Ureteral strictures postureteroscopy: Can we predict or avoid this catastrophic complication?

Urolithiasis is an increasing problem worldwide, and ureteroscopy is often the leading mode of treatment due to its minimally invasive nature and high stone-free rate. Ureteral stricture after ureteroscopy is a catastrophic complication often leading to silent renal functional loss. Up to 5% of patients may develop ureteral stricture after ureteroscopy, and this incidence may be as high as 24% in patients with impacted calculi.[1] With the rampant use of ureteroscopy for larger calculi, this complication is likely to increase. The etiology of the stricture is multifactorial and could be related to patient and stone factors, but procedure and surgical factors have also been implicated. Intra-operative ureteral damage in the form of perforation, mucosal injury, or stone fragments embedded in the denuded ureteral wall are the key predictors of ureteral stricture formation. Ureteral perforation at the site of impaction increases the chance of stricture by 14 times.[2] Large stone with chronic inflammation at the stone impaction site, significant hydronephrosis, and a need for a nephrostomy tube or double-J stent increase this possibility.[3] The ubiquitous use of lasers for lithotripsy, with the probable laser thermal injury, also plays a role. Larger-calibre instruments, including ureteral access sheaths and prolonged procedure time, can cause pressure-induced ischemia, increasing ureteral mucosal damage or perforation and increasing the risk of stricture. Such strictures can form at sites away from the original stone impaction site. About 60% of strictures form at sites distant from the stone impaction site.[4] What can we do to reduce this incidence? The aim of the stone treatment is obviously to remove the stone completely and safely, without further deteriorating the kidney function. The first decision a urologist needs to make is whether the patient needs a ureteroscopy or some other form of treatment. Options such as open/laparoscopic ureterolithotomy or antegrade ureteroscopy can be employed, especially for very large (>1.5 cm) and impacted calculi, to reduce the possibility of stricture formation. Ureteroscopy for larger stones has a higher risk of stricture than the other two options (4.3% vs. 0%).[5] The single-session stone-free rate for ureterolithotomy was also found to be higher, but with a marginally higher morbidity.[6] Once the decision to perform ureteroscopy is made, one needs to decide on pre-ureteroscopy drainage with a stent or a nephrostomy tube. Difficulty accessing the stone due to a noncompliant ureter or an associated infection is an obvious indication for drainage, but drainage should not be performed solely for a large or impacted stone. Placing a stent can be difficult or occasionally traumatic for patients with impacted calculi. Often, the stents dilate the ureter, improve irrigation, minimize the risk of ureteral trauma, and optimize the conditions for laser lithotripsy.[7] During ureteroscopy, standard precautions such as using appropriately sized instruments, avoiding forceful dilatation, avoiding prolonged procedures, and using appropriate laser settings are very important. Procedures lasting more than 60 min may increase the risk of ischemic injury. Does the type of laser make a difference? There is a lot of debate about the choice of ideal laser for lithotripsy. Both thulium fiber laser (TFL) and holmium lasers have their pros and cons, with minor differences in intra-operative and peri-operative results, but the literature does not support one over the other regarding the risk of ureteral stricture.[8] The occurrence of stricture would depend on how the laser settings are used. The risk increases with high power and high frequency. High power delivers excessive, rapid bursts of energy, potentially causing thermal damage to the ureteral wall’s epithelial architecture and blood supply. The control over laser fibre may be low at higher frequencies due to reduced mean visual reaction time. Furthermore, the possibility of some laser bursts failing to reach the stone and being fired into the fluid or onto the ureteric wall is higher at higher frequencies.[9] Both high power and high frequency increase intra-ureteric temperature, multiply the risk of ureteric wall damage, and hence increase the risk of ureteric stricture. This can be partly mitigated by having a steady high irrigation flow (minimum 20 ml/min). The literature does not support the notion that the use of a ureteral access sheath increases the risk of ureteral stricture,[4] although it is intuitive that a large-calibre access sheath placed for a prolonged duration can lead to ischemic injury. Can pneumatic lithotripsy reduce the chance of ureteral stricture? Although the advent of lasers has dramatically reduced the use of pneumatic lithotripsy in the ureter, an interesting study comparing pneumatic to laser lithotripsy showed that the rate of ureteral stricture was higher with laser lithotripsy (1% vs. 4.9%).[10] Dis-impacting the stone from impaction site to a dilated heathy ureter by pneumatic lithotripsy and then using laser for stone dusting may be one safer option. Hence, what should a surgeon do? Start at very low joules and a low frequency, and gradually increase the settings as the case progresses. For holmium laser, 0.3–0.4 J at 10 Hz, while for TFL, 0.5–1 J at 2 Hz should be the ideal start. Begin lithotripsy at the center of the stone and then proceed toward the wall. Intermittent breaks during lithotripsy (5 s on, 5 s off) would give time to improve vision by flushing out dust and help reduce temperatures. Mechanically disengage the stone from the wall and try to push it into the dilated ureter above the stone before lithotripsy. Remove all the fragments embedded in the ureteral wall and always place a stent at the end of the procedure. O’Sullivan et al. presented a very interesting study that concluded that the post-lithotripsy denuded ureter must not remain unstented and dry. They found that 8 of 11 patients with open, draining nephrostomy tubes developed ureteral strictures, whereas none of those with closed nephrostomy tubes or stents did.[11] Although a post-ureteroscopy stent may not prevent stricture, an open-draining nephrostomy tube in the postoperative period should be avoided. Prolonged operative time in the hands of inexperienced surgeons increases the risk of stricture development.[12] Such high-risk procedures are better performed by experienced surgeons at a high-volume center. It is important to define stricture correctly. Moretto et al. have defined ureteral stricture as ureteral narrowing leading to urinary flow impairment, associated with complications (pain, infections, or reduced renal function) and/or requiring re-intervention.[4] This definition is important because not every hydronephrosis after ureteroscopy should be labeled a stricture. Persistent hydronephrosis needs follow-up, observation, and timely intervention when indicated. The follow-up for the development of a stricture needs to be prolonged. It is important to monitor the development of the stricture, as it often causes silent damage to renal function. The incidence of diagnosis of stricture increases from 0.4% in the first 6 months to 3.1% on prolonged follow-up,[4] suggesting that follow-up with ultrasonography for a minimum of 1 year and optimally 3 years is important. This should be more vigilant in patients with large, impacted calculi with significant pre-operative hydronephrosis. Finally, although the incidence of stricture after ureteroscopy is not high, this number could be substantial given the increasing incidence of urolithiasis and the growing use of ureteroscopy with laser lithotripsy. Awareness, identification of high-risk patients, intra-operative care with documentation, and vigilant post-operative follow-up and evaluation would go a long way in early identification, prompt treatment, prevention of renal damage, and avoidance of medicolegal litigations. Financial support and sponsorship: Nil. Conflicts of interest: There are no conflicts of interest.