Semirigid

Semirigid ureteroscopes remain an essential component for endourologists to treat stones. They are usually utilized to treat stones in the ureter below the pelvic brim, but also in the mid- and upper ureter in females and occasionally males. Technology for semirigid ureteroscopes has been relatively stable over the past decade. The majority of the semirigid ureteroscopes are fiber-optic and therefore do not have the half-moon effect that a rod-lens-based scope would have when they are flexed. Semirigid ureteroscopes are available in different lengths, ranging from approximately 310 up to 450 mm depending on the make and model. The shorter ureteroscopes are easier to handle and are usually adequate to reach stones in the distal and mid-ureter in men, and throughout the entire ureter in women. The longer semirigid ureteroscopes can be used to reach the upper ureter in men and renal pelvis in both sexes, provided they can be passed without resistance.

There has been a trend toward miniaturization with semirigid ureteroscopes. Most modern semirigid ureteroscopes have a tip diameter of 7 Fr or less and then usually increase in diameter slightly through the shaft. Designs exist with either one large working channel (≈ 4.5 Fr) or two smaller channels (≈ 2–3 Fr) (Fig. 11.8). The advantage of the single channel is that a larger instrument can be accommodated, but irrigation flow may be compromised since the channel is shared. With two separate working channels, one is typically used for the instrument, while the second channel is dedicated for irrigation.

One other differentiating factor for semirigid ureteroscopes is an offset versus a straight lens configuration. An offset lens allows for a straight working channel that will accommodate a rigid instrument such as a pneumatic lithotripsy probe. However, if holmium:YAG laser lithotripsy is the preferred lithotrite, then the working channel does not need to be straight, and an offset lens is not required since the laser fiber is flexible. In my own practice, I find a semirigid ureteroscope with a straight lens more ergonomic to handle during procedures.

Miniaturization of semirigid ureteroscopes has occurred. Richard Wolf produces an ultrathin semirigid ureteroscope, dubbed the “needlescope” that has a 4.5 Fr tip and a shaft that increases to 6.5 Fr. This ureteroscope has a single 3.3 Fr working channel and is available in 315 and 430 mm lengths. The very small distal tip facilitates cannulation of the ureteral orifice and pre-dilation rarely needed. The smaller 3.3 Fr working channel can reduce irrigation flow when a large instrument is passed. For laser lithotripsy, a small caliber fiber with a ≤270 μm core is preferred versus a larger fiber with a 365 μm core. Although initially intended as a semi-ureteroscope for children, it has gained acceptance in treating adults as well. In our hands it has proven to be robust, despite the small size, and is our primary semirigid ureteroscope (Fig. 11.9).

Flexible Ureteroscopes

The advent of small caliber flexible ureteroscopes

coupled with the holmium:YAG laser resulted in a paradigm shift in the management of upper ureteral and renal stones [8, 9]. Shock wave lithotripsy had been the primary treatment option for stones <2.0 cm in the upper tract, but now flexible ureteroscopy with holmium:YAG laser lithotripsy became a viable alternative. After their introduction, flexible ureteroscope technology improved rapidly during the late 1990s and early 2000s resulting in smaller caliber, highly flexible instruments. At present, it is simplest to divide flexible ureteroscopes into several categories: first, fiber optic or digital optics and, second, single use or reusable.

Flexible Fiber-optic Ureteroscopes

Karl Storz currently produces the Flex-X2S fiber-optic ureteroscope, which is the successor to the prior Flex-X2 and before that the Flex-X. The Flex-X2S has a 7.5 Fr tip size that expands to 8.5 Fr along the shaft. It has 270° of primary deflection both upward and downward with an 88° field of view and 3.6 Fr working channel. The tip of the working channel of the scope is lined by LaserliteTM, a durable material designed to resist damage when the laser is fired inadvertently with the tip of the fiber within the distal working channel. The primary difference between the Flex-X2 and the newer Flex-X2S is that the newer scope has double the number of fiber-optic bundles, increasing from 4000 to 8000. This results in a sharper image with less of the honeycomb effect that can be seen when fewer fiber-optic bundles are employed. Another unique aspect of the Flex-X2S is that it is available in two different shaft lengths. The standard length is 670 mm and would be used for standard adult flexible ureteroscopy. A shorter option at 450 mm is also available and is geared toward pediatric procedures. However, the 450 mm shaft length also works well for antegrade ureteroscopy during a percutaneous procedure.

Olympus recently released its latest generation flexible ureteroscope, the URF-P7. This ureteroscope incorporates many of the features of its predecessor, the URF-P6, but with a design that focused on increased durability and stronger deflection mechanism. It incorporates a 4.9 Fr tip the quickly tapers to a 7.95 Fr shaft. The working channel is 3.6 Fr and the working length is 670 mm. The manufacturer reports 275° of upward and downward deflection. While long-term durability studies are needed to validate the manufacturers claim, this scope incorporates many changes designed to prevent the problems with locking deflection that had been reported in the prior generation of Olympus ureteroscopes [11]. The tapered tip design does facilitate passage directly without the need to place it over a guidewire. This tapered tip design has facilitated office ureteroscope for the surveillance of the upper tract transitional cell carcinoma in select patients [12].

Richard Wolf offers both a single-channel and a unique dual-channel flexible fiber-optic ureteroscope. The single-channel model is named the “Viper” and has a standard 3.6 Fr working channel, 270° of upward and downward deflection, a 680 mm working length, and a tip size of 6 Fr that increases to a shaft diameter of 8.8 Fr. This permits the use in a small diameter 10/12 Fr ureteral access sheath. The dual-channel model, called the “Cobra”, has two working channels, each with 3.3 Fr. The tip of fiber-optic Cobra is 6 Fr but increases to 9.9 Fr through the shaft. This increase in overall diameter is the trade-off for having the two working channels. However, the design permits the passage of a stone basket or laser fiber through one channel and thus does not limit irrigation through the second channel. Further creative uses might entail passing a laser fiber through one channel and a stone basket through the second channel. This ureteroscope also maintains the same 270° of bidirectional deflection at the Viper (Fig. 11.10).

Flexible Digital Ureteroscopes

With manufacturers incorporating digital image sensors in flexible ureteroscopes, the digital era of flexible ureteroscopes began [13]. Current digital ureteroscopes use one of two different types of imaging chips, either the less commonly used charge-coupled device (CCD) or the more common complementary metal–oxide–semiconductor (CMOS). Both of these devices function by converting photons into electrons [14]. The digital signal is carried through the scope along wires and then converted by the image processor into the displayed image on the monitor. CMOS-based systems require less energy, run at lower temperatures, process images quicker, and are less expensive to produce as compared to CCD based. CCD is however a more mature technology and less affected by signal noise [15]. With continual improvement in technology, the expectation is further improvement in image quality, and reduction in size will occur. This is one of the fastest progressing areas of endourologic equipment.

Digital ureteroscopes offer some advantages over fiber-optic models. The “chip-on-the-tip” design eliminates the need for a separate bulky camera head that is required with fiber-optic scopes in order to display the image on the video monitor. The results in a more ergonomic setup by being lighter and less cumbersome to handle. There are no focusing dials as the digital instruments have a fixed focal length, further simplifying operation. The lighter digital ureteroscopes may result in less hand fatigue, especially during longer procedures. Reducing the number of cords from two (camera and light cord) to one helps to prevent entanglement and clutter. However, as previously discussed, each brand of digital ureteroscope requires a manufacturer-specific video processor, and therefore switching from one manufacturer to another is not simply a process of switching scopes but also requires switching video processors. With fiber-optic ureteroscopes this is simpler, as the camera head can be moved from one scope to another independent of the manufacturer.

Karl Storz manufactures the Flex-Xc, a CMOS-based flexible digital ureteroscope. It has a single 3.6 Fr working channel and a 700 mm shaft length. It is capable of 270° of bidirectional deflection with a 90° field of view. It has a built-in LED bulb for illumination. After its initial introduction, the CMOS chip was upgraded in a revision from 240 × 240 pixels to 460 × 400 pixels. The Flex-Xc has been demonstrated in bench evaluation to be highly maneuverable and out maneuvered other digital ureteroscopes in a bench model [16] (Fig. 11.11).

The latest generation Olympus flexible ureteroscope is the CMOS-based URF-V3. It has a 8.5 distal end outer diameter, a 3.6 Fr working channel, and a length of 670 mm. It provides 275° of bidirectional deflection and has a similar revised deflection mechanism as the URF-P7 designed to be more robust and avoid the prior reported problems with locked deflection [11]. At present, no clinical data regarding performance is available, but it appears to be a promising scope design and of the prior generation URF-V2.

Richard Wolf produces two flexible digital ureteroscopes, the Boa vision and the Cobra vision. The Boa vision, similar to the fiber-optic Viper, has a single 3.6 Fr working channel. It has a 6.6 Fr stainless steel tip that increases in diameter to an 8.7 Fr shaft. It has a 680 mm working length with 270° of bidirectional deflection. Like the Storz Flex-Xc, it has an integrated LED light (Fig. 11.12a). In contrast, the Cobra vision has two working channels of 3.6 and 2.4 Fr (Fig. 11.12b). The digital Cobra vision has a 5.2 Fr tip that increases to a shaft size of 9.9 Fr. It also has a 680 mm working length, 270° of bidirectional deflection, and an integrated LED light.

Fiber-optic Versus Digital Ureteroscopes

There are multiple factors to consider when comparing fiber-optic with flexible digital ureteroscopes including imaging quality, size, maneuverability, durability, and cost. With continual innovation and introduction of new products, it is a moving target to perform direct comparisons between models, but some generalizations can be made. Multiple studies have demonstrated improved image quality when comparing fiber-optic to flexible digital ureteroscopes. In one study, the Karl Storz flexible fiber-optic ureteroscope 11274AA was compared to the Olympus URF-V, a first-generation CCD-based digital ureteroscope. The authors performed 44 consecutive procedures with these two ureteroscopes; the first 22 were with the Karl Storz fiber-optic and the later 22 with the Olympus digital. The digital URF-V scored higher in a subjective measure of maneuverability and visibility. The authors also noted greater clarity, superior magnification, and a lack of a moiré effect. The digital scope was able to visualize the entire collecting system in 90.9% of cases versus 81.8% for the fiber-optic scope [17]. Humphreys reported that with the use of digital ureteroscopes pathology such as Randall’s plaques within the renal papilla, which could not have been previously visualized with fiber-optic scopes, could now be seen [13].

Stone-free rates (SFR) were compared between fiber-optic and flexible digital ureteroscopes in several studies. One study compared the Olympus URF-P5 fiber-optic ureteroscope to the digital URF-V and evaluated stone-free outcomes 1 month after flexible ureteroscopy. The SFR was comparable at 88% and 86%, respectively, but the operative times were somewhat longer with the fiber-optic ureteroscope taking an average of 53.8 min versus 44.5 min for the digital ureteroscope [18]. In another study, the Karl Storz Flex-X2 was compared to the Gyrus/ACMI DUR-D and reported similar findings. The stone clearance rates were 88.2% and 85.7%, respectively, but again the fiber-optic instrument took slightly longer to perform the procedure at a mean of 46.5 min versus 38.3 min for the digital device [19]. While it is not entirely clear why the digital ureteroscopes had shorter procedure lengths, possibilities include that the better visualization allows for more accurate targeting of the stone and that the improved ergonomics may allow the surgeon to work in a more time-efficient manner.

Limitations of Flexible Digital Ureteroscopes

While flexible digital ureteroscopes appear to have some clear advantages, there are also some drawbacks. The digital image can be disrupted during laser lithotripsy due to the wave produced from the photoacoustic effect of the holmium:YAG laser. This is seen as lines and artifacts passing through the image on the video monitor. To counter this effect manufacturers have begun to place shock-absorbing devices at the tip of the scope where the image sensor is located [20]. While this may have reduced the effect, in my experience it can still be seen even with current generation digital ureteroscopes when the laser fires close to the tip of the scope. Advancing the laser fiber further out from the tip of the scope, and thus increasing the distance between the point where the acoustic shock wave is generated and the image sensor, helps to reduce the effect. A good guideline is to keep the fiber advanced far enough that it occupies one quarter of the screen as reported by Talso [21].

Current generation flexible digital ureteroscopes have larger shaft diameters, and in some cases tip diameters, in comparison to flexible digital ureteroscopes (Table 11.2). This is primarily a limitation of the size of the digital image sensor. The larger size can limit access through a tight ureteropelvic junction (UPJ) or narrow infundibulum. In one report using the Olympus URF-V, the target stone could not be reached in approximately 10% of the procedures, but when the surgeon switched to the smaller fiber-optic URF-P5, the target was reached in all of the procedures [15]. In a bench study using the K-Box (Porges-Coloplast, Humlebæk, Denmark), fiber-optic ureteroscopes had better end-tip deflection by a median of 21° when compared to digital ureteroscopes with the exception of the digital Flex-Xc [16]. This can be a factor when trying to enter a calyx that requires a high degree of angulation. Future advances in miniaturization that allow for a smaller diameter and more compact tip designs will help to overcome these shortcomings. In the interim, it is best to have a fiber-optic backup flexible ureteroscope available if digital ureteroscopes are used as the primary instrument. If the target cannot be reached with the digital ureteroscope, then trying the fiber-optic model is prudent.

Table 11.2

Flexible fiber-optic ureteroscopes currently on the market

	Karl Storz Flex-X2	Olympus URF-P6	Richard Wolf Viper	Richard Wolf Cobra
Distal tip	7.5 Fr	4.9 Fr	6 Fr	6 Fr
Sheath diameter	8.5 Fr	7.95 Fr	8.8 Fr	9.9 Fr
Smallest UAS it fits	9.5/11.5	9.5/11.5	9.5/11.5	11/13
Number of working channels	1	1	1	2
Working channel	3.6 Fr	3.6 Fr	3.6 Fr	3.3 Fr × 2
Angulation UP	270°	275°	270°	270°
Angulation DOWN	270°	275°	270°	270°
Fits other camera systems	Yes	Yes	Yes	Yes
Working length	670 mm	670 mm	680 mm	680 mm
Viewing angle	88°	90°	90°	90°

UAS ureteral access sheath

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