A Customized Reinforced 8-French Ureteral Stent with End-Piece to Decrease Ureteral Obstruction and Alleviate Stent-Related Symptoms: Evaluation of 92 Patients with 319 Ureteral Stent Procedures

Introduction

Ureteral obstruction can induce renal failure, renal colic, or pyelonephritis. Chronic renal insufficiency is a barrier to several therapies, including chemotherapy. Malignant ureteral obstruction (MUO) may result from intrinsic ureteral obstruction or extrinsic compression by a primary lesion, metastases, retroperitoneal lymphadenopathy or direct tumor seeding. It is commonly caused by prostate, bladder, ovarian, cervical, colorectal, and breast cancers. However, retroperitoneal surgery and radiotherapy can also result in benign treatment-induced ureteral strictures (Figure 1). MUO may require a ureteral stent procedure (USP) with an indwelling stent. The most common method to release renal obstruction consists of the placement of an indwelling double-pigtail stent, but its adequate insertion through an obstructed ureter does not necessarily guarantee renal decompression.^1–4

Figure 1 Fluoroscopy with contrast medium injection into the ureter. (A) Distal extrinsic uretetal compression due to prostate retroperitoneal lymphadenopathy. (B) Distal extrinsic ureteral compression due to direct ovarian tumor seeding. (C) Ureteral stricture at the sacroiliac joint after vascular surgery.

Most studies have reported an approximately 25% failure rate, which hampers the management of malignant disease, and the need for repeated changing of the stent may result in a significant reduction in overall quality of life.^5–8

Previous in vitro and in vivo studies concluded that the stiffness and lumen diameter of stents are major factors in maintaining their patency. Indeed, in these studies, the average rate of stent failure with obstruction was 23.0%, and it depended on the type of stent used in [8] (Coloplast Vortek reinforced 7-French double-pigtail stents, Bard Angiomed Urosoft reinforced 7-French or 8-French double-pigtail stents, and Superglide Teleflex Medical reinforced 8-French stents). Single or tandem reinforced 8-French stents were found to be the best to avoid stent failure, and reduced the failure rate to 11.1%.^8,9

Most studies showed mean survival to be relatively short, approximately 15 months.^5–8 Of the 156 patients of a previous study with MUO, 82.1% died, with mean survival of 15.3 months after the first USP. However, the aforementioned study concluded that it was possible to improve survival by choosing a stent stiffness suitable for the patient.⁸

Double-pigtail stents are frequently implanted in the ureter in urological practice.^1–8 However, this stent is poorly tolerated, severely impairing the patients’ quality of life.^10,11 Stent-related symptoms (SRS) are largely due to bladder irritation caused by the bladder loop¹² (Figure 2A). However, the shape of the stent has not been substantially modified since its first introduction by Zimskind in 1967.¹³

Figure 2 Appearance of ureteral stents through a ureteral obstruction. (A) Double-pigtail stent. Stent-related symptoms could be largely due to bladder irritation caused by the bladder loop. (B) Customized stent with a bladder end-piece. By decreasing the amount of material within the bladder, it should be possible to attenuate the stent-related symptoms. The end-piece results in the presence of only tiny amounts of material in the bladder. (C) Customized intra-ureteral stent with an intra-ureteral end-piece. No material is visible in the bladder.

To maintain effective ureteral drainage and minimize the amount of material remaining in the bladder, we developed a customized stent. The major characteristic of this stent is replacement of the end of the double-pigtail stent that remains in the bladder by a silicone end-piece (Figure 2B).¹⁴

The first results for 64 patients were encouraging.^4,10,14–16 In a previous study, the Ureteral Stent Symptom Questionnaire (USSQ) was used for the first evaluation of the customized stent and the scores for the main domain, ‘Urinary Symptoms’ of the USSQ were significantly lower with the customized stent than with the double-pigtail stent (23.0 ± 7.0 vs. 34.4 ± 3.6; P = 0.0004).¹⁴

Tabib et al noted that the vast majority of studies on MUO were small and retrospective and that a large proportion of these studies concerned metallic stents. The heterogeneous patient population, diversity of practices, and differences in the degree of ureteral compression, limit robust comparative analysis.¹ This study, building on prior knowledge, aims to standardize MUO management through the use of the same reinforced stent, prioritizing a large lumen, and truncating the bladder part of the double-pigtail stent.

The primary aim of this study was to evaluate the efficiency of an identical reinforced 8-French stent in a consecutive series of 92 patients on the patency rate. The secondary aim was to simply compare the tolerance of the customized stent with that of the stent of the previous study.¹⁴

Materials and Methods

From September 2015 to December 2022, 92 consecutive patients in a single institution were fitted with a customized stent for ureteral obstruction. Each patient consented to participate in the study by providing a written informed consent form. The study was retrospective and non-randomized. Renal ultrasound analyses were performed at four and five months to screen for asymptomatic stent failure. Stent permeability was assessed every six months by cystoscopy under anesthesia, with contrast medium injection into the stent end-piece under fluoroscopy. Stent failure with ureteral obstruction was defined by the presence of renal colic or renal failure with increased serum creatinine or hydronephrosis confirmed by computerized tomography or ultrasound with/without pyelonephritis. Obstruction of the stents in less than six months motivated the switch to 8-French tandem stents.

Tumor Stent Selection

All patients were fitted with the same double-pigtail stent (8F, Superglide Tumor DD Ureter Stent, Teleflex Medical, Ireland). This stent was chosen for its stiffness of 5.4 N.mm⁻² and its inner diameter of 1.6 mm.¹⁷

Construction and Implantation of Customized Stents

The procedure was carried out under general or regional anesthesia and was performed by the same surgeon (BV). The length of the ureter was measured for each patient using the marks on the ureteral catheter that was introduced from the ureteral orifice up to the renal pelvis.

The double-pigtail stent (Figure 2A) was sectioned perpendicularly with the help of the mark of the ureteral catheter, ensuring that the renal loop was in the pelvis and the stent was sufficiently long to descend to the ureteral orifice. A silicone end-piece (Cisteo MEDICAL, France) was embedded at the bottom of the stent to prevent the stent from slipping (Figure 2B).

For the customized intra-ureteral stents, the double-pigtail stent was deliberately sectioned above the mark of the ureteral catheter to ensure that the bottom of the stent remained in the distal ureter and above the ureteral orifice (Figure 2C).

The stent was placed in the kidney, as for a normal double-pigtail stent, under direct vision through a ureteroscope under fluoroscopic guidance. Obstruction of the stiffest stent in less than six months led to a switch to Superglide 8-French tandem stents. Tandem stents were simultaneously pushed using two extra-stiff guides. A plain abdomen X-ray was performed postoperatively to evaluate the position of the stent (Figure 3).

Figure 3 Appearance of ureteral stents by X-Ray. (A) Double-pigtail stent. (B) Customized stent. The bladder part of the double-pigtail stent was removed and replaced by an end-piece. (C) Customized tandem stents. The bladder part of double-pigtail stents was removed and replaced by end-pieces. Tandem stents allow a lumen twice as large while the stiffness remained unchanged (D) Customized intra-ureteral stent. No material was visible in the bladder.

Questionnaires

A French translation of the USSQ was used to evaluate stent tolerance.¹⁸ The USSQ was administered to patients fitted with a customized stent who were still alive and who had not already been included in the first study.¹⁴

Statistical Analysis

The data are presented as the mean ± SD. Data were analyzed using the Wilcoxon-Mann–Whitney test. Values of p < 0.05 were considered significant.

Results

Ninety-two patients underwent retrograde ureteral stenting with a customized reinforced Superglide 8-French stent. The distribution of the type of disease is shown in Table 1.

Table 1 Distribution of the Type of Disease

Table 2 Characteristics of the 92 Patients

Table 3 Results of the Ureteral Stent Symptom Questionnaire (USSQ) for the Customized Stent. There Was No Significant Difference in USSQ Results Between the Patients of the Two Studies. The Previous Study is That Corresponding to Reference14

During the study period, 319 USPs, involving 428 ureteral units, were separately analyzed. The procedure was bilateral in 32.6% of cases and a tandem procedure was used in 21.7%. No difficulties in placing the customized stents were encountered. In all cases, the customized stents provided effective renal drainage. No dislodgment or calcification were observed during changing of the ureteral stents.

The mean duration of stenting was 5.9 ± 1.7 months and stent failure with obstruction occurred in 5.0% (16/319) of USPs after a mean of 4.7 ± 2.4 months. Half of the obstructions were observed in patients fitted with tandem stents.

Of the 92 patients, 69 had malignant disease, of whom 43 (62.3%) died, with mean survival of 29.8 ± 25.7 months after the first USP. The characteristics and USPs of the 92 patients are shown in Table 2.

Among the 92 patients, the 17 from the preliminary study were included, and their USSQ served as a control.¹⁴ Only 20 new questionnaires could be compared because 32 patients died, 16 had their stents removed or underwent urinary diversion, and seven were lost to follow-up. Thus, the results of the questionnaires were simply compared to the preliminary values, and no significant differences were noted (Table 3).

In the present study, the scores for the main domain “Urinary symptoms” were significantly lower for patients fitted with the customized intra-ureteral stent than for those fitted with customized stents (18.3 ± 4.7 vs 24.4 ± 4.9, p < 0.04).

Discussion

Retrograde stenting has been the favored approach to release kidney obstruction in cases of MUO.^1–8 Failure of retrograde stenting has been consistently reported, with an average rate of 12.7%, and shown to depend on the severity of tumor invasion of the ureteral orifice.^6–8 In our study, retrograde stenting by endoscopy was successful for all patients, but most had already been fitted with a double-pigtail stent and had complained of bladder symptoms.

With 319 USPs, this study confirms the feasibility described in previous studies.^4,10,14–16 The end-piece is a new medical device, still unused in urological practice, and appears to be usable in its current shape (Figure 4). Renal drainage and ureteral flow through the end-piece were effective six months after stenting.

Figure 4 Endoscopic appearance of the customized stent with an end-piece in the ureteral orifice. The major characteristic of the customized stent was replacement of the bladder part of the double-pigtail stent with an end-piece after adjusting the length to exactly that of the ureter of the patient. The end-piece was embedded at the bottom of the stent to prevent the stent from slipping off. Its flexible winglets allow easy movements through the urethra during insertion and removal.

The 8-French Superglide stent was chosen due to its validated stiffness (5.4 N.mm⁻²), its wide lumen (1.6 mm), and the smoothness of the tube.¹⁷ All patients were fitted with the same reinforced 8-French Superglide stent. The stent was simply modified after truncating a double-pigtail stent and adjusting its length to exactly that of the ureter.

This study is the first to include a large number of USPs (319) with the same type of stent (Superglide). Indeed, Liu et al indicated that there was a paucity of data regarding the use of reinforced polymeric stents for patients with MUO¹⁹ and Tabib et al noted that the vast majority of studies were small and retrospective, with a large number of studies related to metallic stents. Given the heterogenous patient population and diversity of practices, the authors concluded that it was difficult to truly assess the efficacy of each method.¹ This is also the first study to show such low obstruction rates (5.0%) at 4.7 months. Most studies reported a mean stent failure rate of 25% after a mean of four months.^5–8

In a previous study, the results at the start of the study were in agreement with these data (23.0%). However, stent failures decreased by the end of the study, with a rate of 13.7%, due to specific selection of reinforced 8-French Superglide stents and active screening for insidious stent obstruction.⁸

In the present study, the stent failure rate again decreased from 13.7% to 5.0%, even though the same 8-French Superglide stents were used. This improvement can be explained by the fact that repeated obstructions associated with infections lead to irritation of the urothelium and exudation of potentially obstructive debris. Indeed, Shilo et al observed that the lumen of the 8-French ureteral stent offered better patency to colloid solutions than smaller lumen stents using a mechanical ureteral model. The authors concluded that other factors, such as urine composition and viscosity, may be major contributors to stent failure.²⁰

Obstruction of the stents in less than six months motivated the switch to 8-French tandem stents. Metal-mesh and Resonance® metallic ureteral stent have been developed as alternatives to simple ureteral stents but they are expensive and evaluation of their success in extrinsic ureteral obstruction compared to double-pigtail stents is difficult.¹ To release the kidney obstruction, percutaneous nephrostomy is a procedure in which a drainage tube can be placed under sedation, but dislodgement of the tube with recurrent obstruction is common and external collecting device is required.²¹

Several studies have shown the benefits of tandem stents, with permeability close to 80% after three months.^3,19,22,23 In our study, the permeability of tandem stents was 81.0% after 4.8 months. The results appear to be better than those in other series, but our stents were reinforced. However, we observed eight stent failures in patients fitted with tandem stents, suggesting that the properties of the urine (urine composition, viscosity, chronic infection) are clearly involved in successful drainage. Indeed, several authors concluded that debris accumulation is a possible risk factor for stent failure and suggested that larger lumen stents are less likely to become occluded with debris.²⁰

According to the manufacturer, the recommended indwelling time can be up to one year for the reinforced stents used in our study. Resonance® stents can also remain safely in situ for one year, according to the manufacturer, thus decreasing the cost of the stent. However, Tabib et al suggested that larger, prospective trials are required to fully elucidate the success rates and side-effects of metallic stents, but they represent a reasonable approach to MUO after failure of single or tandem stents.¹ In our study, we chose to change the stent every six months and such consistency strengthens the power of the study.

In previous studies, the diameter of the lumen appeared to be more important than the stiffness. The diameter of the 8-French Superglide stent’s lumen was 1.6 mm, whereas that of the other stents was only 1 mm.¹⁷ Thus, the stiffness would be the only means of keeping the lumen open.^9,20 However, other characteristics are involved. Indeed, the analysis of fluid dynamics through critical regions of the stent with abrupt changes in shape using computational fluid dynamic simulations confirmed that encrustations are possible in regions of stagnant flow and showed that stent models with the smoothest possible surface are preferable.²³ The Superglide stent was therefore chosen for its stiffness, wide lumen, and smoothness because no critical regions were observed.^17,24 This choice appears to have contributed to the low rate of stent failure.

Most studies have reported short mean survival, approximately 15 months.^5–8 Of the 156 patients of the previous study, 82.1% died with mean survival of 15.3 months after the first USP.⁸ In our study, mean survival was 29 months, double the duration of the previous study.

Several authors have reported a decrease in overall survival in cases of stent failure.^3,25 Such stent failures promote renal failure and infection and can even lead to death. Yoon et al reported higher mortality for patients with renal failure⁵ and Rosenberg et al, in cases of infection.⁶ It is possible that acute renal events can severely impair the patient’s health Patients with malignant diseases are heterogeneous, with many different etiologies of infection or death. However, the observed difference in survival suggests that recurrent stent obstruction may increase the likelihood of patient death.

Several authors have questioned the survival benefit versus the high cost of certain immunotherapies.^26,27 Our study confirms that the marketing of effective ureteral stents in MUO could provide patients with a significant increase in survival for an insignificant material cost (incremental cost-effectiveness ratio estimated to be approximately €51.2/Life Year).

SRS have been widely described with double-pigtail stents and also in cases of MUO.^11,14

In the previous study, use of a customized stent significantly decreased the total score from 34.4 for a double-pigtail stent to approximately 23.0 for a customized stent for the main domain “Urinary symptoms”.¹⁴ As expected for the customized stent, there was no significant difference between the patients of our study and those of the previous study.¹⁴

For the main domain “Urinary symptoms,” Joshi et al obtained a score of 149 for a control group without a stent.¹⁸ Interestingly, the scores of patients with a customized intra-ureteral stent were higher than those of patients without a stent, even though no material was visible in the bladder. It is possible that bladder symptoms may not only be related to the stent itself but also to the pre-existing bladder disease. Indeed, Goldfarb et al observed that symptoms in patients with stents and cervical cancer were higher than those of other patients with stents without cancer.² Moreover, the USSQ is not specifically dedicated to MUO.

The end-piece leads to the presence of only a minimal amount of material in the bladder. Less material in the bladder was theorized to result in reduced SRS. Furthermore, the stent, in itself, represents an obstruction of flow in the ureter. A short length of the stent of 21.4 cm or less for an intra-ureteral stent may decrease the risk of encrustation of the stent. However, Chew et al indicated that the exact cause and origin of symptoms from ureteral stents are not precisely known. Several other factors are likely to be involved, such as vesicoureteric reflux.¹²

Limitations

Our study had several limitations. First, the heterogeneity of patients who were subjected to different treatment according to the severity of the disease may have been subject to selection bias, and the USSQ is not specifically dedicated to this pathology. Second, our study was neither prospective nor randomized, but the large number of USPs, which were performed by a single surgeon, made it possible to obtain powerful results. Third, not all types of reinforced stents were analyzed in our study, which did not take metal stents into account. However, this series of 319 USPs is the first to focus exclusively on stent failure for on the same type of stent in MUO.

Conclusion

This study is the first to include a large number of USPs for MUO with the same type of reinforced stent and the first to obtain a stent failure rate of only 5%. The design of the stent itself could potentially improve stent patency via a wide lumen and a high degree of stiffness.

It would be informative to assess the impact of the customized stent with a wide lumen and high stiffness on overall survival and SRS symptoms in patients with MUO in a prospective randomized controlled trial.