Lateral drainage metal ureteric stent for the treatment of ‘Y‐shaped’ branch obstructive uropathy

Abstract

Objective

To evaluate the efficacy and safety of the HuaXi technique of a lateral drainage Memokath™ metal ureteric stent (MMUS; Pnn Medical A/S, Kvistgaard, Denmark) for ‘Y‐shaped’ branch obstructive incomplete duplicated collecting systems (IDCS) and intra‐pelvic branch atresia (IPBA).

Patients and Methods

Between November 2023 and December 2024, a prospective study and follow‐up observations were conducted on 20 patients who underwent MMUS placement for IDCS and IPBA at our centre. Surgical success was defined as the initially implanted stents requiring no replacement during follow‐up and maintaining unobstructed drainage, or following planned stent replacement or removal performed, there was no worsening of renal hydronephrosis in the patient.

Results

Based on the lateral drainage characteristics of the MMUS, it was selected for treating four distinct types of ‘Y‐shaped’ branch obstructive uropathy. During the 1‐year follow‐up period, the overall success rate of MMUS placement reached 85.0%. At 1 month postoperatively, hydronephrosis volume significantly decreased (mean [standard deviation (SD)] 64.2 [63.8] vs 35.6 [39.7] cm³, P = 0.028), with serum creatinine levels (mean [SD] 97.2 [57.9] vs 90.6 [54.8] μmol/L, P = 0.046) and urea nitrogen levels (mean [SD] 5.2 [1.0] vs 4.9 [0.8] mmol/L, P = 0.036) were significantly reduced, while glomerular filtration rate remained stable (mean [SD] 81.1 [23.1] vs 80.3 [22.8] mL/min/1.73 m², P = 0.083). The 1‐year postoperative outcomes were similar to those at 1 month postoperatively. During follow‐up, no patients experienced uncontrollable postoperative complications. Stent‐related complications primarily involved haematuria (15.0%). All complications resolved spontaneously after symptomatic management.

Conclusions

Short‐term follow‐up indicates that lateral drainage MMUS offers a safe and effective treatment for ‘Y‐shaped’ branch obstructive uropathy. For patients unsuitable or unwilling to undergo urinary tract reconstruction surgery, endoscopic MMUS placement provides an optimal and viable alternative.

Abbreviations

IDCS

incomplete duplicated collecting systems

IPBA

intra‐pelvic branch atresia

MMUS

Memokath™ metal ureteric stent

MUS

metal ureteric stents

Introduction

The duplicated collecting system is the most common upper urinary tract anomaly, with a prevalence of approximately 0.7–4% [1]. The majority of cases are incomplete (70%), characterised by the fusion of two independent ureters before the ureterovesical junction, resulting in a distinctive ‘Y‐shaped’ branching anatomy [2]. Generally, patients with incomplete duplicated collecting systems (IDCS) present as asymptomatic variants. Most diagnoses are established in conjunction with other urinary tract conditions such as ureteric strictures, obstructions, or reflux [3]. Current primary surgical approaches for IDCS include pyeloplasty, laparoscopic heminephrectomy, and robotic surgery [4, 5]. However, considering the invasiveness, trauma, and potential complication risks of surgery, traditional reconstructive procedures may not be suitable for all patients [6]. Furthermore, in cases of surgical failure or recurrent urinary obstruction after reconstruction, secondary reconstructive procedures are often complicated by extensive intra‐abdominal fibrous adhesions, presenting increasing surgical challenges for both surgeons and patients [7].

In recent years, the minimally invasive and safe endoscopic metal ureteric stents (MUS) placement procedure has progressively emerged as an optimal treatment option for patients unwilling or unable to undergo reconstructive surgery [8]. Compared to traditional JJ ureteric stents, large‐calibre MUS are designed to provide more efficient urine drainage, reduce the need for frequent stent replacements, and improve patients’ quality of life [8]. However, it is noteworthy that in clinical practice, we have observed that when obstruction occurs in the branch ureter in patients with IDCS, a series of MUS, such as the Allium stent [9], while adequately draining urine from the affected ureter, may obstruct the opening of the unaffected ureter at the junction of the branch ureter due to their closed‐design stent body. This impedes urine drainage from the unaffected ureter, resulting in suboptimal overall treatment outcomes. This issue also represents a core challenge in treating intra‐pelvic branch atresia (IPBA) (including bifid renal pelvis atresia and calyceal neck atresia). The challenge lies in achieving effective treatment on the affected side without compromising urine drainage on the unaffected side. Therefore, developing a new, highly effective, minimally invasive treatment technology is imperative. The Memokath™ MUS (MMUS; Pnn Medical A/S, Kvistgaard, Denmark) is a thermo‐expandable stent made of nickel‐titanium alloy, featuring a spring‐like structure [10]. In clinical practice, we first observed that beyond drainage through its main channel, the MMUS's spring coil sidewall structure provides exceptional lateral drainage capacity distinct from that of other MUS. This makes it particularly suitable for treating conditions such as IDCS and IPBA, which have ‘Y‐shaped’ branches. However, no literature has yet addressed the application of MMUS lateral drainage characteristics in treating such ‘Y‐shaped’ branch obstructive uropathy. Therefore, this study aimed to present our first‐hand clinical experience and efficacy outcomes using endoscopic MMUS placement for these cases.

Patients and Methods

Patient Selection Process and Characteristics

This clinical study was approved by the Ethics Review Committee of West China Hospital, Sichuan University (approval number: 2023‐1586) and conducted in accordance with the Declaration of Helsinki. We prospectively recruited patients with IDCS and IPBA undergoing endoscopic MMUS placement at West China Hospital, Sichuan University, from November 2023 to December 2024. Inclusion criteria were: age ≥18 years, CT urography or antegrade/retrograde urography‐confirmed IDCS or IPBA, and inability to undergo or refusal of reconstructive surgery. Exclusion criteria were: (i) uncontrolled acute or chronic UTI; (ii) inability to undergo anaesthesia or surgery due to medical contraindications or severe systemic disease; (iii) malignancy with a life expectancy of <1 year; (iv) female patients who were pregnant or menstruating. All patients participating in this study provided informed consent and signed agreements authorising the release of their clinical metrics.

Surgical Procedure

This is a case of IDCS with branch ureteric obstruction. The patient underwent surgery under general anaesthesia in the lithotomy position. After general anaesthesia, urinary tract strictures were assessed via antegrade or retrograde urogram and ureteroscopy (Fig. 1A). Subsequently, under ureteroscopic guidance, the ultra‐smooth guidewire was retrogradely advanced into both branch ureters until it exceeded the site of ureteric stricture (Fig. 1B). A marker catheter was then advanced along the affected‐side guidewire to measure the distance from the ureteric orifice to the stricture (Fig. 1C). Add 2 cm to this measurement to determine the required length of the MMUS. A 12/14‐F 35‐cm flexible ureteric sheath was advanced along the guidewire to dilate the stricture (Fig. 1D). If the sheath could not pass, the stricture was dilated using a ureteric balloon catheter. Following successful dilatation, proceed to advance the sheath retrograde along the guidewire until its tip traverses the stricture segment. Then, withdraw the inner core of the sheath. Immediately advance the pre‐prepared MMUS along the sheath until the stent tip extends beyond the sheath tip and fully covers the stenotic segment (Fig. 1E). Subsequently, withdraw the guidewire and rapidly inject no more than 30 mL sterile water at 60 °C through the sheath tail to ensure complete expansion of the stent tip. Once the distal end of the stent was fully deployed in a funnel shape and securely anchored within the stricture, promptly withdraw the sheath and stent delivery system to complete the stent placement procedure (Fig. 1F). Subsequently, perform antegrade/retrograde pyeloureterography to confirm proper positioning of the MMUS and unobstructed drainage.

Fig. 1.

Surgical procedure. (A) Anterograde pyelography via a nephrostomy tube to visualise and assess ureteric obstruction. (B) Advance the guidewire retrograde until it traverses the stenotic segment. The red arrow indicates the guidewire in the affected side; the green arrow indicates the guidewire in the unaffected side. (C) A marker catheter was used to measure the length from the ureteric orifice to the stenotic segment of the affected ureter. The red arrow indicates the marker catheter. (D) A ureteric sheath was used to dilate the stricture segment. The red arrow indicates the ureteric sheath. (E) Advance the MMUS device along the ureteric sheath. The red arrow indicates the MMUS device, while the green arrow indicates the ureteric sheath with its inner core removed. (F) Inject sterile water at 60 °C until the proximal end of the stent is fully expanded, thereby completing the placement of the MMUS.

Follow‐Up

Patients undergo regular postoperative abdominal CT scans or CT urography, routine urine and blood tests, and assessments of renal function. Hydronephrosis volume is calculated using abdominal CT imaging measurements: Hydronephrosis volume = length × width × depth × 0.523 (unit: cm³) [11]. Follow‐up appointments were scheduled for the first postoperative month, then every 3 months thereafter, for a total follow‐up period of 1 year. During follow‐up, we meticulously documented stent‐related complications and surgical failures, along with their timing. Surgical success was defined as the initially implanted stents requiring no replacement during follow‐up and maintaining unobstructed drainage, or following planned stent replacement or removal performed, there was no worsening of renal hydronephrosis in the patient (Fig. 2).

Fig. 2.

Endoscopic MMUS placement for four types of ‘Y‐shaped’ branch obstructive uropathy. (A) IDCS with branch ureteric obstruction; (B) IDCS with confluent ureteric obstruction; (C) Bifid renal pelvis atresia; (D) Calyceal neck atresia. Red arrows indicate drainage from the affected‐side MMUS main channel; blue arrows indicate lateral drainage from the unaffected‐side MMUS; green arrows indicate urine drainage between the unaffected‐side MMUS and the ureteric wall.

Statistical Analysis

All quantitative variables were treated as continuous variables and expressed as mean (SD) or median (interquartile range). Categorical variables were described by frequency and proportion, with associations analysed using chi‐square tests. Differences in continuous variables between preoperative and postoperative groups were assessed using paired t‐tests. In addition, for all quantitative parameters in both the preoperative and postoperative groups, the mean difference between the pre‐ and postoperative values, along with the corresponding 95% CI, was calculated. Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS®) version 22.0 (IBM Corp., Armonk, NY, USA), with P < 0.05 considered statistically significant.

Results

Table 1 lists the general characteristics of all patients. From November 2023 to December 2024, this study enrolled a total of 20 patients, including 15 with IDCS and five with IPBA. Regarding the patients with IDCS, nine presented with branch ureteric obstruction, with the remaining six having the obstruction in the confluent ureter. In the IPBA group, three patients were diagnosed with calyceal neck atresia, and the other two were bifid renal pelvis atresia. Procedure‐related characteristics are presented in Table 2. Among the 20 patients, the MMUS placement success rate was 95%. One patient with IDCS required long‐term nephrostomy due to simultaneous obstruction in both branch ureters, precluding the placement of MMUS stents in both affected ureters. During the 1‐year follow‐up period, two patients experienced stent migration, two patients had stent occlusion, and one patient developed stent encrustation. For all patients with stent migration, we performed endoscopic trimming and repositioning of the stents. For the patient with encrustation, ureteroscopic holmium laser lithotripsy was performed. For the two patients with stent occlusion, we performed stent replacement. Following secondary intervention for all unexpected stent cases, all MMUS maintained patency during the final follow‐up. No severe postoperative complications were observed in any patient during the follow‐up period. Some patients developed stent‐related symptoms associated with MMUS placement postoperatively. Haematuria was the most common (15%). After patients appropriately increased their water intake and underwent symptomatic management, these complications resolved spontaneously without significantly impacting their quality of life.

Table 1.

General characteristics of the patients.

Variable	Value
Number of patients, n	20
IDCS, n
Branch ureteric obstruction	9
Confluent ureteric obstruction	6
IPBA, n
Calyceal neck atresia	3
Bifid renal pelvis atresia	2
Age, years, median (IQR)	44.5 (33.0–53.0)
Body mass index, kg/m2, median (IQR)	23.1 (22.1–25.5)
Gender, n (%)
Male	13 (65.0)
Female	7 (35.0)
Side, n (%)
Left	12 (60.0)
Right	8 (40.0)
Length of atresia, cm, mean (SD)	2.1 (0.5)
Aetiology of atresia, n (%)
Urinary stones	8 (50.0)
Following urinary cancer	4 (20.0)
Following tumour radiotherapy and chemotherapy treatment	3 (15.0)
Obstetrics and gynaecology surgery	2 (10.0)
Congenital stenosis	2 (10.0)
Tuberculosis	1 (5.0)
Treatment history of urinary tract obstruction, n (%)
JJ stent	15 (75.0)
Nephrostomy	7 (35.0)
Internal incision and balloon dilatation	5 (25.0)
Operative time, min, median (IQR)	35.5 (27.0–55.5)
Hospital stay time, days, median (IQR)	4 (3–5)
Total cost, US $, median (IQR)	12702.0 (5210.5–14052.8)

IQR, interquartile range.

Table 2.

Procedure‐related characteristics.

Variable, n (%)	1 month after surgery	1 year after surgery	Total
Release of obstruction	19 (95.0)		19 (95.0)
Follow‐up success rate	18 (90.0)	17 (85.0)	17 (85.0)
Stent migration	1 (5.0)	1 (5.0)	2 (10.0)
Stent occlusion	1 (5.0)	1 (5.0)	2 (10.0)
Stent encrustation	0 (0)	1 (5.0)	1 (5.0)
Operative complications
Pain	1 (5.0)	0 (0)	1 (5.0)
Haematuria	2 (10.0)	1 (5.0)	3 (15.0)
UTI	0 (0)	1 (5.0)	1 (5.0)
LUTS	0 (0)	1 (5.0)	1 (5.0)

Follow‐up outcomes of the surgery are shown in Table 3. At 1 month postoperatively, patients exhibited a reduced hydronephrosis volume (mean [SD] 64.2 [63.8] vs 35.6 [39.7] cm³, P = 0.028), with serum creatinine (mean [SD] 97.2 [57.9] vs 90.6 [54.8] μmol/L, P = 0.046) and blood urea nitrogen (mean [SD] 5.2 [1.0] vs 4.9 [0.8] mmol/L, P = 0.036) levels also significantly reduced, while the GFR remained stable (mean [SD] 81.1 [23.1] vs 80.3 [22.8] mL/min/1.73 m², P = 0.083). The 1‐year postoperative outcomes were similar to those at 1 month postoperatively. These findings demonstrated the safety and efficacy of endoscopic MMUS placement in treating such ‘Y‐shaped’ branch obstructive IDCS and IPBA.

Table 3.

Follow‐up outcomes of the surgery.

Variable	Preoperative, mean (SD)	1 month after surgery, mean (SD)	MD (95% CI)	P	1 year after surgery, mean (SD)	MD (95% CI)	P
Hydronephrosis volume, cm3	64.2 (63.8)	35.6 (39.7)	−28.7 (−53.9 to −3.4)	0.028	33.1 (31.5)	−31.1 (−57.8 to −4.5)	0.025
Creatinine, μmol/L	97.2 (57.9)	90.6 (54.8)	−6.6 (−13.1 to −0.1)	0.046	87.1 (47.4)	−10.1 (−19.0 to −1.3)	0.027
Urea nitrogen, mmol/L	5.2 (1.0)	4.9 (0.8)	−0.3 (−0.6 to −0.02)	0.036	4.6 (0.6)	−0.6 (−1.0 to −0.2)	0.006
GFR, mL/min/1.73 m2	81.1 (23.1)	80.3 (22.8)	−0.8 (−8.6 to 7.0)	0.830	82.3 (21.2)	1.2 (−6.5 to 8.9)	0.744

MD, mean difference.

Discussion

For patients in good health with a potential for cure of obstructive urological diseases, urinary tract reconstruction surgery has long been regarded as the ‘gold standard’ for long‐term treatment and should be considered the first‐line approach [12]. However, it must be acknowledged that many patients face risks and challenges, such as multiple surgical failures or deteriorating health conditions, and not all patients are suitable for or willing to undergo urinary tract reconstruction surgery [13]. Among the 20 patients enrolled in this study, all had previously undergone various non‐reconstructive treatments—such as nephrostomy, JJ stent placement, endoscopic internal incision, and balloon dilatation—due to intolerance or unwillingness to undergo reconstructive surgery. These approaches yielded poor long‐term efficacy, prompting their referral to our centre. For this specific type of ‘Y‐shaped’ branch obstruction urinary tract disease, we innovatively introduced MMUS treatment for these patients and observed satisfactory outcomes. During the 1‐year follow‐up, the surgical success rate was 85% (17/20), and all renal function parameters were effectively maintained and improved. This provides an optimal and feasible treatment option for patients with ‘Y‐shaped’ branch obstructive IDCS and IPBA who are unsuitable for reconstructive surgery.

In this study, endoscopic JJ stent placement was the most frequently undergone preoperative treatment among our enrolled patients (75.0%). Previous literature has reported on the application of JJ stents in treating acute IDCS [4]. Although JJ stents achieve effective drainage in the short term, their slender diameter and flexible material make them susceptible to occlusion induced by external compression, necessitating replacement every 3–6 months. These significant drawbacks have limited the further clinical application of JJ stents [14]. With advances in materials science and increasingly refined ureteric stent design concepts, MUS have emerged as a more efficient and durable urinary drainage solution [8]. Commonly used MUS in clinical practice include Allium, Uventa, Resonance, and MMUS [9, 15]. However, it is important to note that, unlike the MMUS, the other three common MUS feature a fully enclosed structure, relying solely on the hollow lumen within the stent for drainage. The self‐expanding Allium stent, for instance, features a biocompatible membrane composed of a polyurethane surface coating applied to both its inner and outer layers [14]. The Uventa stent shares a similar design philosophy with the Allium stent, both employing a sandwich‐type structure. However, unlike the membrane‐metal mesh‐membrane configuration of the Allium stent, the Uventa stent consists of inner and outer layers of self‐expanding nickel‐titanium alloy mesh covering an intermediate layer of polytetrafluoroethylene [16]. The Resonance stent resembles a JJ ureteric stent in shape, featuring an entirely enclosed metal coil structure throughout [17]. Although the clinical efficacy of these three stents in treating urinary tract obstruction has been fully demonstrated [8], the closed stent design clearly fails to accommodate the unique anatomical structure of ‘Y‐shaped’ branch obstructions such as IDCS and IPBA. Implantation may even result in suboptimal overall therapeutic outcomes.

To address the limitations of MUS in treating ‘Y‐shaped’ branch obstructive uropathy, we conducted further experiments and explorations into the structure and materials of various MUS. We observed that the thermo‐expandable MMUS, while enabling effective drainage through the main channel, also provides exceptional lateral drainage due to its spring‐coil stent structure. This feature allows it to demonstrate unique advantages over other MUS in treating ‘Y‐shaped’ branch obstructive uropathy. A case report by Chen et al. [18] on the treatment of calyceal neck atresia using MMUS further supports our findings. Nearly 1 year after stent placement, the patient demonstrated significant improvement in all renal functions, with serum creatinine levels dropping to less than half of the preoperative values. Regrettably, however, the authors in that study appear to have overlooked the role of the MMUS lateral drainage mechanism in treating patients with renal pelvic neck obstruction. Their use of MMUS for this calyceal neck atresia case was primarily driven by considerations of the stent's thermo‐responsive shape‐memory and compliance characteristics.

To further evaluate the efficacy and feasibility of the HuaXi technique of lateral drainage MMUS for treating ‘Y‐shaped’ branch obstructive uropathy, we conducted a large‐scale cohort study and follow‐up observation of patients enrolled between November 2023 and December 2024. Among 20 patients with ‘Y‐shaped’ branch obstructive uropathy, the 1‐year success rate of MMUS placement was 85.0%. During the 1‐year follow‐up period, we observed that endoscopic MMUS placement yielded satisfactory outcomes for four types of ‘Y‐shaped’ branch obstructive uropathy, without compromising drainage on the unaffected side or overall therapeutic efficacy. All patients demonstrated significant postoperative improvement in hydronephrosis, serum creatinine, and blood urea nitrogen levels, while GFR remained stable without further deterioration. Regarding complications following stent placement, no severe postoperative complications were observed in any patient throughout the follow‐up period. All stent‐related complications were effectively resolved with symptomatic management. However, it is unignorable that in this study, three patients experienced non‐replacement adjustments to their stents (two cases of stent migration and one case of stent encrustation). Although all three non‐replacement adjustments did not affect clinical outcomes or prognosis, and all patients completed at least 1‐year follow‐up, this does not mean we can overlook the risk of surgical failure associated with stent migration or encrustation. Particularly regarding stent migration, compared to other MUS, stent migration is a more common adverse event with the MMUS [10]. Therefore, as surgeons, we must clearly recognise the importance of precise proximal stent positioning during surgery and of managing patients’ postoperative behaviour to avoid recurrence or complete stent migration, which would necessitate stent replacement or removal.

Notably, regarding the drainage mechanism of MMUS, compared to the other three conditions, patients with IDCS with confluent ureteric obstruction achieve urinary drainage solely through the main channel of the MMUS itself, without interference from any branch ureteric structures. In contrast, in the other three scenarios, the urine from the affected side is fully drained through the MMUS's main channel. For the unaffected side, the MMUS's coil‐like structure does not obstruct drainage; urine from the unaffected side flows along the coil structure into the main channel, achieving substantial lateral drainage. Furthermore, the MMUS has a diameter of only 10.5 F, slightly smaller than the normal ureteric diameter [19]. Following MMUS placement, normal ureteric peristalsis remains undisturbed. Moreover, the appropriately sized diameter of the MMUS provides a protective effect in reducing the risk of secondary ischaemic injury to the ureteric wall [16]. Consequently, we further hypothesised that a small portion of urine from the unaffected side may still flow through the gap between the stent and the ureteric wall.

Although this study provides new insights into the treatment of ‘Y‐shaped’ branch obstructive uropathy, including IDCS and IPBA, several limitations remain. First, as a single‐centre prospective study lacking multicentre controls, its findings may not be directly generalisable to other centres or patient populations. Furthermore, given the relative rarity of the disease state, the sample size enrolled in this study was relatively small. Moreover, our investigation on the lateral drainage mechanism of MMUS focused solely on IDCS with unilateral ureteric obstruction and patients with isolated calyceal neck or bifid renal pelvis atresia. For duplicated collecting systems, multiple calyceal necks, or multiple‐branch renal pelvis obstruction, the therapeutic efficacy achievable with MMUS may be relatively limited. Finally, longer‐term follow‐up is required to evaluate the long‐term therapeutic efficacy of MMUS placement. These areas represent key directions for continued effort and in‐depth research at our centre.

Conclusion

In summary, lateral drainage MMUS is a safe and effective treatment for ‘Y‐shaped’ branch obstructive IDCS and IPBA. For patients unsuitable or unwilling to undergo urinary tract reconstruction surgery, endoscopic MMUS placement offers an optimal and viable therapeutic alternative. This approach effectively avoids surgical trauma and frequent JJ stent replacements while alleviating hydronephrosis and preserving renal function.

Author Contributions

Yixiong Zhan: writing – original draft; Yuchong He and Jixiang Chen: data curation; Jiaxin Yang: software; Fei Li and Xiaoshuai Gao: investigation; Guo Chen: Methodology, writing – review and editing; Xin Wei: supervision.

Disclosure of Interests

All authors declare no competing interests.

Ethics Approval

This prospective clinical trial was approved by the Ethics Approval Committee of West China Hospital, and the registered number is 2023‐1586.

Funding

This study was supported by the Natural Science Foundation of China (grant number: 82300789) and Sichuan University Postgraduate Education Teaching Reform Research Project (grant number: GSSCU2024093).

Clinical Trial Registration

1. Name of the registry: Chinese Clinical Trial Registry.

2. Registration identifier: ChiCTR2400079508.

3. Hyperlink to your specific registration: https://www.chictr.org.cn.