Introduction

Urolithiasis is a common disease with prevalence and incidence that are steadily increasing, especially in the Western world. Reasons for this include climate changes and modern diet with excessive intake of sodium, animal protein, and sucrose, inducing defects in ammonia excretion and leading to reduction in systemic pH, thus favoring the onset of uric acid and calcium oxalate stones. Incidence of nephrolithiasis reaches its peak between the third and fourth decades of life. The lifetime risk of stone disease is higher in men (13 %) than in women (7 %) [1, 2]. As a consequence, many people, especially the young, experience or will experience stone disease, with socioeconomic implications. Historically, ureteroscopic surgery has advanced from a mere diagnostic procedure with several limits to an accurate, complex, and highly technologic surgical operation able to navigate the entire upper collecting system, allowing for treatment of different stones even in the most complicated circumstances [3].

In the past few years, advancements in the endourological armamentarium, the downsizing of flexible ureteroscopes, the advent of digital technology, and the introduction of holmium laser lithotripters, together with the increasing number of requests for minimally invasive procedures, have made the use of both semi-rigid ureteroscopy (URS) and flexible URS for urinary calculi increasingly attractive, widespread, and better able to compete with traditional shock wave lithotripsy (SWL) and percutaneous nephrolithotomy (PCNL).

We conducted a systematic review to assess the advantages and disadvantages of URS in the treatment of urolithiasis to explore potential indications and special circumstances that all urologists may find during everyday clinical practice, such as pregnancy, obesity, bleeding diathesis, renal stones larger than 2 cm, calyceal diverticula, and kidney malformations.

Materials and methods

Search strategy and study selection

According to PRISMA guidelines [4], a systematic literature review was performed to identify articles published between 1990 and December 2013 that reported different indications and special circumstances for URS. We performed a search of the PubMed, Scopus, and Embase databases utilizing the following search terms: ureteroscopy, endoscopy, calculi, urinary stones, urolithiasis, and urinary stone treatment. We also combined these with the following search terms: obesity, obese, overweight, coagulopathy, anticoagulant, warfarin, bleeding, aspirin, coumarin, clopidogrel, thrombocytopenia, pregnancy, stones larger than 2 cm, large stones, urinary malformations, horseshoe kidney, and ectopic kidney (Fig. 1).

Fig. 1
figure 1

Flowchart for article selection process of the review

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The search was performed by two of the authors (G.G. and S.P.), independently of each other, and disagreements among the investigators were resolved by consensus. They reviewed each title and abstract, and, if unclear, the full article was reviewed, except for those reporting studies with pediatric populations, articles with less than eight cases, and articles with unclear data. Language and article-type limits were applied to exclude non-English articles, review articles, meeting abstracts, case reports, editorials, and letters. References of articles were screened to identify any missed articles.

Data extraction and assessment of results

Articles were separated into the following categories: pregnancy, obesity, bleeding diathesis, stones larger than 2 cm in diameter, calyceal diverticula, and kidney malformations. The following variables were extracted from each study for the following six categories: (1) URS and pregnancy: type of study, study population demographics, symptoms, imaging preoperative, type of anesthesia, fluoroscopy, stone size and location, method of stone extraction, operative time, stone-free rate (SFR), stent placement, and complications; (2) URS: type of study, study population demographics, stone size, operative time, SFR, complications, and hospital stay; (3) URS and bleeding diathesis: type of study, study population demographics, type of anticoagulant used or coagulopathy, stone size, operative time, SFR, complications, and hospital stay; (4) URS and stones larger than 2 cm in diameter: type of study, study population demographics, stone size, use of ureteral access sheath, operative time, primary SFR, SFR after treatment completion, number of procedures per patient, complications, and hospital stay; (5) URS and calyceal diverticula: type of study, study population demographics, symptoms, stone size, diverticulum and stone location, technique used, operative time, SFR, complications, and hospital stay; and (6) URS and kidney malformations: type of study, study population demographics, type of malformations, stone size, use of ureteral access sheath, operative time, primary SFR, SFR after treatment completion, and complications. We used a narrative synthesis for the analyses of the studies, including a description of the characteristics and main outcomes reported in the articles.

Results

URS and pregnancy

Seventeen reports of URS in pregnant women were identified in the literature search (Fig. 1; Table 1). All of these [5–15, 17–21] except one [16] were retrospective studies. These case series included 378 pregnant women undergoing URS, for a total of 382 procedures (two were bilateral). The mean age was 26 years (range 16–41), and the mean gestational period was 24 weeks (range 12–36). The most common symptom was renal colic refractory to conservative management. All studies used ultrasonographic assessment of the urinary tract as the first investigation: 172 procedures were performed using epidural/spinal anesthesia, 180 were performed using general anesthesia, and 19 were performed using local anesthetic. The type of anesthesia was not documented in nine cases.

Table 1 URS and pregnancy
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Stone location was documented in 13 studies [6–10, 12–15, 17–20]; in 30 patients, stones were not detected during URS. The location of the stone was in the proximal, middle, and distal ureter in 66, 54, and 144 women, respectively (mean stone size, 8.6 mm). During surgery, X-rays were used in 45 patients [8, 9, 16]; six studies did not report this information [12–15, 20, 21]. Basket extraction was the most popular method of stone extraction. Laser and pneumatic lithotripsy for stone fragmentation were used in 215 cases. SFR ranged from 73 to 100 %. In 10 studies, the SFR was not available. In 186 cases, ureteral stents were positioned at the end of the surgeries. The majority of procedures were performed without intraoperative complications. Postoperative complications were as follows: 14 cases of urinary tract infections, 3 cases of fever, 2 cases of sepsis, 2 cases of hematuria, 14 cases of dysuria and pain, and 4 cases of discomfort related to stent. There were five obstetric complications: two cases of premature uterine contractions managed conservatively, two cases of preterm labor managed by normal vaginal delivery, and one preterm delivery. There were no maternal or fetal deaths described. All studies except one [5], which reported one neonate with cleft lip most likely not related to the procedure, reported 100 % healthy full-term newborns.

URS and obesity

Twelve reports of URS in obese patients were identified in the literature search (Fig. 1; Table 2). All of these were retrospective studies [22–33]. Nine out of 12 case series reported control groups [24, 26–33]. A total of 629 obese patients who underwent URS were included. The mean age was 48 years (range 19–71), and the mean BMI was 41 kg/m2 (range 30–65). Only two studies mentioned the mean American Society of Anesthesiologists score, which was 2.4 [23, 30]. The mean stone size was 13.1 mm (range 4–72). A total of 523 flexible URS and 125 semi-rigid URS were performed. Mean operative time was 72 min (range 30–275), and SFR ranged from 33 to 100 %. Not all studies reported major intraoperative complications. Postoperative complications were mostly described as minor complications. Five studies defined the SFR as having no residual stones at follow-up [22, 23, 25, 28, 30]. Three studies defined the SFR as having residual fragments 2 mm or smaller [26, 33]. Two studies defined the SFR as having stones smaller than 4 mm [31, 32]. Two studies did not define the SFR status [24, 27]. In all studies that reported control groups, no statistical differences in SFR and complications among groups were detected.

Table 2 URS and obesity
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URS and bleeding diathesis

Five reports of URS in patients with bleeding diathesis were identified in the literature search (Fig. 1; Table 3). All of these were retrospective studies [34–38]. Three out of five case series reported control groups with normal clotting parameters and no use of antithrombotic therapy [36–38]. A total of 254 patients with bleeding diathesis underwent URS. The mean age was 58 years (range 35–86). The mean stone size ranged from 4 to 35 mm, and the mean operative time ranged from 23 to 145 min. Sixty-two patients were using warfarin, 157 were using aspirin, 18 were using clopidogrel, 4 were using clopidogrel in association with aspirin, and 13 patients had other reasons for coagulopathy. Only two studies mentioned the mean American Society of Anesthesiologists score, which was 2.8 [35, 36]. SFR ranged from 69 to 100 %. One study defined the SFR as having no residual stones at follow-up [34]. Four studies defined the SFR as having residual fragments of 2–3 mm or smaller [35–38]. There were three described cases of intraoperative complications, including one significant bleeding complication and two cases of poor visibility. There were 39 postoperative complications, but only seven of which were related to coagulation status. In two studies that reported control groups, no statistical differences in SFR and complications among groups were detected [36, 38]. Only one study [37] showed statistical differences in SFR between patients with bleeding diathesis and the control group (69 vs. 94 %, p = 0.04).

Table 3 URS and bleeding diathesis
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Flexible URS and renal stones larger than 2 cm in diameter

A total of 16 reports of flexible URS in patients with renal calculi larger than 2 cm in diameter were identified in the literature search (Fig. 1; Table 4). All except two [52, 54] were retrospective studies [39–51, 53]. One out of 16 case series reported a control group with PCNL [50]. A total of 777 patients were included. The mean age was 52 years (range 10–90), and the mean stone size was 32.3 mm (range 20–97). The mean operative time per procedure was 74 min (range 25–238), and the mean operative time per patient was 100 min (29–305), but not all studies reported these times. Ureteral access sheath was used in 328 of 371 (88.4 %) patients. In six studies [39, 41–43, 49, 52], five of which came from the same two groups, the authors did not use ureteral access sheath. The average primary SFR was approximately 63 % (range 31–83 %) and the average SFR after treatment completion was approximately 90 % (range 77–96.7 %), with a mean of 1.62 procedures per patient. Four studies defined the SFR as having no residual stones at follow-up [41–43, 50]; seven studies defined it as having residual fragments 1–2 mm or smaller [40, 44–46, 48, 49, 51], whereas two studies defined SFR as having stones smaller than 4 mm [52, 53]. Two studies did not define what was meant by SFR status [42, 43]. One study reported different primary SFRs related to different SFR status (0–4 mm) [47]. In 13 studies, the authors used holmium laser for stone fragmentation. Mariani [41–43] reported performing electrohydraulic lithotripsy in combination with holmium laser. In all studies, the authors assessed the SFR through several imaging methods; none used computed tomography scan as the preoperative or postoperative imaging method to detect the stone. No major intraoperative complications occurred, but seven studies did not mention the type of complications that happened. Out of 777 overall complications that occurred, there were 78 (9.9 %) postoperative complications, with minor complications developing in 41 (5.2 %) patients and major complications developing in 37 (4.7 %) patients. Mortality rate was 0 %.

Table 4 Flexible URS and stones larger than 2 cm
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URS and calyceal diverticula

A total of four reports of URS in patients with calyceal diverticula were identified in the literature search (Fig. 1; Table 5). All were retrospective studies [55–58]; one out of four case series reported a control group that underwent PCNL [56]. A total of 189 patients with calyceal diverticula underwent flexible URS. Among these studies, Koopman et al. [58] reported in their large series 22 flexible URS in combination with SWL for stones larger than 2 cm in diameter. The mean age was 43.1 years (range 18–72); in all studies except one that did not mention symptoms, 100 % patients were symptomatic before surgery. Calyceal diverticula were located in the upper pole in 107 cases, in the interpolar zone in 51 cases, and in the lower pole in 28 cases; three patients presented with multiple calyceal diverticula. All studies identified the diverticular neck through medium contrast; in two reports, the authors used the blue test technique in case of difficulties. Consequently, the authors performed dilatation or incision of the diverticular neck. When possible, the proximal coil of the ureteral stent was inserted into the diverticulum. The SFR ranged from 19 to 90 %. Patients who were symptom-free had SFR ranging from 35 to 91 %. No major intraoperative and postoperative complications were described. Auge et al. [56] showed that PCNL was superior to flexible URS regarding SFR and also regarding the rate of complications.

Table 5 Flexible URS and calyceal diverticula
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URS and kidney malformations

Three reports of URS in patients with kidney malformations were identified in the literature search (Fig. 1; Table 6). All were retrospective studies [59–61]. A total of 45 patients underwent URS. Kidney malformations described included 41 horseshoe kidneys (HSK) and four pelvic kidneys. The mean age was 42 years (range 16–69), and the mean stone size was 15.9 mm (range 3–35). The mean operative time was 86.1 min. The average primary SFR was approximately 66 % (range 53–75 %) and the average SFR after treatment completion was approximately 77.7 % (range 70–88 %), with a mean of 1.17 procedures per patient. One study defined SFR as having residual fragments smaller than 2 mm [59], whereas one defined SFR as having stones smaller than 4 mm [61]. One study did not define what was meant by SFR status [60]. No intraoperative complications occurred, but one study did not mention the type of complications [59]. Of 37 overall complications that occurred, seven (18.9 %) were postoperative complications, with minor complications developing in six (16.2 %) patients, major complications developing in one (2.7 %) patient, and 0 % mortality rate. One study did not mention any complications [59].

Table 6 Flexible URS and renal malformations
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Discussion

The past three decades have seen radical advancements in the management of urolithiasis, so that SWL, PCNL, and, recently, URS have rendered open surgery almost obsolete and only anecdotally necessary. Over this period of time, several reports have been published regarding indications, outcomes, and complications of both SWL and PCNL. However, evidence-based demonstrations of the effectiveness of URS are scarce and not significant enough to justify its use, especially in certain circumstances. This article reviews the recent literature regarding URS in special clinical scenarios in an effort to provide endourologists with exhaustive information to broaden their armamentarium with methods with the greatest chance of success and least invasiveness when treating stone patients.

URS and pregnancy

Urinary stones appear in up to 1 out of 200 pregnant women, with higher incidence during the second and third trimesters (80–90 %). As a consequence, obstetric complications such as low birth weight, preterm labor, premature delivery, and spontaneous abortion may occur [62]. URS during pregnancy represents a challenge to most urologists because of potential risks related to anesthesia and X-ray exposure [63]. The European Association of Urology guidelines still recommend temporizing measures (stenting vs. nephrostomy) as the main treatment option [64]. However, because of accelerated encrustation of urological prosthesis during pregnancy [65], a single placement is rarely enough to last until delivery and further replacements are frequently needed [12, 66]. This situation, together with improvements in endourological equipment and skills of urologists, has led URS to become a reasonable treatment modality in such complicated scenarios.

This systematic review showed the following significant findings. First, regardless of the limited utilization of X-rays (11.9 % of cases), URS during pregnancy is highly effective and has an SFR similar to that of patients who are not pregnant (range 73–100 %). It is noteworthy that this optimal result has been achieved even though the majority of procedures have been performed under local or regional anesthesia, because it is advisable to avoid general anesthesia in such patients, especially during the first two trimesters. Second, URS is safe for both mother and fetus; major complications are quite uncommon. Only 1.3 % of patients (5/378) experienced development of severe clinical situations. However, some biases can weaken the conclusion of this study. Our major concern is publication bias, because it is likely that not all urologists are keen to communicate unfavorable outcomes in such delicate patients. Moreover, given ethical implications that make randomization of such patients impossible, the evidence base is somewhat conditional.

Keeping in mind all these considerations, when conservative temporizing management of urolithiasis during pregnancy is not successful, URS represents a viable alternative provided that it is performed by experienced physicians with extreme caution to limit general anesthesia administration and radiation exposure.

URS and obesity

Obesity may become a sort of pandemic in the current century [67]. Obese people account for more than 300 million people in the Western world. It is universally acknowledged that being overweight poses a significantly higher risk of urinary stone formation because of increased urinary excretion of uric acid, oxalate, and calcium [68–70]. As a consequence, an ever-growing number of obese patients will present to our departments because of urolithiasis, challenging urologists all over the world. Obese patients may represent a real challenge because they usually have several comorbidities, with metabolic syndrome (hypertension, obesity, diabetes, and abnormal lipid levels) being the most common scenario affecting such patients. Unfortunately, SWL does not represent a viable treatment option because it has been demonstrated that its effectiveness is significantly compromised when the distance from the skin to the stone is more than 10 cm, as usually happens for those with body mass index higher than 30 [70].

For obese patients, anesthesia could represent a major concern because intubation and high-pressure ventilation may be necessary during surgery [71]. Also, carbon dioxide retention may complicate anesthesiology management in these patients [68]. Moreover, incidences of thromboembolic and cardiovascular complications are higher [72]. All of these concerns are even more relevant for prone PCNL, which is the alternative to URS in such patients. In fact, in such a position, ventilation is difficult and compression on the abdomen may compromise venous return [73]. All these factors influence the use of PCNL in obese patients, which increases the possibility of complications and ancillary maneuvers. It is clear that flexible URS may become the first treatment option for the majority of obese patients with renal stones [74]; in fact, SFR is quite high, ranging between 33 and 100 %, with an average of 87.5 %. Of note, the SFR rate was significantly higher for ureteral stones compared with renal calculi. Not all studies encountered major intraoperative complications, and only a few minor postoperative complications have been reported. Regardless, because we do know that the majority of cohorts were small in size and retrospective, we can state that URS represents the best option for the majority of obese patients with urolithiasis. Interestingly, in comparative studies, the SFR and complication rate do not differ among obese and normal-weight patients, highlighting the safety and the efficacy of URS in this specific population. Indications for flexible URS can be extended to staghorn stones provided that the holmium laser device is available.

URS and bleeding diathesis

An ever-growing number of patients experience anticoagulation or coagulopathy. This poses a dilemma because all types of surgery are highly contraindicated in such situations because preoperative normalization of coagulation is a mandatory step before surgical approach to prevent life-threatening bleeding and/or hematoma formation [75]. As such, under the guidance of a hematologist, bridging with low molecular weight heparin is usually utilized. Furthermore, thromboembolic risk during perioperative bridging with heparin is not negligible and is as high as 1–2 % [76].

URS and flexible URS can be considered the most viable treatment modalities for anticoagulated patients, in whom SWL, PCNL, and traditional surgery are contraindicated [64, 77]. According to our review, even in such difficult clinical scenarios, SFR was quite high, ranging between 69 and 100 %, with an average of 88.7 %. Of note, this good outcome has not been impaired by complications rates similar to those of non-anticoagulated patients; only eight cases (3.1 %) of significant bleeding were encountered, but blood transfusions were necessary only in two cases (0.7 %). Only one study showed statistical differences in SFR between patients with bleeding diathesis and those in the control group (69 vs. 94 %; p = 0.04) [37]. A reason for this could be that even mild intraoperative bleeding can impair operative field visibility; consequently, in such patients, digital scopes are recommended whenever available. Similarly, the holmium laser should be the lithotripsy device of choice because of its high power and hemostatic capability that may be useful for controlling minor bleeding that may occur during flexible URS in patients with bleeding diathesis. This review may be biased by the fact that all studies were retrospective in nature. As such, this leaves room for further rigorous, prospective evaluations in the future to establish the safety and cost effectiveness of this procedure.

Flexible URS and stones larger than 2 cm

Since the advent of PCNL in the early 1980s, surgical treatment of renal lithiasis has been revolutionized, superseding open surgery in the majority of calculi [78]. Since then, the management of renal stones has continued to evolve as efforts have been made to improve the SFR while reducing the invasiveness of the procedure and complications. The advent of SWL in the late 1980 s brought the utility of PCNL into question because of its invasiveness, but it soon became clear that SWL could not be considered a panacea for all stones. SWL provides SFR as high as 54 %, but the retreatment rate is high for large stones [79] and for stones located in the lower calices with unfavorable radiographic anatomy [80]. A combination of both has been recommended, but the mild improvement in SFR (66 %) has been outweighed by the need for repeat procedures and hospitalization (3.3 per patient) [79].

In the past few years, thanks to advancements in the endourological armamentarium, along with the downsizing of flexible ureteroscopes, the advent of digital technology, and the increasing number of requests for minimally invasive procedures, flexible URS for renal calculi has increasingly gained popularity among the urological community, even for stones larger than 2 cm in diameter.

Results of this review confirm that this trend of complete intracorporeal ureteroscopic nephrolithotripsy is definitely meaningful. In fact, despite low primary SFR (63 %; range 31–83 %), the final average SFR was approximately 90 % (range 77–96.7 %), with a mean of 1.62 procedures per patient. This point is crucial and should be stressed. Flexible URS and PCNL represent two different ways to solve the same problem. Flexible URS is less invasive, given the endoluminal nature of the procedure; however, in some cases, multiple hospitalizations and anesthesia are required. However, PCNL is much more effective in a single stage but is more invasive and involves a higher risk of hemorrhagic complications and other major complications. A radical change in the attitudes of urologists will be needed for the acceptance of the idea of a multistage procedure. In addition, detailed and honest patient counseling is of paramount importance so that patients have all the necessary information to allow them to choose the procedure that best fits their expectations. The drawback of a multistage procedure is definitely balanced by extremely reduced complications, with the complication rate being only as high as 9.9 % (5.2 % minor complications and 4.7 % major complications, respectively) with the absence of mortality. A key method for containing complication rates, especially septic complications, is routine use of the ureteral access sheath (88.4 % of cases, according to this review), even though long-term data regarding potential ureteral strictures developing after its use are still lacking. To minimize the septic complication rate, the following criteria have to be rigorously adhered to: (1) operate only on patients with sterile urine; (2) always try to place a ureteral access sheath; (3) always irrigate with caution while checking the continuous outflow from the ureteral access sheath; (4) do not exceed an operative time frame of 2 h; and (5) carefully observe patients during the first 6 postoperative hours (90 % of these rare but potential lethal complications occur within 6 h) [81].

One important weakness of this study is that most studies we reviewed were retrospective. Furthermore, significant discrepancies have been found regarding the definition of SFR and the concept of major and minor complications.

Flexible URS and calyceal diverticula

Calyceal diverticula are non-secretory, transitional, cell-coated cavities located within the renal parenchyma. They arise from a minor calyx during embryogenesis and usually communicate with the collecting system through a narrow infundibulum. Calyceal diverticula have an incidence of 1 %. Most are asymptomatic; however, they can be associated with flank pain, hematuria, or infection. The most common indication for surgical management of calyceal diverticula is a concomitant calculus, which is seen in 9.5–39 % of cases and represents a special concern during treatment [82]. The goal of treatment is to remove the stone and to enlarge the diverticular neck to guarantee adequate drainage of the cavity in symptomatic patients. Until the 1980s, the cornerstone of therapy was open surgery; later, minimally invasive techniques were used. Even though SWL is still usually the first choice of treatment for such events, results are disappointing because SWL fails to resolve the primum movens dilemma, which is the drainage of the diverticula, making recurrence very likely [83]. Ideal treatment should be PCNL or flexible URS. Based on the results of our review, flexible URS is the procedure of choice. In fact, provided that PCNL guarantees better SFR (>90 %), its complications rate is not negligible, reaching a significant 18 % [56]. However, flexible URS was complication-free, with a satisfying SFR of up to 81.6 %. Key procedures in flexible URS are identifying and incannulating the infundibulum of the diverticula to cut and widen the neck. Blue test technique can be extremely useful for this purpose [84]. When this is not possible, the only therapeutic solution is PCNL or laparoscopy. Significantly worse results reported by less recent series are attributable to the limitations in the mechanical workings of first-generation flexy scopes that were available at that time. Koopman et al. [58] demonstrated that, for large stones, SWL before flexible URS can be useful for achieving initial fragmentation of the stone to reduce lasertripsy time during URS.

This review demonstrates that stone-bearing calyceal diverticula represent another ideal indication when URS would be clearly superior to other available modalities. Therefore, it should be offered as a first-line treatment for symptomatic stone-bearing calyceal diverticula.

Flexible URS and renal malformations

An anomalous kidney is defined as a kidney with abnormal ascent, form, or fusion. Incidence of renal ectopia ranges from 1 in 500 to 1 in 1,200 patients [85], whereas HSK is found in approximately 1 in 666 patients [86]. Of note, incidence of urolithiasis in such patients is known to be higher than in the normal population. The ectopic position, together with its malrotation and altered anatomy of fusion abnormality with high insertion ureteric–pelvic junction, has represented a challenge for urologists for many years. Initially, SWL has been largely performed because of its minimal invasiveness. Unfortunately, the interposition of the bony pelvis, the tortuous course of the ureter, and the high insertion of the ureteric–pelvic junction in HSK resulted in low SFR and, consequently, the frequent need for additional procedures, including PCNL, open surgery, URS, and stenting [87, 88]. As such, PCNL has become the treatment of choice for HSK, offering a satisfying SFR as high as 87.5 % but with a major complication rate that is not negligible (12.5 %) [89]. However, in the case of pelvic kidney, the potential risk of damaging bowel loops that lie in between makes PCNL very challenging, and laparoscopy has been advocated to limit the risk of adjacent organ injury, thereby limiting its use to only those endourologists with laparoscopic skills [90]. With the advent of second-generation fiber optic scopes and, recently, scopes with a digital chip-on-the-tip, newer disposable devices, and holmium laser lithotripters capable of efficiently pulverizing the majority of calculi, flexible URS has emerged as a viable alternative to SWL and PCNL for all types of anomalous kidneys. Our review demonstrated SFR of 77.7 % (range 70–88 %), with a reasonable mean of 1.17 procedures per patient. Of note, major complications were encountered only in 2.7 % of cases. Improvements in flexible URS outcomes are attributable to tremendous refinements of newer generation flexible scopes with active deflection abilities, making navigation into these complex collecting systems effective and capable of exploring virtually all calyces, regardless of the anatomical difficulties typical in these patients. In other words, flexible URS represents a cornerstone of treatment for urolithiasis in complicated clinical scenarios and should always be considered before using more invasive solutions such as PCNL, laparoscopy, or open surgery.

Comment

What clearly emerges from this comprehensive review is that the “Achilles heel” of URS is the weakness of published studies, with the majority being retrospective in nature and involving small cohorts and large discrepancies regarding important parameters such as stone size, SFR, and complication rate. As such, we need a standardized universal consensus regarding the parameters of stone size (length vs. surface vs. volume), SFR (no stone vs. <2 mm vs. <4 mm), and complication rate through categorization of specific complications of URS according to the Clavien–Dindo classification. Multicentric randomized trials that define in advance the parameters to be studied should be encouraged.

Conclusion

URS and flexible URS together with intracorporeal holmium lasertripsy are effective and reliable tools capable of treating the majority of urinary stones even in the most complicated clinical scenarios and will have more fundamental roles in endourology. The key to success is avoiding starting with URS on your own. Adequate training and sharing the tricks of the trade with the experts in the field during the start-up phase are necessary. Furthermore, detailed and frank counseling of the patients is strongly encouraged to inform them not only about the minimal invasiveness but also about outcomes of the surgeons/centers and the potential for staged multiple procedures in the most difficult cases and the possibility, although rare, of major complications.

The only potential limits for worldwide dissemination of URS are cost of acquisition and maintenance of the complex endourological armamentarium, both disposable and not disposable, and the related reimbursement by a national public health care system that is much more remunerative for PCNL. A special effort by all involved companies needs to be made to allow as many urologists as possible, especially those in developing countries, and to obtain all necessary technology and costly equipment. Only in this way we will succeed in making flexible URS a routine procedure available in all urological departments and not just in a few tertiary centers.

As such … enjoy URS and ad maiora.