A large portion of the thousands of ERCP procedures performed the world over every day involve the placement of a stent in the bile ducts, the pancreatic ducts, or both. The clinical indications for stent placement can range from prevention of post-ERCP pancreatitis (PEP) to palliative decompression of the biliary system in cholangiocarcinoma patients. Depending on the clinical indication, the stent itself can be a permanent destination therapy to provide biliary decompression or a temporary therapy with multiple exchanges and up-sizing to help relieve the obstruction. Additionally, stents can be a very handy tool for a community gastroenterologist to
employ to help stabilize a patient, and act as a bridge while the patient awaits care with a senior therapeutic endoscopist at a tertiary referral center. Whatever the indication, the placement of a stent is, in general, a reliable, safe and easy modality. The ability to place a stent into the desired duct is a skill that every endoscopist who performs ERCP must master.
Stents are small, thin, tubular tools made of biocompatible plastic, metal, or a combination thereof. The first stent placed via ERCP to provide biliary drainage was reported in 1980. The stent in this particular case was a plastic single-pigtail stent fashioned out of an angiography catheter.1 Although technically successful at relieving the obstruction, the stent ultimately migrated into the biliary tree. Following this, double-pigtail stents were designed to prevent migration out of the biliary tree to the duodenum or proximally into the bile ducts. Further innovations resulted in the creation of side flaps to keep stents in proper position without having to resort to pigtails, which can be cumbersome to deploy and remove at a later date. Theoretically, all stents provide drainage and ductal decompression, whether they are in the bile duct or the pancreatic duct. A “good” stent is one that is easy to deploy, with minimal risk of malfunction, and that is resistant to clogging by bacterial biofilm, stone or sludge particles, or enteric contents.
This article will review the currently available biliary and pancreatic stents used in the context of ERCP, describing all types, subtypes, and permutations. We will also review the different roles for each of these stents and discuss the pros and cons of various stent designs. We will discuss stent deployment techniques, endoscopic requirements, and tools that help in stent placement. We will then share our experience with stent malfunctions and
tips on troubleshooting if needed. Finally, we will talk about adverse events, stent patency duration and the need for repeat procedures.
Plastic biliary stents
Currently, multiple types of plastic stents (PS) are available commercially for use in ERCP. They come in various sizes, lengths, diameters and are made of different biocompatible plastic materials such as polyurethane, polyethylene and polytetrafluorethylene (Teflon). Polyethylene stents are the most common in current clinical practice. A comprehensive list of commercially available plastic biliary stents is summarized in Table 1. The manufacturers make a myriad of shapes including straight stents, stents with a duodenal bend, or a center bend to accommodate for the intraduodenal portion of the CBD, and with combinations of flaps or double pigtails to prevent stent migration. Proximal flaps prevent distal migration, distal flaps prevent proximal migration (somewhat counterintuitively). The multiple combinations of length, diameter, shape and flap helps the endoscopist to make an appropriate choice of stent for the patient on the procedure table. Commonly used diameters include 7, 8.5 and 10 Fr stents (1 Fr = 0.33 mm) with lengths ranging between 5 and 15 cm. (Figure 1)
The underlying clinical indication determines the utility of plastic stents, as they are limited by their fixed-diameter and durability. The size of the working channel of the duodenoscope limits the maximum size of plastic stent to 12 Fr (4 mm), although in practice most plastic biliary stents in common use do not exceed 10 Fr. The majority of the plastic stents occlude in about 50% of patients in a period of 4 to 6 months. Self-expanding metal stents (SEMS) overcome some of these limitations. Although initially used as a permanent therapy for palliative purposes in patients with malignant biliary strictures, SEMS are now increasingly being used for benign indications as well.
Metal biliary stents
In the past, biliary self-expanding metal stents were made of stainless steel. Today, majority of the commercially available biliary SEMS are made of a nickel-titanium alloy known as nitinol. Nitinol became popular owing to its superior biocompatibility and ‘thermal memory’ properties. Nitinol stent was initially developed by the U.S. Navy. Its ‘thermal memory’ property allows the stent to be made at a certain diameter, cooled and compressed onto a delivery system. When deployed, the nitinol mesh tends to expand back to its original shape when exposed to body heat, thereby providing excellent dilation and durability in the treatment of biliary strictures.
Biliary SEMS are available as uncovered (UC-SEMS), partially covered (PC-SEMS) or fully covered (FC-SEMS) devices. (Figures 2 and 3) The covering membranes are made from various materials, the common ones being silicon, polyurethane or polytetrafluoroethylene. Table 2 summarizes the various commercially available uncovered biliary SEMS. Biliary SEMS have lengths ranging from 4 to 12 cm and diameters from 6 to 10 mm. The stents come mounted on a delivery system with diameters ranging from 5.0 to 10.5 Fr. A 0.035 diameter wire can usually be threaded into the system for placement into the biliary tree.
All SEMS are highly visible on fluoroscopy and additionally, the delivery systems have radiographic markers at both ends to enable visualization of placement before deployment. Individual stent types may be more visible than others. The outer sheath of the system is transparent allowing for visualization of the distal end of the stent during release as a means of reducing the risk of mis-deployment. Some stents can be recaptured until 80% of their deployment has been achieved but others cannot be re-constrained at all i.e. Viabil stents. Some commercial brands have a ‘point of no return’ marker on the stent delivery system, beyond which re-constrainment can no longer be achieved. Some, but not all, PC-SEMS and FC-SEMS have flanges at the ends to prevent migration. Additionally, to aid removal these devices can have a string or a lasso or even a prominent metal strut at one of the ends, which can be pulled with any grasping forceps to collapse the stent and allow it to be removed in one piece. Table 3 and Table 4 summarize the commercially available PC-SEMS and FC-SEMS, respectively.
Mechanical properties of biliary metal stents
The mechanical properties of a metal stent are defined by the stent design, type of metal used, covering materials and the braid pattern. Clinical outcomes are primarily affected by the radial and axial forces exerted by the SEMS that result from a combination of these factors. The radial force determines the patency of the stent by counteracting the inward force of a stricture. The immediate expansion of a SEMS is usually partial after deployment. With time, usually a few days after deployment, the ‘shape memory’ of the metal alloy gradually expands the SEMS to its full capacity. In some SEMS, the axial force maintains conformability of the stent to the duct in which it is placed.
FC-SEMS can be further classified into laser-cut and braided SEMS. Braided SEMS are also sometimes referred to as woven. Laser-cut FC-SEMS have larger cells and mesh as compared to the braided type and demonstrate minimal to no stent foreshortening due to lower axial forces. These features, by and large, enable accurate placement in the desired location.
SEMS made out of biodegradable materials and FC-SEMS with chemotherapy drug eluting properties have long been being investigated for use in malignant biliary strictures, but have yet to come to market.2 Data for biodegradable biliary stents is limited at this time. In a single center retrospective analysis of adult patients who underwent percutaneous placement of biodegradable biliary stents for post-liver transplant biliary strictures, the patency rate was 80% (n = 12/15) at 12-months follow-up.3 A large, multicenter, prospective study from Spain demonstrated stent patency rates of 78.9% at 60-months follow up with percutaneous placement of biodegradable biliary stents for benign strictures. Only 12% (n = 18/40) needed a second stent placement.4
SEMS with drug-eluting properties are not available for commercial use at this time. In drug-eluting stents, the stent covering is impregnated with therapeutic agents such as 5-fluorouracil, paclitaxil and gemcitabine with the goal of chemotherapy drug delivery at the tumor site. Theoretically, the idea underpinning a drug-eluting biliary stent is to prevent tumor in-growth in addition to local cancer treatment, but in practice this has been difficult to demonstrate. A meta-analysis of limited data demonstrated no added benefit of a drug eluting biliary metal stent as compared to covered SEMS.5 Biliary stents complexed with chemicals such as sodium cholate and EDTA (ethylenediaminetetraacetic acid) have been found to help dissolve biliary stones, but these are not commercially available.6
Common clinical situations where a stent is indicated in an ERCP procedure are as follows:
benign and malignant bile duct strictures, chronic pancreatitis related bile duct strictures, post liver transplantation or surgery related post anastomotic strictures, bile leaks, bile duct stones with incomplete clearance or large duct stones that need endoscopic electro-hydraulic lithotripsy, post-sphincterotomy bleeding, and primary sclerosing cholangitis, among others. Common causes of malignant biliary obstruction include cholangiocarcinoma, pancreatic adenocarcinoma, ampullary carcinoma, metastatic disease to the liver, lymphadenopathy of porta hepatis nodes or metastatic disease.
The clinical indication, cholangiogram findings and overall disease prognosis can help guide the endoscopist’s decision regarding a temporary or permanent stent requirement. Based on that, the decision for plastic or metal stents can be made. Theoretically, either a plastic stent or a metal stent can be used for palliation in patients with malignant biliary obstruction. A larger size plastic stent (10 Fr or above) provides better patency than smaller size (7 Fr or lower) for obvious reasons. A metal stent, on the other hand, is designed with a larger diameter with goals to achieve a longer duration of patency as compared to plastic stents, and can reduce the rate of re-interventions. In a large meta-analysis, SEMS and PS were comparable in the palliation of malignant biliary strictures; however, SEMS demonstrated longer stent patency, lower complications and fewer re-interventions.7
An uncovered SEMS is almost always used in the therapy of patients with malignant biliary strictures with the goal of palliation. UC-SEMS are associated with a lower rate of migration compared to a FC-SEMS. UC-SEMS are subject to tumor ingrowth and are, for all intents and purposes, permanent and not removable. (Figure 4 and Figure 5) Nevertheless, an UC-SEMS would be the ideal choice in situations where stenting is required across side branches, the cystic duct orifice in patients with an intact gallbladder, or in patients with cholangiocarcinoma in order to avoid blockage of the ducts being traversed. (Figure 6)
FC-SEMS on the other hand, have demonstrated longer patency as compared to UC-SEMS. However, sludge formation and stent migration can occur with these devices. Newer FC-SEMS with anti-migration systems have been developed to limit stent migration events. The Hanaro M.I Tech stent has ‘anchoring flaps’ in the proximal end, flared ends to prevent migration; and comes with one proximal and one distal end lasso for easy retrieval. The Viabil stent system from Gore & Associates, Inc., has fully covered ‘anchoring fins’ that reduce the rate of migration and this device has a non-foreshortening design to enable precise stent placement.
As mentioned earlier, FC-SEMS can be further classified into laser-cut and braided stents. Laser-cut FC-SEMS have larger cells and mesh as compared to the braided type and demonstrate minimal to no stent shortening due to lower axial force. These features promote easy and accurate placement in the desired location. However, laser-cut stents are generally uncovered and are difficult to remove in patients with recurrent malignant biliary obstruction. Data is limited as to the comparative efficacy of laser-cut FC-SEMS to braided FC-SEMS. In a retrospective study from Japan that assessed 47 patients (24 laser-cut stents and 23 braided), braided FC-SEMS demonstrated a longer time to recurrent biliary obstruction as compared to laser-cut FC-SEMS. Stent migration rates were comparable between the two.8
Choosing a stent length
The choice of length of the stent to be deployed is based on the assessment of the length of the stricture as seen on cholangiogram. Very often this assessment is based on the endoscopist’s experience. Ideal positioning of the stent should allow for drainage of bile from a location above the proximal end of a stricture. This can be achieved by positioning the stent at least 1-2 cm above the upper edge of the stricture as visualized on the fluoroscopy image and the intestinal end should extend at least 1cm into the duodenum. A given stent length usually reflects the entire length of the stent, however in some stent types this length might represent the portion between the flaps. The endoscopist should always check the information on the cover of the stent package before opening it to ensure proper understanding of the device being selected.
Assessing the length of a stricture can be carried out in multiple ways. The endoscopist can use the initial cannulating catheter to gauge the length by measuring the distance from the top end of the stricture on the fluoroscopy image to just when the catheter tip is out of the papilla on the endoscopic view. During the entire process of the withdrawal, the endoscopist holds the cannulating catheter outside the biopsy port to measure the length or mark the cannulating catheter at the biopsy port before initiating the withdrawal. The radiograph length on the fluoroscopy can be used as well to assess the length, with the duodenoscope providing a ruler in each image. Some catheters have fluoroscopic markers to aid in the measurement of the length of a stricture. Dilation balloon catheters have radio-opaque markers which can be used to measure the length as well. In practice, many experienced endoscopists can “eyeball” the stenosis length with great accuracy without the aid of devices to measure it precisely.
Delivery system and accessories
A variety of stent delivery systems make the deployment process possible. Plastic stents <8.5 Fr can be placed directly over a guidewire and pushed into position using a pusher tube or with a sphincterotome, a balloon catheter, or other wire-guided devices. A key aspect in this technique is to be careful not to inadvertently push the stent fully into the bile duct, as pulling it back out into position would then require an additional modality such as using a ‘raptor’ or ‘rat-tooth’ forceps and can consume significant time. Using a guidewire helps provide rigidity to the stent and keeps it stable when being advanced across the stricture or above a stone. Once the stricture margins are defined by contrast injection following deep cannulation and wire insertion, the guidewire must be placed well proximal to the stricture into the bile ducts. More than one guidewire might be necessary based on the duct systems to be drained to achieve resolution of cholestasis.
All standard duodenoscopes have a 4.2 mm working channel that can accommodate stents up to 11.5 Fr. A 3.7 mm operative channel can accommodate a PS up to 10 Fr. Usually, an 8.5 Fr stent can be placed without the need for sphincterotomy or stricture dilation. A 10 Fr stent may require sphincterotomy and/or stricture dilation. However, placing more than one stent would, in general, require sphincterotomy depending on the size of the native papilla. Similarly, dilation of the stricture might be needed to accommodate the stents being placed. When needed, stricture dilation can be achieved by various tools, such as a biliary dilation balloon or a Soehendra biliary dilation catheter. Rarely, a Soehendra stent retriever or a RFA (radiofrequency ablation) catheter can be used to open ‘dilation-resistant’ strictures.
Stent placement Plastic stent placement
Based on the stent delivery systems, either the inner guiding catheter alone or with the stent is advanced over the guidewire. Minimal resistance and easy passage should always be felt, and unwanted excessive pressure should be avoided while passing any stent system. The elevator must remain closed when advancing the stent system into the working channel. When the stent impacts the elevator, it is gently opened to reveal the tip of the stent system, and the stent and any delivery system is advanced over the guidewire into the papilla. A short endoscopic position is often helpful in maintaining a stable position.
The stent is often advanced into position by repeated small ‘open close’ movements of the elevator with gentle stable push from the endoscopist. This is also sometimes referred to as “walking the stent up the duct.” This ensures small step-by-step advancement of the stent into the biliary duct. Once an optimal positioning is ascertained on the radiograph image, the inner guiding catheter and/or guidewire is then removed while the endoscopist maintains forward pressure for the stent to deploy in the right position. A post-placement radiograph image should be checked to ensure contrast medium drains through the stent and that image is often saved for documentation purposes. The final placement of a pigtail plastic stent differs slightly in that the duodenoscope has to be partially withdrawn to endoscopically visualize and make room for the intestinal pigtail segment to allow it to open up and curl into proper position.
When placing multiple stents, it could be a useful strategy to place a slightly longer stent first to reduce the risk of proximal migration due to friction alongside the walls from the subsequent stent. Use of a sterile lubricant such as silicon spray can sometimes help reduce friction, but in practice is rarely needed.
Metal stent placement
The majority of the steps involved in metal biliary stent placement are similar to those used during the plastic stent deployment. In most cases, the release of a SEMS is performed under endoscopic and fluoroscopic guidance. Unlike a PS, the SEMS is constrained on the delivery system catheter by an outer plastic sheath or a string release mechanism. After the stent, constrained onto the delivery system, is advanced into the bile duct and the correct position is finalized over a guidewire, the outer sheath is gradually and carefully withdrawn. During the deployment process, the stent should be maintained at the correct position by maintaining a back-tension on the device, as it tends to move away from the endoscope and proximally into the duct if left unattended. If such proximal displacement occurs, the majority of SEMS can be recaptured as long as the deployment is up to 80% complete. Successful deployment of a biliary SEMS requires prior knowledge of the stent system, its foreshortening properties, and a good communication between the endoscopist and the technician to adjust and avoid mis-deployment before the stent can be recaptured.
A final cholangiogram picture should be captured to check, confirm and document stent placement. Endoscopic and fluoroscopic images showing the passage of bile and contrast, respectively, can be used to confirm successful biliary drainage. If the SEMS has been deployed in an excessively proximal position, it can be pulled into position immediately after deployment with a snare or a rat-tooth grasping device and adjusted distally, even if it is an uncovered SEMS. In cases where the SEMS is deployed too distally, often hanging low into the lumen of the duodenum, the stent can either be removed and replaced with a new stent or, rarely, the excess luminal portion of the stent can be cut using argon plasma coagulation. In practice it is easier to adjust a SEMS into a more distal position than into a more proximal one. Excessive stent length in the duodenum can result in ulceration, bleeding and, rarely, perforation of the contralateral duodenal wall.
Suprapapillary placement of a biliary SEMS is often warranted in patients with malignant proximal biliary strictures, involving the hepatic hilum or locations above. In these patients, the length of the SEMS might not be adequate to traverse the ampulla. Indeed, if the stricture is very proximal, there is often no reason to bridge the entire stent down to the duodenum. In these patients, the stent can be placed fully within the biliary tree. Such stents are referred to as “fully internalized” or “all internal” stents. In patients who have not undergone prior biliary sphincterotomy, fully internalized stents provide a theoretical advantage of preventing duodenal content reflux into the bile duct. In general, fully internalized stents can be accessed from below via ERCP on subsequent procedures, if required.
Knowledge about drainage holes on any given stent is paramount to achieve the best and sustained results of biliary decompression. The location of end holes and side holes must be taken into account. The drainage hole distribution is different in a straight PS with end flaps as compared to double pigtail plastic stent. Stents bearing the same brand name can differ based on the presence or absence of side drainage holes, such as the Viabil FC-SEMS. Challenging situations can arise when obstructions extend into multiple side branches of the bile ducts (as in Bismuth type 4 cholangiocarcinoma). More than one plastic stent might be needed in such situations to achieve adequate palliation.
Distal biliary drainage
Distal biliary obstructions are one of the most straightforward clinical indications for stent placement. In situations of short, benign distal biliary strictures such as seen in chronic pancreatitis patients, post-sphincterotomy ampullary strictures or idiopathic cases, a 8.5-10 Fr, 5 cm PS would usually be ideal. Sometimes, multiple stents can be placed alongside to help dilate the ampulla. Data supports the placement of more than one wide bore PS, side-by-side, to achieve best clinical outcomes as compared to one 10 Fr PS. This strategy demonstrated excellent effectiveness (80% to 90%) in the treatment of postoperative biliary strictures.9 In modern practice, the idea of placing multiple PS in a side-by-side manner has mostly given way to the placement of a single FC-SEMS for ease of placement and simplicity. In cases of irretrievable bile duct stones, plastic pigtail stents are usually better suited than straight plastic stents for maintaining drainage over the long term. An important limitation when PS are used is the need to undergo multiple ERCP procedures for stent exchange. In vitro studies exist that have analyzed stents that elute chemicals like sodium cholate and EDTA with goals of dissolving biliary stones.2
These stents are still experimental and are not commercially available.
The placement of a FC-SEMS instead of multiple PS can reduce the number of repeat ERCPs needed for stent exchange. A meta-analysis of eight RCTs comparing covered SEMS to multiple PS in benign biliary strictures, demonstrated comparable stricture resolution rate (risk ratio = 1.02, 0.96- 1.1) and stricture recurrence rate (risk ratio = 1.68, 0.72-3.88). However, the mean number of ERCPs was significantly lower with covered SEMS.10 The FC-SEMS were left in-situ for 10-12 months in chronic pancreatitis patients and 4 to 6 months in post liver-transplant patients.10 The Wallflex RMV stent by Boston Scientific is approved by US FDA for an indwell time of 12-months in the treatment of biliary strictures secondary to chronic pancreatitis.
Although SEMS are more expensive than PS, the overall lesser number of repeat ERCP procedures with SEMS as compared to PS seems to offset the overall cost. Covered SEMS are avoided by some endoscopists if the gallbladder is still present to avoid potential cystic duct occlusion and the risk of cholecystitis. If unavoidable, a small plastic stent can be placed inside the cystic duct prior to placing a FC-SEMS in the CBD, but in practice this is rarely performed. Similarly, acute pancreatitis secondary to pancreatic duct obstruction is also reported when FC-SEMS are used. Nonetheless, FC-SEMS are widely used in patients with and without an intact gallbladder in current clinical practice.
Data thus far have demonstrated comparable clinical outcomes in terms of technical and therapeutic success rates, mortality and overall adverse events between SEMS and PS in patients with malignant biliary obstruction.7 A meta-analysis of twelve studies reported superior performance of covered SEMS as compared to UC-SEMS in prevention of recurrent biliary obstruction in patients with malignant distal biliary obstruction. The pooled mean difference was 45.51 days (11.79-79.24) longer with a covered SEMS. However, rates of stent migration, sludge formation and tissue overgrowth were higher with covered SEMS and tissue ingrowth was noted more frequently in patients receiving UC-SEMS.11 Data comparing PC-SEMS and FC-SEMS are limited. PC-SEMS might have better clinical performance in terms of time to recurrent biliary obstruction secondary to malignancy. In a retrospective study of 101 patients who received SEMS for unresectable malignant distal biliary obstruction (44 UC-SEMS, 28 PC-SEMS, 29 FC-SEMS), no survival differences were noted, however median time to recurrent biliary obstruction was 199 days, 444 days & 194 days respectively with UC-SEMS, PC-SEMS and FC-SEMS.12
Proximal biliary obstruction
Patients presenting with cholestasis secondary to hilar or more proximal biliary obstruction can present interesting challenges for successful stent placement. Cross-sectional imaging with CT or MRI is generally obtained and reviewed prior to planning the procedure to ascertain the anatomy and plan the modality of stent placement.
Many patients with proximal biliary obstruction warrant consideration of bilateral stent placement. Biliary drainage in these patients is technically challenging even for experienced endoscopists, as there is often very little room for stents to fit at a hilum already crowded via tumor. Bilateral drainage can be achieved by either a ‘side-by-side’ stent insertion or a ‘stent-in-stent’ technique. To achieve this, two or more guidewires are placed inside the biliary systems to be drained, followed by placement of equal sized or one big and one small caliber plastic stents depending on the intra-procedure situation.
SEMS can also be used to treat hilar obstruction, usually in patients with unresectable disease. Bilateral SEMS placement is also technically challenging and complicated by the self-expanding nature of these devices. I.e., the first stent may take up more than its “share” of the room at the hilum, and the placement of the second SEMS is often more difficult than the first. In the ‘stent-in-stent’ technique, a balloon dilation is performed through the meshes of the first stent followed by placement of the second stent through the widened mesh, if needed. Some SEMS come designed with large diameter mesh cells to facilitate deployment of the second SEMS. Niti-S (Taewoong Medical, South Korea) and Flexxus (ConMed, California, USA) have large mesh areas to allow passage of a second SEMS. Additionally, smaller stent delivery introducers like the 6 Fr introducer, Zilver 635 (Cook Medical, Bloomington, Indiana, USA); can come very handy.
Post-procedure cholangitis is a risk if both lobes of the liver are opacified with contrast and liver segments are not fully drained via stent placement. Contrast injection is often kept to a minimum to avoid bacterial seeding into the obstructed/non-draining portions of the intrahepatic ducts. Drainage of both lobes of the liver is usually recommended. However, in a multicenter, international retrospective study, bilateral stent placement was associated with higher risk of death and adverse events in the treatment of cholangiocarcinoma.13 Therefore, the issue is not decided. Selective drainage of specific liver areas can be planned and performed based on preprocedural review of MRCP images. Sometimes, additional percutaneous biliary drainage might be needed to achieve adequate decompression of the obstructed areas.
Preoperative stent placement
In preoperative patients, a Monte Carlo decision analysis study and a meta-analysis of five studies that compared SEMS to PS, concluded that in patients with resectable distal pancreaticobiliary cancer, the placement of a short-length UC-SEMS provided equal or superior efficacy and reduced overall cost as compared to PS placement. An infra-hilar placement of a 4 to 6 cm SEMS should be considered on a patient-by-patient basis before anticipated resection.14,15 In clinical practice, this approach is widely used.
Post-ERCP pancreatitis is more often related to the ERCP procedure per se than to the stent itself. Data seems to suggest that sphincterotomy is not protective against post-ERCP pancreatitis before placing a stent in patients with distal biliary obstruction. On the contrary, in patients with biliary leak, sphincterotomy demonstrated risk reduction in prevention of post-ERCP pancreatitis.16 Immediate adverse events related to stent placement include device related issues, including failure to deploy and malpositioning. Failure to adequately lubricate the delivery device channels can, on rare occasions, cause arrested withdrawal of the outer sheath resulting in deployment failure and/or a misplaced stent.
Other adverse events related to stent placement can include cholangitis, hemobilia and bile duct or luminal perforation. Ineffective drainage of segments opacified during cholangiogram can lead to cholangitis. Persistent cholangitis despite antibiotics can warrant a repeat procedure. Stent placement in a patient with a friable tumor can cause hemobilia. Retrieval of blood clot might sometimes be necessary if causing clinically significant cholestasis. However, the majority of hemobilia usually self resolves without causing any clinically significant issues. A malpositioned stent can cause ulceration, perforation and bleeding of the contralateral duodenal wall.
Commonly reported stent-related late adverse events are migration and occlusion. Tumor ingrowth, biliary sludge, biofilm formation, cell hyperplasia and food-bezoar are common causes for stent occlusion. Migration is more common with FC-SEMS and cholecystitis can occur with FC-SEMS in patients with intact gallbladder as previously mentioned.
Pancreatic duct stents
Pancreatic duct (PD) stents are usually plastic stents of small caliber. Usually, 3 to 7 Fr in terms of size. The stent diameter size is chosen based on the clinical indication. 3 to 5 Fr are usually used for prevention of post-ERCP pancreatitis in high-risk patients, with 5 Fr being the most commonly employed. The goal is for the stent to aid in pancreatic fluid drainage and provide pancreatic duct decompression. A 5 Fr x 5 cm unflanged pancreatic duct stent is usually ideal to prevent post-ERCP pancreatitis, but individual opinions on stents vary and many options are available. Various commercially available pancreatic duct stents are summarized in Table 5. Pancreatic stents are available as straight stents, single pigtails, double pigtails, and with or without internal and/ or external flaps.
In addition to end drainage holes, all pancreatic duct stents come with multiple side holes to aid drainage of secretions via pancreatic side-branches. Stents with anti-migration side flaps are used when spontaneous stent passage is undesirable such as in patients with chronic pancreatitis induced PD strictures, pancreatic duct stones, etc. A stent without internal flaps is popular for prophylaxis of post-ERCP pancreatitis as it can spontaneously pass in a few days after placement, while others prefer stents with internal flaps that need to be retrieved at a later date to ensure that the stent does not migrate, which may produce a superior effect when reducing post-ERCP pancreatitis rates. (Figure 7)
Placement of a pancreatic duct stent involves a guidewire into the pancreatic duct to a point deep enough that the wire is stable. This is usually performed when the site of pathology is identified on pancreatogram, i.e., a stricture. The pancreatic duct stents are passed over the guidewire, generally without an inner guiding catheter/delivery system as they are often not needed. A pusher tube or similar device such as standard catheter, balloon catheter or the sphincterotome can be used to push most pancreatic stents into position. Dilation of the lesion can be performed if necessary prior to stent placement. With the pusher catheter in position, the guidewire is removed, and the stent is left in place after the pusher catheter is withdrawn.
The Taewoong Medical, Bumpy – Niti – S stent is a SEMS designed for drainage of the main pancreatic duct. It has an atypical mesh design with irregular cell sizes that exert different radial forces in different sections of the stent. Owing to this property, the stent does not completely compress and occlude the PD side branches. Other FC-SEMS can be used off-label with good results; however, the size, length and drainage holes should be considered for effective clinical outcomes. To enable smooth placement, pre-dilation of the PD stricture is sometimes helpful, which can be usually achieved with a small sized balloon such as the Hurricane 4 mm by 4 mm balloon.
Placing a short, small caliber pancreatic duct stent can be risky for inadvertent deep placement. An inward migrated pancreatic duct stent can be very difficult to retrieve. Maneuvers to try and retrieve the stent can result in further distal displacement into a side branch or to the pancreatic tail. A single pigtail stent with the pigtail in the duodenum is available in such situations and in situations where deep pancreatic duct drainage is warranted such as in cases with pancreatic leak in the distal body or tail of the pancreas, or a disconnected duct, although even stents with external pigtails can migrate proximally. Proximally migrated pancreatic duct stents can be difficult to remove and often require significant interventions.
The 1980s witnessed the introduction of SEMS for the treatment of biliary obstruction in the context of ERCP. Bare metal SEMS paved the way for partially covered and fully covered metal stents with various biocompatible polymer coatings to prevent tissue ingrowth. Multiple sizes and shapes of SEMS are being investigated with goals of easy delivery, reduced rates of migration and enhanced durability.
Biodegradable biliary stents and drug eluting biliary stents might gather increasing attention over the next many years. A fully biodegradable helical structured biliary stent ARCHIMEDES developed by Q3 Medical Devices Ltd., has obtained CE certification in 2018. Studies have evaluated the clinical outcomes of PDX biliary stent made by ELLA-CS, Hradec Kralove, Czech Republic. Effectiveness and safety have been demonstrated in the treatment of benign biliary strictures secondary to liver transplantation.2 These biliary stents have been designed with three rates of degradation (fast, medium, and slow) to meet patients’ needs based on the clinical condition being treated.
Research is underway on inventing the best possible biodegradable polymer that can withstand as well as be compatible with pancreatico-biliary enzymes. Biodegradable magnesium alloys have been considered potential options after their excellent performance in the cardiovascular field. UNITY-B developed by Q3 Medical Devices Ltd., is one such magnesium based biodegradable stent developed for use in biliary strictures that has obtained CE certification.
As with drug eluting SEMS, drug eluting biodegradable biliary stent is another area of exciting research. Multiple chemotherapeutic drugs are being investigated with various biodegradable polymers. Studies at this time are limited to in-vitro porcine models. Innovative stents designed using 3-Dprinting technology and made by tissue engineering approach, with goals of customizing it to individual patient anatomy, sounds more exciting than ever.2
In conclusion, placement of a biliary and/or pancreatic stent is an integral skill to know and master in ERCP procedures. Multiple stent types exist with a myriad of shapes, sizes, lengths, anti-migration flaps, and drainage holes for the endoscopist to choose from. The choice of stent should be based on the clinical indication, underlying pathology, cholangiogram findings and anticipation of repeat procedures. Although the stent systems are manufactured with easy-to-use standard mechanisms, subtle nuances in the deployment process of certain stents must be taken into account, and measures should be taken to avoid deployment complications.
- Soehendra N, Reynders-Frederix V. Palliative bile duct drainage-a new endoscopic method of introducing a transpapillary drain. Endoscopy 1980;12:8-11.
- Song G, Zhao HQ, Liu Q, et al. A review on biodegradable biliary stents: materials and future trends. Bioactive Materials 2022;17:488-495.
- Abulqasim S, Arabi M, Almasar K, et al. Percutaneous Transhepatic Biodegradable Biliary Stent Placement for Benign Biliary Strictures. Digestive Disease Interventions 2021;5:307-310.
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Babu P. Mohan MD1 Douglas G. Adler MD2
1Orlando Gastroenterology PA, Orlando, FL
2Gastroenterology, Center for Advanced Therapeutic
Endoscopy, Centura Health, Denver, CO