an access and dilation instrument, have been reported prevent stone migration.33
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REVIEWS Instillation of lidocaine jelly beyond the stone has also been used as an alternative method of preventing stone migration during lithotripsy;39 however the effectiveness of this approach seems modest compared with occlusion devices such as the Stone Cone™ and the Accordion®.40,41 Nevertheless, more promising outcomes have been demonstrated using a newly developed water-soluble polymeric gel, BackStop® (Boston Scientific, USA).42 In particular, the behaviour of BackStop® gel in the ureter and related effectiveness of the approach seem to be substantially more predictable than those observed for lidocaine jelly.42 A key explanation for this finding is that Backstop® demonstrates a property called reverse thermosensitivity: at body temperature, the viscosity of the gel increases so that it forms a plug after deployment beyond the stone; however, when irrigated with colder saline solution, the gel becomes fluid again and can be flushed from the ureter.42 Although these devices, materials, and techniques all increase the immediate cost of ureteroscopy, they can prevent additional expenses resulting from prolonged operating-room time or the requirement for additional procedures to remove ascended stone fragments. In this regard, purchasing antiretropulsion tools has been calcu lated to be cost-effective if ascendant migration of the stone is recorded in at least 6.3% of the patients who are treated using a retrograde ureteroscopic approach.43 Ultimately, one of the most-effective instruments in the case of stone-fragment retropulsion is the flexible ureteroscope, which provides access to the entire pyelocalyceal system, including the lower calyx, enabling migrated stone fragments to be located and treated. Owing to the existence of flexible ureteroscopes, retro pulsion no longer represents a cause of procedural failure. Indeed, these endoscopes are one of the reasons why the use of retrograde intracorporeal lithotripsy is now starting to surpass extracorporeal shockwave litho tripsy (ESWL) in the treatment of proximal ureteral stones, especially for stones >1 cm in diameter.44–46
Expanding indications for ureteroscopy Addition of the flexible ureteroscopes to the endourological armamentarium tends to result in a shift in the treatment modality used for upper ureteral or pyelo calyceal stones from ESWL to a retrograde ureteroscopic approach. However, the best technique for the management of stones in the lower pole, in particular, remains a debatable issue. The EAU guidelines20 state that retrograde intrarenal surgery using flexible ureteroscopes can be appropriate for the treatment of pyelo calyceal stones in patients with unfavourable predictors of ESWL outcome, which includes patients with an acute infundibular angle, long lower-pole calyx (>10 mm) or a narrow infundibulum (1.5 cm in diameter, percutaneous surgery or retrograde ureteroscopic lithotripsy are recommended because of the limited efficacy of ESWL in this context.20 However, the general shift towards recommendation of ESWL for the treatment of pyelocalyceal stones, rather
than ureteroscopy, in the current issue of the EAU guidelines20 is a consequence of the apparent similarity between the efficacy of this approach and retrograde uretero scopic lithotripsy, but the reduced invasiveness of the extracorporeal approach.47,48 However, one should bear in mind that these recommendations are based on data gathered over at least one decade and, therefore, include the outcomes of a substantial number of ureteroscopy procedures performed using older and less-effective models of flexible ureteroscopes than are currently available. Indeed, in their publication,20 the EAU guidelines panel stated that stone-free rates will probably continue to improve with the evolution of ureteroscopy. In studies evaluating data solely related to the use of the latest generation of endoscopes, the ureterorenoscopic approach seems to be more efficacious than extracorporeal lithotripsy.49,50 Flexible ureteroscopy creates the possibility of approaching multiple stones, regardless of their location51 and sometimes during a single procedure. Furthermore, reports of promising results of retrograde intrarenal lithotripsy in patients with large stones (>2 cm) have emerged, although removal of this stone burden often required staged ureteroscopic intervention.50,52–56 Together, these data suggest that future updates of the current EAU guidelines are not only possible but probable. For distal ureteral stones, the results of ureteroscopic lithotripsy have been shown to be clearly superior to those possible with ESWL, whereas no such difference in the overall stone-free rate was observed for the treatment of stones located in the proximal ureter.20 Indeed, analysis of the stone-free rates after the treatment of proximal ureteral stones using ESWL or ureteroscopy revealed a similar situation to that observed for pyelo calyceal stones.20 When stone size was considered, ESWL resulted in a higher stone-free rate than the retrograde ureteroscopic approach in proximal urethral stones
