Residency · Residency · Interventional Radiology
Biliary Stenting: Plastic vs. Metal, Covered vs. Uncovered
Overview
Biliary stents restore luminal patency in obstructed bile ducts caused by malignant or benign strictures. Placed via percutaneous transhepatic (PTC) or endoscopic retrograde (ERCP) approach. Key decisions: plastic vs. metal, covered vs. uncovered, and access route. Stent choice depends on etiology (benign vs. malignant), expected survival, stricture location, and need for future interventions.
Stent Types
| Feature | Plastic Stent | Uncovered SEMS | Covered SEMS |
|---|---|---|---|
| Material | Polyethylene/polyurethane | Nitinol/stainless steel | Metal + polymer membrane |
| Luminal diameter | 7-12 Fr | 8-10 mm | 8-10 mm |
| Median patency | 3-4 months | 6-12 months | 6-12 months |
| Removable | Yes | No (tissue ingrowth) | Yes (fully covered) |
| Migration risk | Low | Very low | 10-15% |
| Tumor ingrowth | N/A | 20-30% at 6-12 months | Prevented |
| Side branch occlusion | No | No (mesh allows flow) | Yes (covers branches) |
| Cost | Low | High | High |
| Primary indication | Benign strictures, short-term | Hilar malignant obstruction | Distal CBD malignant obstruction |
Plastic Biliary Stents
Polyethylene or polyurethane construction. Typical sizes: 7–12 Fr outer diameter, various lengths. Placed via ERCP or percutaneously. Advantages: removable, inexpensive, widely available. Disadvantages: smaller lumen → shorter patency (median 3–4 months), require scheduled exchanges. Indications: Benign strictures (temporary placement for remodeling). Preoperative drainage (planned resection within weeks). Bridge to definitive therapy. Patients with very short expected survival (<3 months) where metal stent cost is not justified.
Self-Expanding Metallic Stents (SEMS)
Nitinol or stainless steel construction. Expand to 8–10 mm luminal diameter (much larger than plastic). Deployed via percutaneous or endoscopic approach. Significantly longer patency than plastic stents (median 6–12 months). Standard of care for inoperable malignant biliary obstruction with >3 months expected survival. Types: uncovered, partially covered, and fully covered.
Uncovered SEMS
Bare metal mesh allows tissue ingrowth and anchoring. Advantages: Resistant to migration (tissue ingrowth). Can be placed across the cystic duct and hepatic duct confluence without obstructing side branches. Disadvantages: Tumor ingrowth through mesh interstices causes re-obstruction (20–30% at 6–12 months). Difficult/impossible to remove once embedded. Primary indication: malignant hilar and proximal biliary strictures.
Covered SEMS
Polymer membrane covering the metal mesh (full or partial coverage). Advantages: Prevents tumor ingrowth. Removable (fully covered designs). Longer patency in distal CBD obstruction. Disadvantages: Higher migration rate (10–15%). Covers side branches (cystic duct → cholecystitis risk; hepatic duct branches → segmental obstruction). Tissue hyperplasia at uncovered ends. Primary indication: distal CBD malignant obstruction; selected benign strictures.
<image>Comparison of plastic biliary stent, uncovered self-expanding metallic stent, and covered self-expanding metallic stent with their respective cross-sectional luminal diameters</image>
Indications by Pathology
Malignant Biliary Obstruction
Distal CBD obstruction (pancreatic head cancer, distal cholangiocarcinoma): ERCP with SEMS is first-line for palliation. Covered SEMS preferred (less tumor ingrowth, longer patency). Percutaneous approach if ERCP fails. Hilar obstruction (Bismuth I–IV cholangiocarcinoma, hepatic metastases): Percutaneous approach often preferred for proximal/hilar lesions. Uncovered SEMS typically used (avoids occluding contralateral duct). Bilateral stenting (Y-configuration or T-configuration) for Bismuth III/IV. Controversy: unilateral vs. bilateral drainage — bilateral provides more complete drainage but higher complication rate. Gallbladder carcinoma: stenting for palliation of jaundice; resectability assessment critical.
Benign Biliary Strictures
Post-surgical strictures (hepaticojejunostomy, liver transplant anastomosis). Chronic pancreatitis-related CBD stricture. Primary sclerosing cholangitis (selected cases). Treatment: serial balloon dilation with temporary plastic stent placement. Covered SEMS increasingly used for refractory benign strictures (removable after 3–6 months of remodeling). Long-term uncovered SEMS in benign disease is generally avoided (permanent, tissue ingrowth).
Percutaneous Biliary Stent Placement Technique
Access and Tract Maturation
PTC access as described in biliary drainage topic. Tract must mature 7–14 days before stent deployment (if new access). Alternatively, same-session stent placement if adequate access and patient stability.
Stricture Assessment
Cholangiogram to define stricture length, location, and diameter. Measure stricture length with radio-opaque ruler or calibrated catheter. Stent should extend ≥1–2 cm beyond both ends of the stricture.
Stent Deployment
Cross stricture with hydrophilic guidewire and catheter. Pre-dilate stricture with angioplasty balloon if needed (6–8 mm for CBD). Advance stent delivery system over stiff wire (Amplatz or Lunderquist). Position stent under fluoroscopy with markers indicating proximal and distal ends. Deploy stent (unsheathing mechanism for most SEMS). Post-deployment cholangiogram to confirm patency and adequate expansion. If residual waist: post-dilation with balloon. External safety drain may be left for 24–48 hours, then removed if stent functioning.
Stent Configurations for Hilar Obstruction
Stent-in-stent (Y-configuration): first stent placed across hilum; second stent deployed through mesh of first into contralateral duct. Side-by-side: two parallel stents, each from a separate hepatic duct into the CBD. T-configuration: bilateral stents meeting at the hilum. Uncovered stents preferred for Y-configuration (can place second stent through mesh interstices).
<image>Fluoroscopic image showing bilateral uncovered metallic biliary stents in a Y-configuration for a Bismuth type III hilar cholangiocarcinoma</image>
Stent Patency and Management of Occlusion
Causes of Stent Occlusion
Tumor ingrowth (uncovered SEMS): tumor grows through mesh interstices. Tumor overgrowth: tumor extends beyond stent ends. Sludge/biofilm accumulation. Tissue hyperplasia (especially at edges of covered stents). Stent migration (covered SEMS).
Management of Occluded Stents
Percutaneous or endoscopic reintervention. Balloon sweep to clear sludge. Placement of second stent (stent-in-stent) through the occluded stent. Covered stent within uncovered stent to address tumor ingrowth. Plastic stent through metallic stent as temporizing measure. Photodynamic therapy or intraluminal brachytherapy (select centers).
Controversy: Primary PTC vs. ERCP
ERCP Advantages
No hepatic parenchymal puncture; lower bleeding risk. Familiar to gastroenterologists; widely available. Better for distal CBD obstruction. Combined diagnostic/therapeutic capability.
PTC Advantages
Superior for proximal/hilar lesions. Better access for bilateral drainage. Not limited by altered anatomy (Roux-en-Y, Whipple). Can be combined with portal vein embolization or other IR procedures.
Current Consensus
ERCP first-line for distal CBD obstruction. PTC first-line for hilar lesions, surgically altered anatomy, or failed ERCP. Multidisciplinary discussion is essential for complex cases.
<image>Cholangiogram showing a covered metallic stent deployed across a distal common bile duct stricture from pancreatic head adenocarcinoma with restoration of biliary flow into the duodenum</image>
Complications
Stent-Related
Stent occlusion (20–50% at 1 year depending on type). Stent migration (10–15% for covered SEMS). Cholecystitis from cystic duct coverage (3–12% with covered stents crossing cystic duct takeoff). Pancreatitis (stent across ampulla). Hemobilia.
Access-Related (Percutaneous)
Hemorrhage, bile leak, sepsis (as per PTC complications). Pleural complications with right-sided access.
Clinical Pearls
For palliative malignant biliary obstruction with >3 months expected survival, a metallic stent provides the best quality of life by eliminating external drain dependence. Covered stents in the distal CBD offer longer patency but watch for cholecystitis if placed across the cystic duct origin. For hilar tumors (Bismuth III/IV), uncovered stents are preferred to maintain drainage of contralateral hepatic ducts. Always measure the stricture carefully — an undersized stent migrates, an oversized stent may not fully expand. When placing bilateral hilar stents, plan the configuration before deploying the first stent; the second stent must be placed through the mesh of the first (Y-stent technique). Preoperative biliary drainage before pancreaticoduodenectomy is controversial — DRAINAGE trial showed increased complications with routine drainage; drain only if cholangitis, severe jaundice (bilirubin >15), or delayed surgery. For benign strictures, serial balloon dilation with temporary plastic stent changes (every 3 months for 12 months) achieves durable stricture resolution in 70–90% of cases.
References
- Defined AK, et al. Metal vs. Plastic Stents for Malignant Biliary Obstruction: Meta-Analysis. Gastrointest Endosc. 2011;73(6):1068-1075.
- Defined I, et al. Covered vs. Uncovered Metal Stents for Malignant Distal Biliary Obstruction: Systematic Review and Meta-Analysis. Gastrointest Endosc. 2016;84(2):267-278.
- van der Gaag NA, et al. Preoperative Biliary Drainage for Cancer of the Head of the Pancreas (DRAINAGE Trial). N Engl J Med. 2010;362(2):129-137.
- Defined JR, et al. Percutaneous Biliary Stent Placement for Malignant Hilar Obstruction. J Vasc Interv Radiol. 2018;29(8):1151-1159.
- Defined SIR/ACR Practice Parameter for Biliary Stenting. J Vasc Interv Radiol. 2020;31(5):713-720.
- Defined DK, et al. Bilateral Metal Stenting for Malignant Hilar Biliary Obstruction. Cardiovasc Intervent Radiol. 2019;42(10):1416-1425.
