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Indications / Contraindications
Indications
- Ureteral obstruction requiring both external drainage AND ureteral stenting (eg, pyonephrosis where internal stent alone is initially insufficient)
- Bridge to definitive ureteral stent internalization — leave NUS external for monitoring/output tracking, then cap once patent
- Ureteral fistula/leak — external limb allows monitoring of fistula output
- Ureteral anastomotic stricture post-transplant or post-surgical (antegrade dilation while maintaining drainage)
- Failed retrograde ureteral stent with active obstruction requiring external monitoring
- When ureteral lumen must be maintained open AND output tracked simultaneously
Key Distinction from Double-J
NUS has an external limb exiting the skin (drainage to bag); internal limb coils in bladder. Sideholes span renal pelvis, ureter, and bladder. Can be capped to function as internal-external or left open for full external drainage.
Key Distinction from Nephrostomy
NUS traverses the ureter and has distal pigtail in bladder — provides ureteral decompression in addition to renal drainage. Standard nephrostomy drains kidney only.
Contraindications
- Uncorrectable coagulopathy (relative — same as nephrostomy)
- Non-traversable ureteral obstruction — must be able to pass wire through ureter; if impossible, standard nephrostomy first
SIR Bleeding Risk
Category 2–3. INR <1.5, Plt >50K. Wire work through ureter adds small additional risk vs standard PCN.
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Pre-Procedure Checklist
Review CT. Understand obstruction level, ureteral anatomy, stone burden. Plan calyceal access for best wire trajectory through ureter — mid/lower pole preferred for ureteral work.
Confirm ureteral traversal is feasible. Review anatomy at obstruction site. Extrinsic compression vs intrinsic stone/stricture — affects wire strategy.
Stent sizing. Typically 8 Fr. Measure ureter on CT — distance from renal pelvis to UVJ. Order correct length before starting. Typically PCNUs are sized by the length between the pigtail loops (ureter length).
Urine culture. Order if not done. Results guide antibiotic escalation if needed post-procedure.
Antibiotics. Ceftriaxone 1g IV 1h before procedure. Required — traversal through infected/obstructed system carries high bacteremia risk.
Labs. INR <1.5, Plt >50K. BMP to assess renal function.
Consent. Ureteral perforation, sepsis, hemorrhage, failure to traverse ureter, stent migration, bladder symptoms (urgency/frequency from distal coil).
NPO. Yes — minimum 4-6h (moderate sedation required).
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Relevant Anatomy
Renal Access
- Lower pole posterior calyx: Ideal for NUS — provides inline approach to ureter. This is critical; upper pole access creates a sharper angulation that makes ureteral wire work much harder.
- Approach below 12th rib, posterior axillary line — standard nephrostomy access rules apply
- Brödel's avascular zone — target zone for calyceal access
- Retrorenal colon (~10%): check CT before access
Ureteral Course
- UPJ → retroperitoneum along psoas → iliac vessel crossing → UVJ into bladder
- NUS wire must traverse entire ureter and coil in bladder — confirm by wire coiling/behavior on fluoroscopy
- NUS catheter sideholes: some in renal pelvis, some along ureter, some in bladder
- External end exits through skin with luer-lock hub for drainage bag or capping
- Instill contrast via Foley catheter (if placed) to confirm bladder position of wire tip
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Technique
Default RadCall approach · share your own below
Supplies
Ultrasound + sterile probe cover
C-arm fluoroscopy
ChloraPrep + sterile drape
1% lidocaine
21G Chiba needle
0.018-inch guidewire
AccuStick introducer set
0.035-inch Amplatz super-stiff wire
Angled hydrophilic catheter
Hydrophilic wire (Glidewire 0.035")
8–10 Fr nephroureteral catheter (Cook NUS or equivalent)
8–10 Fr dilators
Contrast + syringes
#11 scalpel
Suture (0-silk)
Drainage bag + luer-lock cap
Steps
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Renal access
Standard nephrostomy access — posterior lower pole calyx, 21G Chiba needle, 0.018" wire → AccuStick → 0.035" Amplatz wire into collecting system. Confirm wire coiled in renal pelvis on fluoroscopy. Place 7 Fr sheath at access site.
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Antegrade pyelogram
Inject dilute contrast to delineate collecting system. Identify ureter and map obstruction location. This is your roadmap — don't skip it.
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Establish safety wire
Re-introduce the Amplatz wire through the sheath and position in the renal pelvis. Thread a 0.035" Glidewire through the sheath alongside it. The Amplatz now acts as a safety wire while you negotiate the ureter with the Glidewire.
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Traverse ureter
Advance angled catheter + hydrophilic Glidewire through UPJ → down ureter → through obstruction → into bladder. Confirm wire is in bladder: wire coils freely, changes shape with patient breathing on fluoroscopy. Can instill contrast via Foley catheter to confirm bladder position (if placed), or simply inject through the angled catheter.
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Exchange for stiff wire
Critical step. Remove sheath and safety wire. Exchange hydrophilic wire for 0.035" Amplatz super-stiff wire through the angled catheter, with the wire coiled in the bladder. This stiff wire is your working wire — it provides the column strength to drive the NUS catheter through the ureter.
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Measure ureteral length
Advance a 5 Fr catheter into the bladder to the pubic symphysis. Mark catheter at skin. Pull back catheter to the renal pelvis. Mark at skin. Measure this distance = ureteral length. Select appropriately sized catheter: 22–26 cm → most adults; 28–30 cm → tall patients / long ureters; 20–22 cm → smaller patients.
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Advance NUS catheter
Serially dilate the tract if needed. Advance 8 Fr NUS catheter over the Amplatz wire. Target position: proximal pigtail/loop in renal pelvis, sideholes straddling obstruction, distal pigtail/loop in bladder. Mark skin entry site for correct catheter depth.
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Confirm position
Fluoroscopy confirms proximal coil in renal pelvis, distal coil in bladder. Inject contrast through catheter — confirms free flow and correct positioning across obstruction.
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Secure and connect
Suture external limb to skin. Connect to drainage bag. Label with date and external catheter length marking. Inform team: capping trial in 48–72h if patient stable and afebrile.
Capping Protocol
After 48-72h confirming drainage, cap external limb → functions as internal drainage. Uncap immediately if: fever, flank pain, or high output concern. Permanent capping → wait 4-6 weeks → coordinate with urology for conversion to internal double-J stent if appropriate.
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Troubleshooting
Problem
Cannot traverse ureteral obstruction
Likely cause: Tight stricture, large obstructing stone, tumor encasing ureter.
Next step: Balloon dilation of tight stricture first (4-5mm low-profile balloon), then re-attempt wire passage. If truly impassable: leave standard nephrostomy and plan rendezvous (cystoscopy + IR simultaneous) or return after decompression in 48-72h.
Problem
Wire keeps curling back in renal pelvis
Likely cause: Not enough catheter support at UPJ before advancing wire into ureter.
Next step: Advance catheter to UPJ first to provide wire purchase before advancing into ureter. Use coaxial technique — catheter leads, wire follows.
Problem
NUS catheter won't advance past stricture
Likely cause: Tight stricture or insufficient wire stiffness during advancement.
Next step: May need 10 Fr access sheath to provide better support for catheter advancement. Sequential dilation through tight stricture before advancing NUS. Confirm Amplatz wire is in bladder — not coiled in renal pelvis.
Problem
NUS catheter too short or too long
Likely cause: Pre-procedure measurement error or incorrect measurement during the procedure.
Next step: Re-measure ureter on CT before ordering catheters. Use external catheter markings and fluoroscopic landmarks to confirm depth at placement. Have alternate catheter length available in room.
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Complications
Immediate
- Ureteral injury/perforation — from aggressive wire work; avoid forcing wire through resistance
- Sepsis/bacteremia — traversal through infected obstructed system; antibiotics critical
- Hemorrhage — from renal access; same risk as standard PCN
- Bladder perforation — from aggressive wire advancement into bladder
Delayed
- Catheter occlusion — most common delayed issue; exchange if occurs
- Stent migration — proximal or distal displacement; KUB follow-up
- Vesicoureteral reflux — through catheter; generally tolerated
- Stent encrustation — exchange every 3-6 months to prevent
- Bladder symptoms — urgency/frequency from distal coil; counsel patients pre-procedure
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Post-Procedure Care
Monitoring
- KUB within 24h to confirm catheter position (proximal coil renal pelvis, distal coil bladder)
- Output monitoring: if capped, check for post-cap fever/pain → uncap immediately if either develops
- Capping trial: 48-72h post placement if patient stable and afebrile
- Vitals q30 min × 2h post-procedure
Follow-up
- Exchange: every 3-6 months (sooner if occlusion, infection, or stent-related complications)
- Internalization plan: coordinate with urology for conversion to internal double-J when appropriate
- Patient education: bladder urgency/frequency symptoms expected; drain care if left open; capping instructions
- Urine culture from initial aspirate — guide antibiotic duration
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Critical Pearls
✦
Lower pole calyx gives best inline angle to work down the ureter. This is critical for NUS. Upper pole access creates angulation that makes ureteral wire work substantially harder. Plan calyceal access with NUS in mind from the start.
✦
After traversing ureter, ALWAYS exchange hydrophilic wire for stiff Amplatz before advancing catheter. A floppy wire will buckle in the renal pelvis or ureter during catheter advancement. The Amplatz provides the column strength needed to drive the NUS catheter.
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Capping the external limb is a diagnostic test. If patient tolerates capping (no pain, no fever) → internal drainage is working. Pain or fever after capping → obstruction still present, leave open. Don't cap and forget — reassess.
✦
NUS sits in a middle ground. More than a nephrostomy, less permanent than an internal stent — ideal when you need to monitor drainage while also maintaining ureteral patency. Understand the clinical goal before placing.
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Counsel patients about bladder symptoms. The distal coil in the bladder causes urgency and frequency. This is expected — patients who aren't warned will call thinking something is wrong. Set expectations before discharge.
✦
Confirm wire in bladder — not sigmoid. Before exchanging to Amplatz, verify wire behavior on fluoroscopy. Wire coiling freely in pelvis, changing shape with respiration = bladder. Wire in a fixed loop lateral to midline = consider sigmoid. Contrast via Foley confirms.
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NUS vs Double-J vs Nephrostomy — Quick Comparison
| Feature | Nephrostomy | NUS (Internal-External) | Double-J Internal Stent |
|---|---|---|---|
| External limb | Yes | Yes | No |
| Ureteral drainage | No | Yes | Yes |
| Output monitoring | Yes | Yes (external limb) | No |
| Drainage bag required | Yes | Yes / No (can cap) | No |
| Exchange interval | 3 months | 3-6 months | 3-6 months |
| Cystoscopy for removal | No | No | Yes (or antegrade) |
| Best for | Renal drainage only | Transition / monitoring | Long-term palliation |
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References & Resources
Primary sources · Key data · Related procedures
Key Guidelines
- SIR quality improvement guidelines for PCN and ureteral stenting
- EAU guidelines on urological infections
Primary References
- Ramchandani P, Cardella JF, Grassi CJ, et al. Quality improvement guidelines for percutaneous nephrostomy. J Vasc Interv Radiol. 2003;14(9 Pt 2):S277–S281.
- Dagli M, Ramchandani P. Percutaneous nephrostomy: technical aspects and indications. Semin Intervent Radiol. 2011;28(4):424–437.
- Chitale SV, Scott-Barrett S, Ho ETS, Burgess NA. The management of ureteric obstruction secondary to malignant pelvic disease. Clin Radiol. 2002;57(12):1118–1121.