Pancreaticobiliary Stent Retrieval

Plastic Biliary Stents (see Chapter 22 )

First reported to be used in 1980, endoscopically placed plastic biliary stents (PBS) provided a safe and cost-effective alternative to percutaneous and surgical biliary interventions for relief of malignant biliary obstuction. Removal of PBS is usually performed with ease if performed within months of placement. On the other hand, extraction of PBS is hindered when proximal or distal migration occurs. Risk factors associated with stent migration include the presence of common bile duct dilation, choledocholithiasis, and benign biliary strictures. Proximal strictures and the use of long biliary stents are associated with distal migration, whereas distal strictures and the use of short biliary stents are associated with proximal migration. Factors that make proximal migrated stent retrieval more challenging include:

• Migration upstream from a stenotic region

• Migration into the peripheral branches of the intrahepatic biliary system

• Inconsistency between the biliary stent and its axis in patients without biliary dilatation

• Stent impaction into the bile duct wall

Stents are nearly always removable when accessible. Proximally migrated stents are more difficult to retrieve, but the success rate of endoscopic removal ranges from 70% to 100%. If endoscopic retrieval is unsuccessful, a second stent can be placed while leaving the first stent in place to facilitate drainage and allow access with subsequent reattempt at retrieval. Distally migrated stents generally pass through the intestine without complication; however, cases of perforation and obstruction requiring surgical intervention and even death have been reported.

Self-Expandable Metal Stents

To overcome issues with small-caliber plastic stents, larger-diameter SEMS were designed to provide prolonged patency. At present, SEMS are favored for malignant palliation (see Chapter 39 ) and cSEMS have an increasing role in the management of benign conditions, including benign strictures, complex bile leaks, biliary perforation, and postsphincterotomy bleeding (see Chapter 8, Chapter 43, Chapter 44 ).

Established and potential risk factors for difficult SEMS extraction include:

• Type of SEMS. Data support a favorable retrieval rate for cSEMS at approximately 78% to 99%. Instances of unsuccessful cSEMS extraction have been attributed to tissue overgrowth and impaction against the bile duct wall. By design, uncovered SEMS (uSEMS) have limited removability because of tissue embedding and ingrowth, and most endoscopists limit their use to palliation. As expected, the reported successful removal rate of uSEMS is poor, ranging between 0% and 38%. In a 5-year retrospective review, cSEMS were removed more successfully than uSEMS (24/26 [92.3%] vs 5/13 [38.4%], respectively [ p < 0.05]).

• Stent dwell time. In a study evaluating the efficacy of endoscopic SEMS retrieval, 14/19 patients underwent successful stent extraction. The mean dwell time for those with successfully removed SEMS was shorter than for those with nonremovable SEMS (94.9 ± 71.5 days vs 166.2 ± 76.2 days, p = 0.08), though this was not statistically significant.

• Stent-specific structural properties. Familiari et al. hypothesized that an interlaced rather than zigzag mesh design may contribute to more successful stent extraction because of its greater ability to endure longitudinal traction during retrieval. Yet multivariate analysis did not demonstrate a significant correlation (interlaced mesh vs zigzag mesh, p = 0.258). Similarly, Ishii et al. correlated differences in the rate of shrinkage and straightening during attempted retrieval with the stent’s structural ability to transmit force and ultimately to ease extraction. The authors described that removal of Niti-S Biliary ComVi stents (Taewoong Company, Seoul, South Korea) was slightly more difficult than Wallstents (Boston Scientific, Tokyo, Japan); however, the study was limited by the small number of patients.

Indications and Contraindications

The indication for biliary stent retrieval depends on the nature of disease for which the stent was placed (benign or malignant) and the patient's life expectancy. At present, PBS and cSEMS are used for benign indications, whereas PBS, cSEMS, and uSEMS are used to alleviate malignant obstruction. In benign disease, both PBS and cSEMS must be removed because of the risk of occlusion and cholangitis. The indications to remove PBS and cSEMS are the same and include:

• 1.

  Resolution of underlying biliary disease. Once the beneficial effect of the stent has been achieved, it should be removed. The timing may vary depending on the nature of the underlying disease. For instance, the outcome after stent placement for chronic pancreatitis-related benign biliary strictures is improved with prolonged stent placement, whereas shorter durations of stent placement are necessary for complicated choledocholithiasis and bile leaks. Some studies suggest that resolution of disease is the most common indication for stent removal, whereas others identify stent-related malfunction (described next), including occlusion, as the leading indication for retrieval.

• 2.

  Stent malfunction. There are two main causes of biliary stent malfunction. The first is stent occlusion via sludge, debris, duodenal reflux, tissue hyperplasia, or tumor ingrowth and overgrowth. The second is stent migration, either proximally into the biliary tree or distally into the intestine.

  Occlusion of a biliary stent results in obstruction of the biliary tree that can manifest with mixed-type liver injury, jaundice, pruritus, or cholangitis. Sludge formation appears to play a predominant role in the occlusion process. Evaluation of explanted, occluded stents with electron microscopy and biochemical analysis reveals bacteria and/or fungi, microbial byproducts, bilirubin, insoluble dietary residue, proteins, and cholesterol crystals without overt cholesterol or pigment calculi. Upon stent insertion, the inner surface is rapidly covered by host proteins that enhance bacterial adherence and subsequent biofilm formation. The biofilm permits bacteria to adhere firmly to the stent, and thus continuous deposition of microbial degradation products and growth of colonies can eventually lead to narrowing of the stent lumen. According to Poiseuille's law, as the narrowed lumen slows bile flow, spontaneous and microbial-driven precipitation of bile salts increases bile viscosity and ultimately leads to complete stent occlusion. PBS occlusion with need for reintervention is as high as 40% and appears directly related to stent dwell time. Treatment of PBS occlusion entails retrieval of the occluded stent followed by replacement (if needed), with the number and type of stent(s) dependent on the underlying indication.

  With respect to SEMS, hyperplastic tissue and tumor ingrowth are more commonly associated with uSEMS occlusion, whereas tumor overgrowth (i.e., occlusion of the stent ends) and sludge formation are associated with occlusion of cSEMS. Sludge and refluxed duodenal contents can cause occlusion of both types of SEMS, though the risk may be higher in those with cSEMS. Mechanical clearance of the occluded stent with an extraction balloon is one method to address the malfunctioning SEMS and is associated with a high reocclusion rate and short patency. Alternatively, a PBS or SEMS can be placed within an occluded SEMS, with supportive data demonstrating prolonged patency relative to mechanical clearance. Data comparing the relative efficacy of PBS versus SEMS for use in stent-in-stent (SIS) SEMS occlusion are limited. In a systematic review of 10 retrospective studies, the risk of reocclusion, patency duration, and overall survival were not significantly different between patients who received PBS versus SEMS for occluded SEMS; however, there was considerable heterogeneity between studies. Because of the lack of significant difference in performance, some have concluded that PBS placement may be the more cost-effective intervention, though data on the subject are limited. Some authors support removal of the occluded stent and deployment of a new SEMS.

  Migration is the other main cause of biliary stent malfunction. Complete external migration usually causes recurrence of symptoms such as abdominal pain, jaundice, or cholangitis, but it may be asymptomatic if the underlying disease process has resolved (i.e., stricture resolution). In those with ongoing or recurrent symptoms, reassessment of the need for repeat stent insertion must be pursued. Externally migrated stents generally pass uneventfully through the intestine, and therefore endoscopic removal is not necessary. Infrequently, migrated stents can cause adverse events that result in the need surgery or even death. Stents that migrate distally but remain partially in the common bile duct may embed in the contralateral duodenal wall. In such cases, apart from signs of stent occlusion, mucosal injury, including bleeding and perforation, can occur. Most reported instances of proximal stent migration manifest with clinical symptoms and can be difficult to manage. The reported success rate of removal of proximally migrated stents is favorable and ranges from 70% to 100%.

• 3.

  Stent-related adverse events. Clinical symptoms related to stent insertion can be considered an indication for stent removal. Acute cholecystitis from cystic duct obstruction has been reported as a specific adverse event of cSEMS placement, with a variable incidence ranging from 0% to 10%. The risk is believed to be less when cSEMS are placed distal to the cystic duct takeoff and when uSEMS are used. Acute pancreatitis has been associated with large-caliber PBS and SEMS placement, with an incidence ranging from 0% to 9%, though most studies did not control for known contributors to PEP. The predisposing injury is thought to be related to direct or indirect occlusion of the pancreatic orifice. In a recent large retrospective review of 544 patients undergoing stent placement for malignant obstruction, the risk of pancreatitis was significantly higher in those receiving SEMS (7.3%) versus PBS (1.3%) and the frequency did not significantly differ for cSEMS (6.9%) versus uSEMS (7.5%). Most recommend a biliary sphincterotomy before placement of biliary stents because of the potential for reducing PEP, though the data supporting this are conflicting. A recent meta-analysis of three randomized controlled trials revealed a reduced incidence of PEP (odds ratio [OR] 0.34, 95% confidence interval [CI] 0.12 to 0.93, p = 0.04) but an increased incidence of post–ERCP-related bleeding with biliary sphincterotomy (OR 9.70, 95% CI 1.21 to 77.75, p = 0.03). Abdominal pain is rarely reported after placement of biliary stents. In a prospective study evaluating the efficacy of cSEMS in benign biliary strictures, abdominal pain necessitating stent removal was seen in 2/79 patients (2.5%).

Absolute contraindications for stent removal are limited to circumstances when ERCP is also contraindicated. For instance, the development of duodenal stenosis after placement of a biliary stent in patients with benign or malignant biliary occlusion may therefore be considered a contraindication to attempted endoscopic removal. Kahaleh et al. described two patients with duodenal stenosis that precluded initial ERCP and required a period of enteral feeding to allow resolution of duodenal edema before a duodenoscope could successfully traverse the stenosis. Similarly, some retrieval techniques might be contraindicated, including extraction of uSEMS by means of removing individual stent-wire filaments in patients with coagulopathy and extraction of proximally migrated stents in patients with pericholedocal varices or severe portal hypertension. Furthermore, removal of stents should not be attempted in the following situations:

• Incomplete therapeutic effect and absence of adverse events related to the stent. The stents should not be removed before the beneficial effect is completed if the patient is asymptomatic and the stent is in good position. An exception to this is scheduled stent exchanges before stent occlusion occurs.

• Short life expectancy in an asymptomatic patient. In patients with malignant disease and short life expectancy without symptoms attributable to the biliary stent, there is no need to remove it. It may be reasonable not to try to extract proximally migrated biliary stents in this situation.

Timing of Stent Retrieval

The recommended period that biliary stents should be left in place depends largely on the stent type, stent caliber, and the indication for which the stent is placed. The risk of PBS dysfunction increases with dwell time and is inversely related to the stent's inner diameter. For instance, the median patency of a 10-Fr PBS is estimated at 4 to 5 months, with an occlusion risk that begins to increase progressively after 3 months. Early stent occlusion (within 30 days) is rare and, when present, is more likely to be related to stent malposition/migration, blood clots, or mucinous tumor secretions. More commonly, stent occlusion appears to be directly related to the formation of biofilm; however, a meta-analysis of five randomized controlled trials revealed that the use of choleretic agents and/or antibiotics did not significantly prolong stent patency. In addition, previous studies have suggested that stent composition (i.e., polyurethane vs polyethylene) and shape (i.e., straight vs pigtail) do not appear to affect stent occlusion. If prolonged treatment is required, scheduled stent exchanges are recommended to prevent occlusion-related adverse events, with timing intervals typically dictated by local practice.

With regard to the indication for stenting, the treatment of benign biliary strictures requires that the stent remain in place for a prolonged period, typically no less than 1 year. If PBS (single or multiple) are used, stent replacement is usually performed every 3 months until the end of treatment, though one study suggested that for benign disease and multiple stents, occlusion was uncommon at 3 months and the interval to stent exchange could be increased. SEMS are larger in diameter than PBS and therefore can remain in place for longer periods before removal. In a recent multicenter randomized controlled trial comparing cSEMS to multiple PBS in the treatment of benign biliary strictures, cSEMS were not inferior to PBS in achieving stricture resolution and with fewer ERCPs.

Because of the inherent difficulty of uSEMS retrieval, the use of uSEMS should be limited to patients with malignant disease or those with benign indications but a shortened life expectancy. Although long-term follow-up data on the patency of uSEMS are limited, uSEMS appear to maintain function for a median of 20 months (range 4.5 to 60 months) before reintervention, mostly to address occlusion. If a uSEMS is mistakenly placed under an erroneous context (e.g., misdiagnosis) or has migrated, an attempt at retrieval is indicated. In general, uSEMS retrieval becomes more difficult or even impossible if the duration of dwell time exceeds several weeks because of stent embedment and tissue ingrowth. If removal is unsuccessful, the stents can be mechanically cleaned and additional PBS or SEMS can be placed within the uSEMS; however, this technique will require scheduled maintenance for those with a long life expectancy.

Techniques

Stent removal can be challenging because there are no devices specifically designed for removal other than the Soehendra (Wilson Cook Medical, Winston-Salem, NC) and Carr-Locke (Telemed Systems, Hudson, MA) stent retrievers. The devices most commonly used for stent extraction are polypectomy snares, foreign-body retrieval forceps, and stone extraction baskets. Duodenoscopes with large working channels are recommended if there are multiple stents to remove, there are stents to replace, or bile duct interventions are required. Forward-viewing endoscopes are commonly used when there is a single stent to remove and ERCP is not needed.

For nonmigrated and distally migrated stents, grasping the stent and subsequently removing it through the working channel or simply withdrawing the endoscope while grasping the stent is adequate. Removal of proximally migrated stents is far more difficult and sometimes requires more elaborate devices, intraductal manipulation under fluoroscopic guidance, and, if needed, temporary stenting to ensure ongoing adequate drainage when retrieval is not feasible or is incomplete. During attempted removal, it is important to prioritize patient safety and examination thoroughness with assessment for complete stent retrieval, iatrogenic injury, and resolution of the underlying process that prompted stent placement. Maintaining wire-guided access during the retrieval process can provide safety when intraductal instruments are displaced or biliary orifice visualization becomes impaired from extraction maneuvers.

The choice of retrieval technique is dependent on multiple variables, including the ease of biliary cannulation, presence of biliary duct dilation, type and size of stent requiring retrieval, location of migrated stents, stent impaction, and local expertise. An overview of the more common techniques used for stent retrieval is as follows.

Direct Grasping Technique

The direct grasping technique is a simple technique that involves reaching the second portion of the duodenum with an endoscope and maneuvering a snare to engage the distal intraduodenal end of the stent, which is then tightly grasped and withdrawn from the bile duct. In our experience, comparable to that of other authors, this is the most commonly used technique ( Fig. 24.1 ). A stone extraction basket or foreign-body forceps ( Fig. 24.2 ) can also be used instead of a polypectomy snare; the basket and the forceps are considered equally efficacious ( Video 24.1 ).

These direct grasping techniques are also used to retrieve distally migrated stents. In a recent multicenter study, 17/30 patients suffered symptomatic distal stent migration. Endoscopic removal was attempted and successful in all 17 patients. Retrieval with a snare was employed in 11 of these patients and with a stone extraction basket in the remaining 6 patients.

Indirect Grasping Technique

The indirect grasping technique uses fluoroscopic imaging to assist in positioning intraductal devices in a manner that facilitates grasping and retrieval. The device must be inserted into the bile duct through the papilla, advanced to the stent, and then maneuvered to grasp and pull it down until the stent exits into the duodenum. This has been successfully used in proximally migrated PBS and SEMS. The procedure is most commonly completed by grasping the stent with forceps ( Fig. 24.3 ), although some authors prefer using a snare or stone extraction basket ( Fig. 24.4 ) to retrieve migrated stents.