Ureteroscopy

Fig. 14.1

Semirigid pediatric ureteroscopes in various sizes from 4.5/6.5 Fr and varying lengths (Karl Storz, top) and Wolf (Middle and Bottom) with offset eyepieces

Eyepieces may either be “in-line” with the ureteroscope or offset. Eyepieces that are “in-line” are more ergonomic and typically allow easy introduction of the scope with greater control. Offset eyepieces require more attention to hand placement but allow for the passage of instruments directly in-line with the scope.

Much like their adult counterparts, pediatric flexible ureteroscopes all share similar features, including an optical housing unit, flexible deflection, and a working channel. Current models of flexible ureteroscopes allow deflection up to 270°, a feature that is particularly useful when approaching lower pole calculi (Fig. 14.2). Flexible ureteroscopes with an outer diameter of 7.5 Fr and inner 3.6 Fr working channels are the most commonly utilized configuration, though 7 Fr flexible ureteroscopes are available.

../images/461848_1_En_14_Chapter/461848_1_En_14_Fig2_HTML.png — Fig. 14.2

Flexible pediatric ureteroscope showing maximal deflection which can reach 270° allowing access to difficult lower pole calyces

The use of guidewires is critical to any endourologic procedure, adult or pediatric . They are used for gaining access, in dilation procedures, for straightening the ureter, stent placement, and to maintain access via the safety wire. The standard Sensor guidewire measuring 0.035 in. × 150 cm utilized in adults is often used in pediatric cases. Other options include 0.018–0.025 in. × 150 cm glidewire versions when smaller wires are needed. When placing a second wire, dual-lumen ureteral access catheters, typically 10 Fr × 50 cm, can allow rapid and safe deployment of a second wire. After gaining access, ureteral access sheaths placed to protect the ureter from repeated trauma come in 9.5/11 Fr.

Whether performing retrograde ureteropyelography or being used for access, ureteral catheters are requisites in ureteroscopy. Similar to the larger 5 Fr × 70 cm catheters used in adult patients and larger adolescent pediatric patients, pediatric urology benefits from a tailored range of ureteral stents as small as 3–4 Fr × 70 cm.

Despite miniaturization, gaining safe access for primary ureteroscopy is not always easily accomplished even while using pediatric instruments. In such cases the ureter may be dilated to allow safe navigation. Pediatric dilation is most commonly performed using 8/10 Fr coaxial dilators.

Once successfully fragmented, stones are removed with a variety of baskets with numerous configurations. Common baskets include the Zero-tip™ and Ngage® baskets ranging from 1.7–3.0 Fr (Zero-tip™ Nitinol Stone Retrieval Basket, Boston Scientific, Boston, MA, USA; Ngage® Nitinol Stone Extractor, Cook Medical, Bloomington, IN, USA) (Fig. 14.3).

../images/461848_1_En_14_Chapter/461848_1_En_14_Fig3_HTML.jpg — Fig. 14.3

Two common baskets include the Cook Ngage® Nitinol Stone Extractor (Left) and Boston Scientific Zero-Tip™ Nitinol Stone Retrieval Basket. The Ngage® allows for excellent control for basketing within the kidney while the Zero-Tip™ is favored for ureteral basketing by the authors

Prior to concluding the case, double-J ureteral stents are often deployed to facilitate continued drainage, decompression, and reduce ureteral stricture formation. An array of double-J ureteral stents are available, ranging from 3 to 6 Fr.

Contents of a basic ureteroscopic kit should include:

Ureteroscopes:
- 6/7.5 Fr semirigid ureteroscope
- 5/6.5 Fr semirigid ureteroscopes
- 7 Fr flexible ureteroscope
Endourologic working equipment:
Wires: 0.035 in Sensor™ wire, 0.018–0.025 in ZIPwire™
Ureteral dilators: 8/10 Fr coaxial dilator
Ureteral catheters in various sizes
Dual-lumen ureteral access catheter: 10 Fr
Ureteral access sheath: 9.5/11 Fr
Retrieval Devices: Zero-tip™ or Ngage® baskets as well as others
Double-J Ureteral stents: including 3–6 Fr
Irrigation device: single action pump, pressure bag, or mechanical

Technique for Lower Ureteral Calculi

Management of distal ureteral stones , defined as those located distal to the iliac vessels, is best performed via semirigid ureteroscopy due to advantages in irrigation, visualization, instrument control, and working channel diameter. To begin the procedure, a scout film should be obtained and saved prior to insertion of any instrumentation. Distal ureteral stones are difficult to visualize on fluoroscopy; however this provides documentation of any visible stone burden on plain film prior to removal.

An age-appropriate pediatric rigid cystoscope (7–12 Fr) should be inserted into the urethra and advanced into the bladder under direct vision. Panendoscopic views should be obtained to rule out an incidental bladder mass or other pathology. Both ureteral orifices should be visualized, and a safety wire (Sensor™ 0.035 in. × 150 cm PTFE/Nitinol wire with hydrophilic tip) should be inserted into the UO ipsilateral to the stone. Often, very distal stones and those right at the UVJ can make insertion of the safety wire difficult. A 5 Fr ureteral catheter can be inserted over the wire to provide stability and aid in cannulation. Alternatively, hydrophilic guidewires (ZIPwire™ 0.025–0.035 in. × 150 cm hydrophilic-coated nitinol wire) and angled tip wires can be attempted for stones which are severely impacted. After insertion of the safety wire, a 5 Fr ureteral catheter is inserted, and the wire removed so that a retrograde pyelogram can be performed (Fig. 14.4). This verifies the upper tract anatomy as well as any potential pitfalls during the case, such as submucosal passage of a wire, J-hooking of the ureter, or any other variations in anatomy. The safety wire should be reinserted and confirmed to be in the renal pelvis where it will remain until the end of the case. If a hydrophilic wire was required to pass the stone, this should be replaced with a stiffer wire prior to beginning ureteroscopy. If purulent urine returns, a ureteral stent should be placed, and the patient should return after culture-directed treatment for UTI. In the event that a ureter cannot be cannulated due to severe stone impaction, a nephroureteral stent (6–8 Fr) may be required for ureteral access.

../images/461848_1_En_14_Chapter/461848_1_En_14_Fig4_HTML.jpg — Fig. 14.4

Retrograde pyelogram is performed at the beginning of each case showing complete opacification of the left upper tract to delineate anatomy and provide confirmation of placement of working and safety wires

The bladder should be drained prior to initiating ureteroscopy. An age-appropriate pediatric semirigid ureteroscope (4.5–7.3 Fr) is then assembled and advanced alongside the safety wire to the level of the stone. Irrigation can be performed using a pressure bag or mechanical system for continuous flow or manually by an assistant using a hand pump. In some instances the ureter is too narrow to accommodate the ureteroscope requiring ureteral dilation. Practices vary by physician regarding the thresholds for ureteral dilation vs ureteral stent placement and aborting the procedure to return in 7–14 days after a period of passive ureteral dilation. If ureteral dilation is attempted, this can be accomplished using balloon dilating devices (which is controversial), ureteral dilating sheaths, and/or serial ureteral dilators. Dilation should be performed with care as the risk of ureteral perforation is increased, and dilation over the stone can cause extrusion making extraction difficult and increasing the chances of perforation, stone granuloma formation, and eventual development of ureteral stricture. The authors’ preference is to attempt dilation with an 8/10 Fr coaxial dilator if the semirigid ureteroscope does not initially pass through the UO; however, placement of a stent is favored over balloon dilation due to less tactile feedback and increased risk of stricture formation due to ureteral injury/ischemia.

For small stones, basket retrieval can be performed; however, blind basketing and applying pressure due to tight passage through the ureter should not be attempted due to the risk of ureteral perforation and/or avulsion. Larger stones will require lithotripsy which can be accomplished by a number of devices; however, Holmium:YAG laser has emerged as the standard of care for stone fragmentation. Typically, laser lithotripsy is undertaken with a 200-μ laser fiber. Multiple techniques have been described for stone fragmentation including “dusting” or “painting” of the stone, in which it is fragmented into inconsequentially small particles which then easily pass through the urine, and “cracking” the stone into several smaller pieces which are still large enough to remove with a basketing device. For dusting, low-power and high-frequency settings (0.2 J and 30–80 Hz) are preferred, and the leading edge of the stone is contacted and “painted” continuously with the laser fiber such that it disintegrates. Irrigation washes the resulting stone powder out of the field of view. The laser fiber tip should always be in vision to prevent iatrogenic ureteral trauma. Eventually with the dusting technique, the stone will become small enough that the remaining significant stone burden can be removed with a basket device which is preferred due to the ability to send the stone for analysis. For cracking of the stone, which is preferred by the authors for distal stones due to less laser time (and less chance of iatrogenic ureteral injury) and increase in the chances of achieving stone-free status, higher-power and lower-frequency settings are used. For the authors, 0.6 J and 6 Hz is a common starting setting. The power is increased to effect by a factor of 0.2–0.4 J for harder stones with minimal changes in the frequency. The center of the stone is targeted, and the stone is lasered until it cracks into several pieces.

Basket retrieval of stone fragments can be accomplished by several devices. For distal ureteral stones, the authors prefer a 0.019 in. Zero-Tip™ basket. Stone fragments are gently grasped beginning with the most distal stones (those most proximal to the scope) and are removed extracorporeally. If a stone fragment proves too large for easy extraction, it should be dropped in the ureter and fragmented further to prevent the chances of ureteral injury or avulsion. In some instances, the basket may become entrapped around the stone, and the laser fiber must be advanced through the working channel so that the stone is fragmented while still contained within the open basket. For larger children the stone fragments can be dropped into the bladder to decrease operating time; however, at least one fragment should be sent for analysis (Fig. 14.5). All stone fragments are removed and the semirigid scope is advanced up the ureter as far as can be safely achieved to assess for retropulsion of stone fragments. Some providers prefer to deploy stone-trapping devices prior to fragmentation to prevent retropulsion (Stone Cone™, NTrap®, Leslie Parachute™, Lithocatch™, Escape™, Backstop™ gel, etc.); however, with proper lasering, basketing, and irrigation techniques, this is unnecessary and often increases operating time. If there is concern that clinically significant fragments have moved to the proximal ureter or kidney, a flexible ureteroscope can be assembled for complete ureterorenoscopy.