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Metal & Long-Term Ureteral Stents

Metallic and long-term ureteral stents are specialized devices designed for prolonged ureteral drainage (12+ months) in chronic ureteral obstruction (CUO) from malignant or benign causes — reducing exchange frequency vs conventional polymer double-J stents.[1][2][3][4] Five commercial metallic devices plus one extra-anatomic bypass make up the primary options.

Rationale​

Conventional polymer DJ stents require 3–6 month exchange due to encrustation, biofilm, and loss of patency. In CUO this means multiple procedures per year, repeat anesthesia, and significant cost.

  • Metallic stents reduce exchanges from 6.3/yr to 1.4/yr vs polymer.[3]
  • Despite higher unit cost, the per-day cost is equivalent (SGD 7.82 vs 8.23, p = 0.888), and annual cost analysis shows 43% reduction ($11,183 vs $23,999/yr).[3][5]

Types​

1. Resonance (Cook Medical) — The Most-Studied​

Full-length, tightly coiled Ni-Co-Cr-Mo alloy double-pigtail (6 Fr) spanning the entire ureter.[6][7][8]

  • Drainage mechanism: no true central lumen — urine flows through the interstices between coils. In vivo, the Resonance cannot be completely occluded by extrinsic compression — even a maximally tightened constricting suture did not stop flow.[8]
  • Insertion: retrograde or antegrade; ~100% technical success.[1][6]
  • Recommended exchange: 12 months.[7]
  • Outcomes:
    • Median functional survival 11.7 mo; failure 19–35%; 0% failure for benign indications in one series.[1][9]
    • Patency 86% at 6 mo, 60% at 1 yr.[10]
    • +4 mo functional duration over polymer stents in the same patients (p < 0.0001).[11]
    • Lowest migration rate among metallic stents: 1%.[12]
  • Limitations: encrustation in 12/54 stents in one series; subcapsular hematoma in 3/25 in another; technically demanding exchanges; not recommended with active urolithiasis.[9][6][2]
  • Avoid in prostate cancer invading the bladder (HR 6.50, p = 0.015).[9]

2. Memokath-051 (PNN Medical) — Thermo-Expandable Spiral​

Segmental, thermo-expandable nitinol shape-memory spiral that covers only the strictured segment.[13][14]

  • Mechanism: pliable at room temperature (6 Fr) for insertion; expands to 24 Fr with 50–60 °C irrigation, anchoring above the stricture. Cold (≤ 10 °C) irrigation collapses the stent for removal — a unique feature.
  • NICE evaluation: cost-saving vs DJ in patients expected to need stenting for ≥ 30 months.[13]
  • Outcomes:
    • Functional duration 5.5–16.1 mo depending on series.[1][15]
    • Failure 64.6% in comparative series (highest of the three main metallic stents).[1]
    • 5-yr complication rate 72% in long-term independent review: migration 46% (highest of all metallic stents), blockage 34%, urosepsis 8%.[16]
    • Transplant ureters: mean indwelling 24.3 mo.[15]

3. Allium Ureteral Stent (URS) — Curative-Intent Covered​

Self-expanding, large-caliber, polymer-coated nitinol stent covering the strictured segment; expands to 30 Fr.[17][18]

  • Mechanism: delivered in compressed state through 12 Fr system, self-expands on deployment; PTFE / silicone polymer coating prevents tissue ingrowth and facilitates removal. Cystoscopic removal by collapsing with a grasper.
  • Curative potential for benign ureteral strictures: overall curative success (no reintervention ≥ 12 mo) 63.4%; 92.9% success for strictures ≤ 2 cm with 12–24 months of stent retention.[17]
  • Outcomes (Bian meta-analysis):[19]
    • Primary success < 1 yr: 81%.
    • Primary success > 2 yr: 65% (vs 23% for both Uventa and Memokath, p < 0.01).
    • Covered > uncovered stents at 1–2 yr (75% vs 53%, p = 0.01).
    • 3-yr primary patency 74%, secondary patency 90.4% in a 321-patient prospective cohort.[20]
  • Complications: migration 27.5%, encrustation 20%, end-stent restenosis 6.6%, infection 1.9%, fistula 1.4%.[20][18]
  • Risk factors for failure: stricture length > 2 cm; anastomotic etiology; radiation-induced strictures (3-yr primary patency only 54.7%); decreased ipsilateral GFR (migration predictor).[20][17][18]

4. Uventa (Taewoong Medical) — PTFE Membrane-Covered Mesh​

Double-layered PTFE membrane-covered self-expandable segmental metallic mesh.[21][22][23]

  • Outcomes:
    • Overall success 81.7%; primary success 64.8% at 308 d median.[23]
    • Lowest obstruction rate among metallic stents: 6%.[12]
    • Clinical success higher than Memokath-051 (82.4% vs 42.9%, p = 0.031).[21]
  • Major long-term safety concern: Kim 2016 — at median 30.9-month follow-up, 28% of ureter units experienced major complications (≥ Clavien-Dindo IIIb): ureteroarterial fistula 6%, ureteroenteric fistula 6%, ureterovaginal fistula 2%, ureteral perforation 2%, complete obstruction 10%. Risk factors: female sex, cervical cancer, stricture length ≥ 6 cm, placement ≥ 24 months (OR 20.4).[22]
  • Long-term primary success only 30% at 30.9 mo; 23% at > 2 yr in meta-analysis.[19][22]

5. Covered Metallic Ureteral Stents (CMUS) — General Category​

Encompasses Allium and some Uventa designs. Superior to uncovered at 1–2 yr (75% vs 53%, p = 0.01).[19] 321-patient prospective multicenter (Wang 2025): 3-yr primary patency 74.0%, secondary patency 90.4%, with significant QoL and renal function improvement. Radiation-induced strictures fare worse (primary patency 54.7%).[20]

Comparison Table​

FeatureResonanceMemokath-051Allium URSUventa
DesignFull-length coiled wire double-pigtailSegmental thermo-expandable spiralSegmental polymer-coated self-expandingSegmental PTFE-covered mesh
MaterialNi-Co-Cr-Mo alloyNitinolNitinol + polymerNitinol + PTFE
CoverageFull ureterStricture segmentStricture segmentStricture segment
Deployed size6 Fr24 Fr30 FrVariable
InsertionRetrograde or antegradeRetrogradeRetrogradeRetrograde
RemovalStandard cystoscopic exchangeCold water → collapsesCystoscopic collapseCystoscopic
Recommended dwell12 mo12+ mo12–24 moVariable
Median functional survival11.7 mo5.5 mo11.4 mo~10 mo
Failure rate19–35%64.6%47.8%30–70%
Migration1% (lowest)46% (highest)27.5%2.8%
ObstructionVariable34%6.6%6% (lowest)
Success 1–2 yrGood53%81% (best)51%
Success > 2 yrGood23%65% (best)23%
Major complicationsRareModerateLow-moderate28% (highest)

6. Detour Extra-Anatomic Stent (Coloplast)​

For complete ureteral obstruction where conventional stenting has failed and reconstructive surgery is not feasible.[24][25]

  • Design: self-retaining expanded-PTFE / silicone tube placed percutaneously into the kidney, tunneled subcutaneously through the abdominal wall, and sutured into the bladder → extra-anatomic nephrovesical bypass.[24][26]
  • Indications: complete obstruction with failed conventional stenting, surgery failed or not feasible, undesirable long-term nephrostomy.
  • Outcomes (Chong, n = 20 stents in 13 patients, 12 mo median): all stents draining successfully; QoL improved from 3.4 → 7.6 (p < 0.01); 7 patients died of malignant progression with functioning stents.[25][27]
  • Complications: urinary leaks requiring revision (4/20), recurrent UTI (2/20), 1 death from stent dislodgement → intra-abdominal sepsis.[25]

Indications​

  • Malignant ureteral obstruction — extrinsic compression where polymer stents fail or require excessively frequent exchanges.
  • Benign CUO — retroperitoneal fibrosis, radiation-induced strictures, post-surgical strictures, UPJ obstruction in non-reconstruction candidates.
  • Failed conventional stenting — recurrent obstruction despite polymer exchanges.
  • Patient preference — to reduce procedure frequency and improve QoL.
  • Curative intent (Allium specifically) for benign strictures ≤ 2 cm with 12–24 mo of stenting (Tian 2026).[17]
  • Palliative drainage in advanced cancer when QoL is the priority.

Contraindications & Cautions​

  • Urolithiasis — Resonance not recommended.[2]
  • Bulky intravesical disease — high intravesical pressure → stent failure.[7]
  • Prostate cancer invading bladder — significantly increased Resonance failure risk.[9]
  • Radiation-induced strictures — worse covered metallic stent outcomes (54.7% 3-yr patency).[20]
  • Long-term Uventa (≥ 24 mo) — OR 20.4 for major complications including ureteroarterial fistula.[22]

Common Complications​

ComplicationFrequencyNote
Migration1–46%Most common failure mode for segmental; Resonance lowest
Obstruction / blockage6–34%Tumor progression, mucosal hyperplasia, encrustation
Encrustation4.5–20%Rises with dwell; less common with Resonance
UTI / pyelonephritis1.5–10.9%—
Flank pain9–16%—
LUTS (frequency / urgency / dysuria)7–10%Distal-curl irritation
Hematuria10.9%Usually self-limited
Ureteroarterial fistulaUp to 6% (Uventa)Rare but life-threatening; long-term segmental stents
Difficult exchangeVariableReported with Resonance; tissue ingrowth with uncovered stents

References: [1][4][6][7][10][12][22]

Metallic vs Polymer Stents — Comparative Data​

ParameterMetallicPolymer DJ
Mean indwelling228.6 d146.1 d (p < 0.001)
Exchanges per year1.46.3
+Functional duration+4 mo (p < 0.0001)—
Annual cost (US)$11,183$23,999
12-mo patency (malignant)70% (CMUS)26% (p = 0.034)
Total complications (malignant)Lower (p < 0.05)Higher
QoL at 1 yr (malignant)Higher (p < 0.05)Lower

References: [3][5][11][28][29]

Emerging Technologies​

  • Biodegradable stents — polyurethane-magnesium alloy composites (complete degradation within 4 weeks) and biodegradable mesh stents (3–5 mo degradation) with lower UTI and encrustation in preclinical work.[30][31][32]
  • Drug-eluting biodegradable stents to deliver antimicrobial, antispasmodic, anti-encrustation, and anti-tumor agents during controlled degradation.[33][34]
  • Third-generation biodegradable designs aim to avoid the forgotten-stent syndrome entirely.[35] Most remain preclinical or in early clinical evaluation.

See also: Double-J Stent, Nephrostomy Tube (PCN), Nephroureteral Stent (PCNU), Ureterocolonic Fistula, Vascular-Urinary Fistula.

References​

1. Khoo CC, Ho C, Palaniappan V, et al. Single-Center Experience With Three Metallic Ureteral Stents (Allium URS, Memokath-051, and Resonance) for Chronic Ureteral Obstruction. Journal of Endourology. 2021;35(12):1829-1837. doi:10.1089/end.2021.0208

2. Benson AD, Taylor ER, Schwartz BF. Metal Ureteral Stent for Benign and Malignant Ureteral Obstruction. The Journal of Urology. 2011;185(6):2217-2222. doi:10.1016/j.juro.2011.02.008

3. Law YXT, Zhou A, Consigliere DT, Goh BYS, Tiong HY. Use of Metallic Ureteric Stents for Chronic Ureteric Obstruction and Its Association With Value-Based Care. Singapore Medical Journal. 2025;66(1):28-32. doi:10.4103/singaporemedj.SMJ-2021-418

4. Corrales M, Doizi S, Barghouthy Y, et al. A Systematic Review of Long-Duration Stents for Ureteral Stricture: Which One to Choose? World Journal of Urology. 2021;39(9):3197-3205. doi:10.1007/s00345-020-03544-x

5. López-Huertas HL, Polcari AJ, Acosta-Miranda A, Turk TM. Metallic Ureteral Stents: A Cost-Effective Method of Managing Benign Upper Tract Obstruction. Journal of Endourology. 2010;24(3):483-485. doi:10.1089/end.2009.0192

6. Liatsikos E, Kallidonis P, Kyriazis I, et al. Ureteral Obstruction: Is the Full Metallic Double-Pigtail Stent the Way to Go? European Urology. 2010;57(3):480-486. doi:10.1016/j.eururo.2009.02.004

7. Wah TM, Irving HC, Cartledge J. Initial Experience With the Resonance Metallic Stent for Antegrade Ureteric Stenting. Cardiovascular and Interventional Radiology. 2007;30(4):705-710. doi:10.1007/s00270-007-9043-4

8. Blaschko SD, Deane LA, Krebs A, et al. In-Vivo Evaluation of Flow Characteristics of Novel Metal Ureteral Stent. Journal of Endourology. 2007;21(7):780-783. doi:10.1089/end.2006.0315

9. Goldsmith ZG, Wang AJ, Bañez LL, et al. Outcomes of Metallic Stents for Malignant Ureteral Obstruction. The Journal of Urology. 2012;188(3):851-855. doi:10.1016/j.juro.2012.04.113

10. Asakawa J, Iguchi T, Tamada S, et al. Outcomes of Indwelling Metallic Stents for Malignant Extrinsic Ureteral Obstruction. International Journal of Urology. 2018;25(3):258-262. doi:10.1111/iju.13500

11. Chow PM, Chiang IN, Chen CY, et al. Malignant Ureteral Obstruction: Functional Duration of Metallic Versus Polymeric Ureteral Stents. PLoS One. 2015;10(8):e0135566. doi:10.1371/journal.pone.0135566

12. Khoo CC, Abboudi H, Cartwright R, El-Husseiny T, Dasgupta R. Metallic Ureteric Stents in Malignant Ureteric Obstruction: A Systematic Review. Urology. 2018;118:12-20. doi:10.1016/j.urology.2018.01.019

13. Eaton Turner E, Jenks M, McCool R, et al. The Memokath-051 Stent for the Treatment of Ureteric Obstruction: A NICE Medical Technology Guidance. Applied Health Economics and Health Policy. 2018;16(4):445-464. doi:10.1007/s40258-018-0389-3

14. Kulkarni R, Bellamy E. Nickel-Titanium Shape Memory Alloy Memokath 051 Ureteral Stent for Managing Long-Term Ureteral Obstruction: 4-Year Experience. The Journal of Urology. 2001;166(5):1750-1754.

15. Buksh O, Jar A, Khogeer A, et al. Thermoexpandable Memokath Stent: Usage and Efficacy in Ureteral and Urethral Strictures in Saudi Arabia. Urology Annals. 2024;16(1):98-103. doi:10.4103/ua.ua_160_22

16. Forster LR, Watson L, Breeze CE, et al. The Fate of Ureteral Memokath Stent(s) in a High-Volume Referral Center: An Independent Long-Term Outcomes Review. Journal of Endourology. 2021;35(2):180-186. doi:10.1089/end.2020.0542

17. Tian C, Wang Y, Bian X, et al. Therapeutic Efficacy of Allium Stent Combined With Balloon Dilation as a Curative Modality for Benign Ureteral Strictures. International Journal of Surgery. 2026. doi:10.1097/JS9.0000000000003899

18. Su B, Hu W, Xiao B, et al. Long-Term Outcomes of Allium Ureteral Stent as a Treatment for Ureteral Obstruction. Scientific Reports. 2024;14(1):21958. doi:10.1038/s41598-024-73125-0

19. Bian X, Hu H, Tian C, et al. Comparison of Different Segmental Metal Ureteral Stents as Maintenance Therapy Across Different Years in Ureteral Stricture Management: A Systematic Review and Meta-Analysis. International Journal of Surgery. 2025. doi:10.1097/JS9.0000000000002384

20. Wang M, Zhu R, Lai S, et al. Covered Metal Ureteral Stents in the Maintenance Treatment of Refractory Ureteral Stricture: A Prospective, Multi-Center, Large-Scale Cohort Study With 3-Year Outcomes. Journal of Endourology. 2025. doi:10.1177/08927790251378453

21. Kim KS, Choi S, Choi YS, et al. Comparison of Efficacy and Safety Between a Segmental Thermo-Expandable Metal Alloy Spiral Stent (Memokath 051) and a Self-Expandable Covered Metallic Stent (Uventa) in the Management of Ureteral Obstructions. Journal of Laparoendoscopic & Advanced Surgical Techniques. 2014;24(8):550-555. doi:10.1089/lap.2014.0056

22. Kim M, Hong B, Park HK. Long-Term Outcomes of Double-Layered Polytetrafluoroethylene Membrane-Covered Self-Expandable Segmental Metallic Stents (Uventa) in Patients With Chronic Ureteral Obstructions: Is It Really Safe? Journal of Endourology. 2016;30(12):1339-1346. doi:10.1089/end.2016.0462

23. Chung KJ, Park BH, Park B, et al. Efficacy and Safety of a Novel, Double-Layered, Coated, Self-Expandable Metallic Mesh Stent (Uventa) in Malignant Ureteral Obstructions. Journal of Endourology. 2013;27(7):930-935. doi:10.1089/end.2013.0087

24. Lloyd SN, Tirukonda P, Biyani CS, Wah TM, Irving HC. The Detour Extra-Anatomic Stent — a Permanent Solution for Benign and Malignant Ureteric Obstruction? European Urology. 2007;52(1):193-198. doi:10.1016/j.eururo.2006.11.008

25. Chong JJY, Kum F, Hadjipavlou M, et al. Extra-Anatomic Stents in Ureteric Obstruction: Our Experience. Journal of Endourology. 2019;33(3):242-247. doi:10.1089/end.2018.0610

26. Nissenkorn I, Gdor Y. Nephrovesical Subcutaneous Stent: An Alternative to Permanent Nephrostomy. The Journal of Urology. 2000;163(2):528-530. doi:10.1016/s0022-5347(05)67917-7

27. Wang Y, Wang G, Hou P, et al. Subcutaneous Nephrovesical Bypass: Treatment for Ureteral Obstruction in Advanced Metastatic Disease. Oncology Letters. 2015;9(1):387-390. doi:10.3892/ol.2014.2679

28. Kim ET, Yang WJ, Shin JH, et al. Comparison of a Covered Metallic Ureteral Stent and a Double-J Stent for Malignant Ureteral Obstruction in Advanced Gastric Cancer. Clinical Radiology. 2021;76(7):519-525. doi:10.1016/j.crad.2021.02.016

29. Chen Y, Liu CY, Zhang ZH, et al. Malignant Ureteral Obstruction: Experience and Comparative Analysis of Metallic Versus Ordinary Polymer Ureteral Stents. World Journal of Surgical Oncology. 2019;17(1):74. doi:10.1186/s12957-019-1608-6

30. Wang Y, Ren X, Ji C, et al. A Modified Biodegradable Mesh Ureteral Stent for Treating Ureteral Stricture Disease. Acta Biomaterialia. 2023;155:347-358. doi:10.1016/j.actbio.2022.11.022

31. Jin L, Yao L, Yuan F, Dai G, Xue B. Evaluation of a Novel Biodegradable Ureteral Stent Produced From Polyurethane and Magnesium Alloys. Journal of Biomedical Materials Research Part B. 2021;109(5):665-672. doi:10.1002/jbm.b.34730

32. Hu K, Hou Z, Huang Y, et al. Recent Development and Future Application of Biodegradable Ureteral Stents. Frontiers in Bioengineering and Biotechnology. 2024;12:1373130. doi:10.3389/fbioe.2024.1373130

33. Shan H, Cao Z, Chi C, et al. Advances in Drug Delivery via Biodegradable Ureteral Stent for the Treatment of Upper Tract Urothelial Carcinoma. Frontiers in Pharmacology. 2020;11:224. doi:10.3389/fphar.2020.00224

34. Xia K, Shen X, Ang X, et al. Surface Modification of Ureteral Stents: Development History, Classification, Function, and Future Developments. Expert Review of Medical Devices. 2023;20(5):401-416. doi:10.1080/17434440.2023.2198702

35. Chew BH, Paterson RF, Clinkscales KW, et al. In Vivo Evaluation of the Third Generation Biodegradable Stent: A Novel Approach to Avoiding the Forgotten Stent Syndrome. The Journal of Urology. 2013;189(2):719-725. doi:10.1016/j.juro.2012.08.202