Benign biliary stricture (BBS) most commonly occurs postoperatively (usually after cholecystectomy and biliary anastomosis following liver transplantation) and secondary to chronic pancreatitis. Endoscopic retrograde cholangiopancreatography (ERCP) has been the first option for relieving biliary obstruction in BBS. The use of plastic stents is a common and widespread treatment to permanently dilate BBS.1 After performing balloon dilatation, insertion of plastic stents is the basic endotherapy, with the aim of inserting the maximum possible number of stents, replacing each stent every 3 months during a 12-month period. Progressive stenting requires a mean number of five ERCP procedures; therefore, it is technically demanding and burdensome but has a mean 80% long-term durable stricture dilation.2

A self-expandable metal stent (SEMS) is a palliative biliary drainage method for unresectable malignant biliary obstructions. SEMSs are proven to have longer patency duration than plastic stents. To overcome the tumor ingrowths in uncovered SEMS, a covered SEMS was developed.

Thus far, there are three different types of SEMS, namely an uncovered SEMS, a partially covered SEMS, and a fully covered SEMS. Application of SEMS in BBS was reported for the first time in 2008.3 Removable SEMSs have been used to achieve permanent BBS dilation. The technique of inserting a fully covered SEMS, which opens to a diameter of 10 mm, is less complex than placing four side by side 10-Fr plastic stents to obtain a 12.8-mm diameter.

Kahaleh et al.3 achieved a 77% success rate using the partially covered SEMS Wallstent (Boston Scientific, Natick, MA, USA). Later, the same author in another study had a 90% success rate at 6 months.4 Tarantino et al.5 reported the efficacy and safety of the nonflared, bumpy, fully covered SEMS Niti-S ComVi (Taewoong Medical, Goyang, Korea) in 62 patients with a variety of BBSs. Among the patients, 82.2% had been refractory to standard plastic stents. The mean period of fully covered SEMS indwelling was 96.7 days, with a mean follow-up period after SEMS removal of 15.9 months. The migration rate was 24.2%. Despite this fact, most BBSs were dilated, with only a 7.1% recurrence rate in transplant recipients. Moon et al.6 reported the use of a short, modified, fully covered SEMS with convex margins placed inside the common bile duct for 3 months. In 21 patients with symptomatic BBS, all the cases were solved after successful stent removal.

The Wallflex fully covered SEMS (Boston Scientific) was also evaluated in a multicenter retrospective study that included 133 patients.7 Stents remained in place for a mean of 96 days. Predictors for success include longer indwelling time (>90 days) and an absence of migration. When a fully covered SEMS is used for benign biliary obstruction, it is important to determine the optimal duration to minimize bile duct injury due to a stent while obtaining adequate remodeling and recanalization of the bile duct.

The goal is to achieve permanent stricture dilation with fewer ERCP procedures than with multiple plastic stents. They also serve as a rescue measure after maximal plastic stent failure. Easy removal of fully covered SEMSs from the bile duct after treatment is of paramount importance. However, because there are few studies on the optimal duration of stent placement during which a fully covered SEMS is efficiently maintained and safely removed, the application of a fully covered SEMS in the treatment of benign disease has been difficult. There are few well-designed animal studies investigating the long-term use of a fully covered SEMS in the bile duct.8 Recently, Lee et al.9 performed an animal study about histological changes of the bile duct after long-term indwelling of a fully covered SEMS for common bile ducts in dogs. They used nitinol wire that is fully covered on both sides with a silicon membrane and a stent with a diameter of 8 mm. Among the 12 animals, de novo stricture was found in five animals. One animal showed severe epithelial hyperplasia, so removal of the stent was impossible even if the stenting period was 3 months. They concluded that a fully covered SEMS might be inserted into the bile duct without severe histopathological changes until 9 months. Of course, the results of this experiment may seem inadequate to determine the optimal duration of placement of a fully covered SEMS in humans.

Fully covered SEMS is an emerging therapy for BBS. It reduces the need for multiple ERCP sessions, and fewer endoscopic skills are needed than for multiple plastic stent placement. Acceptable short-term safety profiles have been demonstrated, although stent migration proves to be a major issue. Cystic and pancreatic duct orifice obstructions are potential complications of fully covered SEMS. Ideal designed fully covered SEMS is warranted to prevent migration and allow easy removal after longer stenting periods. Further prospective randomized studies are needed comparing the efficacy of fully covered SEMSs and plastic stents are needed, and optimal duration of stenting, long-term safety, and cost-effectiveness before routine use can be recommended for BBS.