Biliary Stents: Plastic vs. Metal Options and Placement

A biliary stent is a short tube, made of plastic or metal, placed inside the bile duct to hold it open when something is blocking the normal flow of bile from the liver to the small intestine. The blockage is most often a tumor in the pancreas or bile duct itself, though benign conditions like post-surgical scarring can also squeeze the duct shut. Stenting relieves jaundice, itching, and the cascade of problems that follow when bile backs up into the bloodstream, and in many patients with advanced cancer it serves as the primary form of palliation rather than a bridge to surgery.

Why Bile Duct Obstruction Needs Intervention

Bile is produced continuously by the liver and normally drains through a network of ducts into the duodenum, where it helps digest fats. When a tumor, gallstone, or scar tissue narrows or closes off the duct, bile accumulates in the liver and spills into the blood. The result is obstructive jaundice: yellowing of the skin and eyes, dark urine, pale stools, and often intense itching. Left untreated, the backed-up bile can trigger liver damage, infection of the biliary tree (cholangitis), and progressive malnutrition because fats are no longer absorbed properly. A biliary stent restores drainage and reverses most of these effects within days.

Stents are used across a wide range of clinical scenarios. In malignant obstruction, they palliate symptoms in patients whose tumors cannot be surgically removed and, in some cases, temporarily decompress the duct before planned surgery. They also treat bile leaks after surgery or trauma, drain infected fluid collections, and manage strictures that form at the connection point after a liver transplant.¹

Plastic Versus Metal Stents

The two broad categories are plastic (polyethylene or similar polymers) and self-expandable metal stents (SEMS). Plastic stents are inexpensive, easy to place, and simple to remove or exchange. Their drawback is a narrow inner diameter, which means they clog relatively quickly. In one early comparison, plastic stents had a median patency of about 96 days, while metal stents lasted a median of 272 days before becoming blocked.² A meta-analysis pooling data from multiple trials confirmed that metal stents stay open significantly longer and are associated with fewer repeat procedures.³

Metal stents expand to a much wider diameter once deployed, which is the main reason they resist clogging longer. The trade-off is cost: a single metal stent can be several times more expensive than a plastic one. For patients expected to survive only a few weeks, a plastic stent may be perfectly adequate and avoids the higher upfront expense. For patients likely to live several months or longer, a metal stent often proves more economical overall because it reduces the need for repeat hospital visits and procedures.⁴ In some health-care settings, though, repeated plastic stent exchanges still work out cheaper over the course of treatment.⁵

When patients with pancreatic cancer need biliary drainage before starting chemotherapy, metal stents reduce the rate of re-obstruction during treatment compared with plastic stents, making them particularly useful in that setting.⁶

Covered, Uncovered, and Partially Covered Metal Stents

Metal stents come in three sub-types depending on whether a membrane wraps around the wire mesh. Uncovered stents are bare metal; the mesh sits directly against the duct wall and tissue grows through the gaps, which anchors the stent firmly but also means tumor can grow right through the mesh (tumor ingrowth). Covered stents have a polymer sleeve over the entire mesh, blocking tissue ingrowth. Partially covered stents leave the ends bare so the stent anchors itself, while the middle section is sheathed.

A meta-analysis comparing covered and uncovered designs found that covering the mesh dramatically reduced tumor ingrowth but came with its own problems. Covered stents migrated far more often and accumulated more sludge inside the lumen.⁷ Tumors also learned to grow around the ends of the cover (tumor overgrowth), partially negating the benefit. A study of partially covered stents found a similar pattern: ingrowth dropped substantially, but stent migration became significantly more common and the partially covered design did not clearly extend overall patency compared with bare metal.⁸

The practical upshot is that no single design dominates. Uncovered stents are better when anchoring matters and removal is not planned. Covered or partially covered stents are preferred when removal might be needed later, such as in benign strictures, or when the stricture location makes ingrowth especially likely. The choice often comes down to a case-by-case judgment about which failure mode is more tolerable for a given patient.

How Biliary Stents Are Placed

The most common placement method is endoscopic retrograde cholangiopancreatography, or ERCP. A flexible scope is passed through the mouth, down through the stomach, and into the duodenum, where the opening of the bile duct is accessed directly. A guidewire is threaded up through the blockage, and the stent is slid over the wire into position. ERCP is well-tolerated, does not require any incision, and has a relatively low complication rate.

When the blockage cannot be reached from below, percutaneous transhepatic biliary drainage (PTBD) offers an alternative. A radiologist inserts a needle through the skin and liver under imaging guidance, threads a wire down through the bile duct, and deploys the stent from above. A large national study found that the overall complication rate for endoscopic drainage was lower than for percutaneous drainage, with roughly 9% versus 12% experiencing a serious adverse event.⁹ Both routes are considered safe and effective, but endoscopic placement is generally attempted first when the anatomy allows it.¹⁰

A newer technique uses endoscopic ultrasound (EUS) to guide a needle from the stomach or duodenum directly into the bile duct, bypassing the normal papilla entirely. This approach has become an important fallback when standard ERCP fails, which happens in a meaningful minority of cases, particularly when tumor has distorted the anatomy. Pooled data from multiple studies show technical success around 92% and clinical success around 87%, though the complication rate is higher than standard ERCP, at roughly 18%.¹¹ For now, EUS-guided drainage is reserved for patients in whom conventional methods have failed or are not feasible.¹²

Why Stents Block and What Can Be Done About It

Every biliary stent will eventually fail if the patient lives long enough. The mechanisms differ between plastic and metal stents, but in both cases the duct environment is hostile to any foreign material. Bile is not sterile once a stent bridges the sphincter at the bottom of the duct, and bacteria ascend freely from the intestine.

In plastic stents, the primary failure mode is biofilm formation. Bacteria colonize the inner surface of the stent within days, secreting a sticky matrix that traps bile salts and calcium crystals. Enzymes produced by the bacteria break down bile components and generate deposits of calcium bilirubinate, calcium palmitate, and cholesterol that progressively narrow and eventually block the lumen.¹³ This process typically renders a plastic stent nonfunctional within three to four months, necessitating scheduled exchanges.¹⁴

Metal stents resist biofilm clogging because of their wider lumen, but they fail through different mechanisms. Tumor ingrowth through the mesh interstices is the dominant problem in uncovered designs. Covered stents trade ingrowth for sludge accumulation and migration. In rare cases, a stent can migrate far enough to cause damage elsewhere in the gastrointestinal tract, including perforation of the bowel wall.¹⁵

Stenting for Benign Strictures

Not all biliary stents go in because of cancer. Benign strictures, narrowings caused by inflammation, surgical scarring, or chronic pancreatitis, are a common reason for stent placement. The goal in benign disease is different: rather than keeping the duct permanently open, the stent gradually stretches the scar tissue over weeks to months so that the duct stays open after the stent is removed.

After liver transplantation, the surgical connection between the donor and recipient bile ducts can scar down, and stenting is one of the standard treatments. Plastic stents in this setting are typically exchanged every three to four months over the course of about a year, while metal stents can sometimes remain in place for three to six months before removal.¹⁶ The repeated exchange schedule is one of the main inconveniences for patients with benign strictures, and it is a key motivation behind research into biodegradable alternatives.

Bilateral Stenting for Tumors at the Hilum

When a tumor sits at the hilum, the junction where the right and left hepatic ducts merge, a single stent often cannot drain both sides of the liver. Two stents are needed, and they can be arranged in two ways. In the side-by-side approach, both stents sit next to each other within the common duct, each draining one side. In the stent-in-stent approach, one stent is threaded through the mesh of the other. Each technique has strengths that matter in different clinical moments.

A meta-analysis found that the stent-in-stent method had a higher technical success rate and fewer early complications, but the side-by-side arrangement resulted in longer stent patency and a lower rate of re-obstruction.¹⁷ A percutaneous study echoed this: side-by-side stents stayed patent for a median of 149 days compared with 75 days for stent-in-stent, and bilirubin dropped more quickly in the first week after placement.¹⁸ A more recent and larger pooled analysis, however, found the differences in re-obstruction narrower than earlier work suggested, with stent patency still slightly favoring side-by-side but overall survival comparable between the two approaches.¹⁹ In practice, the anatomy of the tumor and the angle of the ducts often dictate which configuration is feasible.

The Preoperative Drainage Controversy

For patients with pancreatic head cancer who are surgical candidates, it might seem logical to drain the jaundice first and operate on a healthier patient. The evidence, however, says otherwise. A landmark randomized trial found that patients who underwent preoperative biliary drainage with a plastic stent before surgery had a serious complication rate of 74%, compared with 39% for those who went straight to surgery. The drainage procedure itself accounted for much of the excess harm, with complications in nearly half the patients who were stented.²⁰

A meta-analysis of the broader literature confirmed that routine preoperative drainage increases overall postoperative complications and wound infections without improving mortality.²¹ The current consensus is that preoperative stenting should be reserved for specific situations: when surgery must be delayed (for example, to fit in a course of chemotherapy), when the patient has active cholangitis that needs urgent drainage, or when bilirubin is severely elevated and the surgical team judges that the liver needs time to recover before a major operation. Routine stenting of every jaundiced patient headed for surgery has fallen out of favor.

Quality-of-Life Effects of Biliary Stenting

For patients with incurable cancer, the question of whether a procedure improves how they feel matters as much as how long the stent stays open. Studies consistently show that biliary stenting relieves jaundice and itching rapidly and substantially. One prospective study reported that stenting produced complete relief of both jaundice and pruritus, along with measurable improvements in appetite, sleep, and overall quality of life.²²

Other work has nuanced this picture. In one trial of 40 patients, global health scores improved significantly within two weeks of stenting, along with reductions in pain and itching.²³ Another study, however, found that while itching improved dramatically at one month, overall quality of life actually declined slightly, reflecting the progression of the underlying cancer.²⁴ A separate prospective trial documented significant improvements in social function and mental health among patients whose bilirubin dropped after stent placement.²⁵ The takeaway is that stenting reliably fixes the symptoms caused by the obstruction itself, but it cannot reverse the decline caused by advanced cancer.

Emerging Stent Technologies

Much of the current research in biliary stenting aims to solve the fundamental problem of stent failure. Three directions stand out: drug-eluting coatings, antimicrobial surfaces, and biodegradable materials.

Drug-eluting stents borrow a concept from cardiology. The idea is to embed medication into the stent wall so it releases slowly into the surrounding tissue, suppressing tumor growth or biofilm formation. Early human data are limited, but preclinical work and small studies suggest these stents are safe and may slow obstruction.²⁶ Antimicrobial coatings using silver ions, chitosan, or embedded antibiotics target the bacterial biofilm that drives plastic stent clogging and contributes to metal stent sludge.²⁷

Biodegradable stents are perhaps the most intriguing development, especially for benign strictures where the stent is meant to be temporary anyway. Made from materials like polylactic acid, these stents dissolve on their own over weeks to months, eliminating the need for a second procedure to remove them. In a porcine model, a polylactic acid stent remained unobstructed for about 26 weeks before degrading.²⁸ A more advanced prototype incorporating the anti-inflammatory drug dexamethasone not only kept the duct open in a swine model for 12 weeks but actively reduced scarring; after 16 weeks the stent had dissolved completely and the stricture had healed without any need for removal.²⁹

In pediatric liver transplant recipients, biodegradable stents have already moved into clinical use. A series of 46 bile duct strictures treated with biodegradable stents in children showed a success rate above 90%, with only four patients ultimately needing surgical revision over a median follow-up of nearly four years.³⁰ For children, avoiding repeated sedation and endoscopy sessions is an especially meaningful benefit.

Imaging Stents After Placement

Once a stent is in place, doctors sometimes need to check whether it is still open without doing another endoscopy. MRI-based cholangiography can visualize the bile ducts noninvasively, but stent material matters for image quality. Plastic stents show up reasonably well on MRI because they do not distort the magnetic field, and the fluid column inside them can often be seen directly. Cobalt-alloy metal stents create heavy signal distortion that makes it impossible to assess whether the stent is open, though the stent’s position can usually be identified. Nitinol-based metal stents, the most commonly used type today, also interfere with imaging: in one study, stent position could not be reliably determined in any of the nitinol patients, and the internal diameter was visible in only one.³¹ In practice, this means that if a patient with a metal stent develops symptoms of re-obstruction, repeat endoscopy or a percutaneous cholangiogram is usually needed to confirm the diagnosis. CT scanning handles metal stents somewhat better than MRI for detecting gross complications, but direct visualization by scope remains the gold standard for assessing patency.

Anti-Reflux Designs and Other Mechanical Innovations

One contributor to metal stent failure is duodenal reflux: food, pancreatic juice, and intestinal bacteria wash backward into the stent, accelerating sludge buildup. Engineers have tried adding one-way valves to the distal end of the stent to block this reflux. A duckbill-type valve design showed promise in concept, but in clinical use the anti-reflux valve was found torn in over half of patients, suggesting the mechanical environment of the bile duct and duodenum is punishing for delicate valve structures.³² The idea remains appealing, but durable valve designs that survive the biliary environment are still a work in progress.