Metal & Long-Term Ureteral Stents
Metallic ureteral stents can reduce the burden of repeated drainage procedures in selected patients with chronic obstruction. They do not guarantee patency, eliminate follow-up or replace reconstruction when a durable repair is appropriate. The permitted indication, insertion method and maximum dwell time belong to the specific device and local labeling; “metallic” does not mean that every stent may remain for 12 months or longer.[1][2]
Choosing Long-Term Drainage
Consider the cause and length of obstruction, renal function, bladder drainage, prior radiation or reconstruction, infection and stone burden, prognosis, anesthetic burden and the patient's goals. Compare a metallic stent with polymer stenting, nephrostomy and definitive repair. In malignant obstruction, the value of drainage depends on symptoms, treatment plans and expected benefit; an exchange-saving device is useful only if it continues to drain.[1][2][3]
Published cost estimates depend on local prices, anesthesia and exchange schedules. Small retrospective comparisons support the possibility of fewer procedures, but do not establish a universal annual saving or a fixed number of exchanges for every metal or polymer product.[2][3]
Device Families
| Device | Design and practical distinction | Evidence or labeling boundary |
|---|---|---|
| Resonance | Full-length coiled metal double-pigtail stent; delivered through its dedicated sheath | Current Cook IFU: temporary drainage of extrinsic ureteral obstruction in adults, with a 12-month maximum indwell; earlier intervention may be needed.[1] |
| Memokath-051 | Segmental thermo-expandable nickel-titanium spiral | NICE recommends it as an option for selected adults, with regular position monitoring and prospective outcome collection. Use the applicable IFU for deployment/removal temperatures and dwell limits.[2] |
| Allium URS | Segmental self-expanding nitinol stent with a proprietary polymer coating | Current manufacturer description lists 24–30 Fr expanded diameters and a 10 Fr delivery system. It explicitly states that a curative effect is not CE-approved; verify the local device indication and IFU.[4] |
| Uventa | Covered self-expanding segmental metallic stent | Published long-term series include serious fistulas, perforation and obstruction. Available sizes, approved use and surveillance requirements need product-specific confirmation.[5] |
| Detour / extra-anatomic nephrovesical bypass | A subcutaneous kidney-to-bladder bypass rather than a stent passing through the ureter | A salvage option in selected patients when conventional drainage or reconstruction is unsuitable; infection, leakage, dislodgement and revision remain important risks.[6] |
Resonance: Label and Handling
The alloy is nickel-cobalt-chromium-molybdenum, not a self-expanding nitinol mesh. Experimental work examined flow through and around the coil, but a small animal compression experiment cannot establish that obstruction is impossible in patients.[7]
The closed-ended stent is inserted through the supplied delivery sheath after removal of the initial catheter and wire, according to the IFU. Do not try to apply an ordinary over-the-wire polymer-stent insertion sequence to the metal coil. Avoid excessive force, bending or stretching; check final position and function.[1]
The IFU lists no known contraindications but warns about possible nickel-allergy reactions. It calls for regular follow-up and closer monitoring in patients prone to calcium encrustation. Twelve months is the maximum permitted indwell, not a promise of one year of patency. MRI is conditional, with specified scanner, gradient, SAR and scan-time limits in the IFU; it is not unrestricted MRI compatibility.[1]
Reports of failure with bulky bladder disease, cancer progression or complex benign strictures should inform selection and follow-up. They are not, by themselves, manufacturer contraindications or evidence that a whole cancer category must never receive the device.[1][8]
Memokath: Current NICE Position
NICE's 2022 recommendations, now numbered HTG651, support Memokath-051 as an option for adults with malignant obstruction and anticipated medium- or long-term survival; benign obstruction when reconstruction is unsuitable or declined; or obstruction when repeated double-J stenting is unsuitable, declined or particularly risky. NICE also requests prospective data collection and regular monitoring for migration.[2]
The evidence remains largely observational, with substantial reintervention in longer follow-up. NICE describes potential cost savings with uncertainty about device life and comparator schedules. Its economic-model assumptions are not an approved dwell-time limit, and older claims that cost savings are established after exactly 30 months should not guide an individual decision.[2]
Allium: Drainage Is Distinct From Cure
A covered segmental stent can maintain a lumen while it is present; durable patency after removal is a different outcome. A 2026 retrospective study of balloon dilation plus Allium reported success after removal in 64/101 patients, with selected follow-up and no randomized reconstruction comparator. The much higher estimate in a short-stricture/dwell-time subgroup should not be presented as the expected success for all short strictures.[9]
The manufacturer's current page explicitly distinguishes its drainage indication from an unapproved curative effect. Its linked full IFU must be checked for the actual product before use; a website statement about possible multiyear use does not authorize a universal dwell or removal protocol.[4]
Reading Outcome Comparisons
| Source | What the result can support | What it cannot establish |
|---|---|---|
| Khoo 2021, retrospective three-device experience | 76 patients underwent 129 insertion episodes. Failure occurred in 11/23 Allium, 31/48 Memokath and 11/58 Resonance episodes; follow-up and selection differed.[8] | A patient-level randomized ranking of device safety or durability |
| Bian 2025, systematic review/meta-analysis | Summarizes 31 studies and 1,660 cases, with heterogeneous definitions and substantial longer-term heterogeneity.[10] | A universal “best stent” from cross-study pooled percentages |
| Su 2024, Allium cohort | In 30 patients receiving 40 stents, migration occurred in 11/40 and encrustation in 8/40.[11] | Applying those stent-level percentages to a different 321-patient covered-stent cohort |
| Kim 2016, Uventa safety series | In 44 patients with 50 ureteral units, 14 units had major complications at median 30.9-month follow-up, including arterial, enteric and vaginal fistulas.[5] | A precise complication probability for every contemporary covered device or a safe dwell threshold below 24 months |
Primary patency, patency after a salvage procedure, freedom from another operation and patency after removal answer different questions. Report the device, unit of analysis, follow-up and definition together. Do not mix migration percentages from one cohort with patency estimates from another.[8][10][11]
Follow-Up and Failure
Before discharge, record the device, side, size, placement date, indication, planned review and exchange/removal deadline, plus the responsible service. Monitor symptoms, renal function and upper-tract drainage as appropriate. Encrustation, tissue reaction, migration, infection and progression of the underlying obstruction can require intervention before the label's maximum duration.[1][2]
Fever with obstruction, new severe flank pain, deteriorating renal function or substantial hematuria requires assessment. Recurrent or brisk hematuria in a patient with chronic ureteral instrumentation, pelvic radiation or vascular surgery warrants consideration of a vascular-urinary fistula, rather than automatic attribution to stent irritation.[5]
Extra-anatomic bypasses also require active follow-up. In a small Detour series of 13 patients receiving 20 stents, four patients required revision for leakage, two had recurrent UTI, and one died after dislodgement with intra-abdominal sepsis. These outcomes support careful salvage counseling, not a permanent maintenance-free solution.[6]
See also: Double-J Stent, Nephrostomy Tube, Nephroureteral Catheter.
References
1. Cook Medical. Resonance Metallic Ureteral Stent Set. Current product-linked instructions for use, IFU0020-18; English pp. 3–5. Instructions. Accessed September 12, 2026.
2. National Institute for Health and Care Excellence. Memokath-051 ureter stent for ureteric obstruction. HTG651, published December 7, 2022; guidance number migrated in 2025 without a change to recommendations. Current guidance.
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. Allium Medical. Ureteric stents: current product description and regulatory notice. Manufacturer page. Accessed September 12, 2026.
5. 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
6. 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
7. 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
8. 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
9. 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
10. 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
11. 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