The current standard treatment of bile duct stones is EST and stone extraction, followed by laparoscopic cholecystectomy if indicated. Surgical procedures such as bile duct exploration and sphincteroplasty, and drainage procedures such as choledochoduodenostomy and hepaticojejunostomy, are options for patients who fail endoscopic therapy[1-3].

Biliary endoprosthesis has been used for biliary drainage as a temporary measure or alternative for patients who are unfit for surgery. Biliary drainage is of great importance in maintaining bile flow in cases of stone impaction in the CBD. Placement of a biliary stent is essential for the treatment or prevention of acute cholangitis in this clinical setting, with a success rate of > 95%[1-3]. This procedure stabilizes the patient so that elective surgery or subsequent endoscopic treatment can be carried out when the patient’s status has improved, thus reducing procedural risks. In elderly patients or patients with severe comorbidities who are poor candidates for further endoscopic or surgical treatments, endobiliary stenting may serve as a permanent therapy; studies report that complication rates associated with surgery in elderly patients range from 12% to 28%[11-15]. In this study, poor surgical candidates who underwent endoscopic biliary stenting showed symptom relief and a low complication rate for more than 1 year, although most patients ultimately developed complications associated with the retained biliary stent itself.

Early outcomes of biliary stenting are well established and include good drainage and a low complication rate, but late outcomes remain uncertain. Most reports revealed that the success rate of endoscopic biliary stenting was nearly 100%, and that early morbidity was low and could be controlled well[16-18]. The major disadvantage of biliary stenting is clogging of the endoprosthesis. It is widely known that the mean patency duration of the plastic biliary stent is about 6 mo to 12 mo for benign diseases[19,20]. Replacement of plastic stents is therefore recommended every 3-6 mo to prevent cholangitis[8,9]. Biliary passage patency is maintained longer when stents are inserted for benign diseases such as biliary stone or benign biliary stricture, as compared to metal stents of malignancies. In this study, biliary stenting was performed for benign diseases, and the mean duration of stent placement was 22.55 ± 12.16 mo before developing symptoms or complications. The plastic biliary stent does not serve as the sole conduit for bile duct flow when used for benign diseases. As a passage between CBD and stent was retained in benign diseases, this passage may provide a conduit for bile flow even when the stent is completely obstructed[10,21,22]. Stent occlusion is the main cause of malignant biliary obstruction, and symptoms and complications occur earlier.

Although biliary patency may be maintained for a longer period after plastic biliary stent insertion, long-standing biliary stents consequentially increase the risk of cholangitis due to formation of biliary stones, because the biliary stent itself may serve as a nidus for stone formation. Lost sphincter of Oddi function, a mechanical barrier preventing regurgitation of duodenal contents into the bile duct, results in bacterial growth in the bile duct by ascending infection and plays an important role in the formation of brown pigment stones[23-25]. All stones in this study appeared to be brown pigment stones. Brown stones were distinguishable by their reddish brown to dark brown color and muddy appearance in macroscopic findings seen at endoscopy.

In this study, 92.1% of patients presented with symptoms of cholangitis, which most often occurred due to development of a CBD stone rather than stent occlusion. Of the 19 patients who underwent stenting for biliary stricture and had no stones initially, 16 patients (84.2%) developed a biliary stone or sludge. In this study, biliary stones were found stuck to biliary stents. Based on this information, the biliary stent may serve as a nidus for stone formation and development, and stent occlusion could develop because of biliary stasis.

Several previous studies showed that biliary patency restoration was successfully achieved in more than 95% of patients with stent obstruction[26]. The follow-up duration for development of complications and clinical symptoms was relatively short in most studies.

Little is known about the complications and management of long-term biliary stents retained more than 1 year. A recent study of 5 cases of long-standing forgotten biliary stents with 45.5 mo (range: 23-84 mo) of stent-stay reported that 4 of them required surgery for treatment[27]. Another recently published article documented that 2 of 3 patients (75%) underwent surgery for treatment of long-stayed forgotten stents[28-30]. In this study, however, 35 of 38 patients (92.1%) with retained long-term biliary stents were successfully treated by endoscopic approach. In 3 cases of endoscopic stent removal failure in patients who were unfit for surgery, cholangitis could be controlled by additional biliary stent placement without surgery.

In conclusion, the most common complication of retained long-term plastic biliary stents was acute cholangitis associated with CBD stones. Endoscopic management was successfully performed in most cases. Biliary patency was likely to be maintained more than 1 year. The rate of complications, such as cholangitis or stent impaction, might be increased as the stent was in place for a longer duration, and CBD stone development ultimately occurred in most cases of long-standing biliary stent. All patients should be informed of the possibility of complications related to retained long-term endoprosthesis placement, and stent change or definite treatment should be considered within 1 year of stent placement. Endoscopic management should be the primary option for the long-term biliary stent, especially in patients with comorbidities or who are unfit for surgery.