Metal Stents for Hilar Lesions

Strictures at the hilum are caused by varied conditions and don’t usually become symptomatic until obstructing the bile ducts, thus posing diagnostic and therapeutic challenges to physicians. ERCP is the method of choice for tissue diagnosis and decompression. MRCP or MRI with dedicated liver protocol provides a unique ability to visualize anatomy and promote procedure planning. In patients with unresectable tumor, endoscopic biliary stenting is a palliative approach. Percutaneous or EUS-guided approach is reserved for endoscopic failure. Various new modalities such as radiotherapy, chemotherapy and Photodynamic therapy have emerged but their superiority needs to be confirmed with Randomized Control studies.

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Growing endoscopic inventions allow us to manage a variety of hilar lesions non-invasively by precluding surgery.
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Although metal stents have been offered for decades for unresectable hilar tumors, innovations such as cross-wired biliary SEMS, PDT, RFA, and EUS-guided biliary drainage have only recently been added to our arsenal.
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Moving forward, multicenter randomized control trials are required to prove their efficacy, thus establishing new standard of care.

Key Points

Introduction

The hilar region is a complex one, containing the biliary, arterial, and venous structures. Stricture at this region can be caused by various benign and malignant causes. Some of the benign causes of hilar stricture include postsurgical injuries from cholecystectomy, liver transplantation or resection, and primary sclerosing cholangitis. Malignant hilar strictures are a group of heterogeneous tumors that include cholangiocarcinoma, tumors involving the hepatic confluence by direct extension from gallbladder, liver, and metastatic cancers. Cholangiocarcinoma is the most frequent cause of malignant hilar lesion, which accounts for only 3% of all the gastrointestinal malignancies. Perihilar cholangiocarcinoma, which involves the confluence of the right and left hepatic ducts, accounts for 60% to 70% of all the cholangiocarcinomas.

Hilar tumor have been classified by Bismuth and colleagues according to the type of involvement of the hepatic ducts. A type I lesion is located below the confluence of hepatic ducts, a type II lesion includes the confluence, type IIIa reaches the first radicals in the right and IIIb involves the radicals on the left, and type IV lesions are multicentric or involve the radicals on both sides. This classification is helpful not only in determining and planning surgical resection but also in endoscopic stent placement. Since originally described in 1965, various advances have been made in both interventional radiology and therapeutic endoscopy that have phenomenally changed the management of these tumors. This review focuses more on the growing indications of using metal stents in unresectable hilar tumors.

Hilar cancers, including cholangiocarcinoma, have an extremely poor prognosis with a 5-year survival rate of less than 10%. The best prognosis with the best long-term survival has been in patients who undergo complete surgical resection with tumor-free margins. This can unfortunately be performed in only 20% of the patients. To increase the number of eligible candidates for surgical resection, a novel technique with preoperative portal vein embolization to cause atrophy of the affected lobe and hypertrophy of normal tissue was evaluated in a bid to attain negative tumor margins. Once the decision for surgical resection is undertaken, the need for preoperative biliary drainage is still controversial, although some literature exists suggesting the need for preoperative biliary drainage via either ERCP or percutaneous transhepatic cholangiography (PTC) to decrease the perioperative mortality and morbidity from cholestasis. The rising complications from the instrumentation of the biliary tree, such as contamination, possible preoperative infection, and inflammation, further increasing the complexity of the surgery are the deal breakers. Further, there is an increasing incidence of tumor seeding associated with a percutaneous approach, secondary to tumor manipulation with passage of a guide wire and a large catheter through the obstructing lesion resulting in the cellular disruption and seeding of the tumor cells through the biliary system. A meta-analysis of 11 studies evaluating the benefit of preoperative biliary drainage with Hilar cholangiocarcinoma also concluded against routine performance of preoperative biliary drainage.

For patients with nonresectable tumors, as mentioned previously palliative biliary drainage is the treatment of choice. This can be performed either via surgery, endoscopic retrograde cholangiopancreatography (ERCP), or PTC. In general, surgical biliary-enteric bypass is not preferred because of increased morbidity. With the rising complications of preoperative biliary drainage and surgical resection, the focus of treatment seems to have shifted to targeted and optimal endoscopic decompression for prolonged symptom-free survival.

The consensus on this still remains controversial, as clinical trials have reported questionable benefits.

Biliary stents

Biliary stents were first introduced in 1979, primarily for palliation of malignant biliary strictures, and then with the introduction of large-channel therapeutic duodenoscopes in 1982, endoscopic insertion of large-diameter plastic biliary endoprostheses became a reality. Higher risks of complications, such as occlusion and migration, associated with the plastic endoprosthesis led to the introduction of expandable metallic stents. Various studies conducted to compare the efficacy of plastic and metallic stents have demonstrated the supremacy of metallic stents in treating malignant biliary strictures. Similarly, even for malignant hilar strictures self-expandable metal stents (SEMS) are preferred, owing to a decrease in frequency of endoscopic sessions and length of hospitalization, along with increased patency rates. Despite their higher costs, they have been proven to be cost-effective in patients who survive more than 4 to 6 months. A retrospective study conducted over 10 years also demonstrated the efficacy of SEMS in palliation of hilar cholangiocarcinoma. Fifty-two metal stent were inserted in 36 patients; 97% of the cases obtained successful internal biliary drainage. Median patency of the stents was 169 days with a low complication rate of 14%. The most interesting observation of the study was that 69% of patients did not require any further biliary reinterventions after initial metal stent placement. Plastic stents are still being used, especially when the diagnosis of cancer is not confirmed, or the patient is a surgical candidate, or is receiving photodynamic therapy or brachytherapy.

Experts have recommended using uncovered SEMS for lesions in the intrahepatic and hilar regions to avoid blocking the drainage of other intrahepatic segments with covered SEMS, as it would lead to segmental cholangitis. Higher rates of migration associated with covered SEMS may possibly be yet another reason for advocating uncovered stents.

Biliary stents

Biliary stents were first introduced in 1979, primarily for palliation of malignant biliary strictures, and then with the introduction of large-channel therapeutic duodenoscopes in 1982, endoscopic insertion of large-diameter plastic biliary endoprostheses became a reality. Higher risks of complications, such as occlusion and migration, associated with the plastic endoprosthesis led to the introduction of expandable metallic stents. Various studies conducted to compare the efficacy of plastic and metallic stents have demonstrated the supremacy of metallic stents in treating malignant biliary strictures. Similarly, even for malignant hilar strictures self-expandable metal stents (SEMS) are preferred, owing to a decrease in frequency of endoscopic sessions and length of hospitalization, along with increased patency rates. Despite their higher costs, they have been proven to be cost-effective in patients who survive more than 4 to 6 months. A retrospective study conducted over 10 years also demonstrated the efficacy of SEMS in palliation of hilar cholangiocarcinoma. Fifty-two metal stent were inserted in 36 patients; 97% of the cases obtained successful internal biliary drainage. Median patency of the stents was 169 days with a low complication rate of 14%. The most interesting observation of the study was that 69% of patients did not require any further biliary reinterventions after initial metal stent placement. Plastic stents are still being used, especially when the diagnosis of cancer is not confirmed, or the patient is a surgical candidate, or is receiving photodynamic therapy or brachytherapy.

Experts have recommended using uncovered SEMS for lesions in the intrahepatic and hilar regions to avoid blocking the drainage of other intrahepatic segments with covered SEMS, as it would lead to segmental cholangitis. Higher rates of migration associated with covered SEMS may possibly be yet another reason for advocating uncovered stents.

Technique

To perform ERCP in these patients with obstruction at the hilar level, it is necessary to do so only after reviewing the prerequisite cross-sectional images to help us delineate the anatomy before proceeding with the procedure ( Fig. 1 ). On reaching the desired segment that needs to be drained based on our imaging, selective cannulation should be performed by advancing the guide wire into the segment over which the catheter is advanced and the contrast is injected proximal to the obstruction ( Fig. 2 ). Contrasts should be injected only in the segments that are planned to be drained and only healthy segments of the liver should be drained. After the initial cannulation, biliary sphincterotomy is performed and the stricture is dilated using either the balloon or dilating catheter and the stents are placed ( Fig. 3 ). During this procedure, choledochoscopy can also be performed to assess and sample the stricture.

The debate of bilateral versus unilateral stenting of the hilar region is still contented, as various studies have revealed conflicting data. Bilateral drainage is a more physiologic than unilateral drainage, but is technically more demanding. This concept of placing multiple stents for obtaining maximal drainage has been supported by many studies that have proven improvement in clinical symptoms and survival. This was challenged by a few other studies. A randomized trial of 157 patients revealed endoscopic success of unilateral over bilateral stenting (89% vs 77%, P = .041) associated with lower rate of complication (27% vs 19%, P = .026) without a change in median survival. Although the verdict is still debatable, in cases of contralateral cholangitis or persistent jaundice with unilateral stenting, then bilateral stenting is mandated. Owing to the difficulties in obtaining the idealistic maximal biliary drainage, different methods have been described in the literature, such as selective placement of guide wires on both sides of the intrahepatic biliary tree : parallel stent deployment, where after guide wire placement on both sides, a plastic stent is placed on first side and SEMS is deployed on the other side, the plastic stent is removed and then exchanged with SEMS; temporary placement of a plastic stent inside the metallic stent to prevent it from fully expanding ; deployment of a second SEMS through the first SEMS after disrupting the interstices ; and use of “open mesh” SEMS with 8-mm interstices in the central section realizing a T-shaped or Y-shaped configuration. With multiple stent placements, there is always a risk of potential entanglement of 2 guide wires, dislodgement of the stents, and difficulty of exact positioning of both the stents to ensure maximal drainage. In an attempt to overcome some of these difficulties, Lee and colleagues conducted a pilot study to evaluate the efficacy of a newly designed Y stent. This was a self-expandable nitinol stent with a central part of Y stent developed as an open mesh to allow for a second stent (Z stent) to be introduced into the contralateral bile duct. Lee and colleagues studied this technique in 10 patients, of whom 8 achieved technical success ( Fig. 4 ). Although there were no immediate complications, stent occlusion developed in 25% of the cases. Recently, SEMS with an easily expandable mid-portion have been evaluated for hilar cholangiocarcinoma. The first SEMS placed has 2 spiral markings in 25 mm of the central portion and has 4 spot markings on both ends (BONASTENT M-Hilar; Standard Sci Tech Inc., Seoul, South Korea). The whole stent has a hook and cross-wired structure with the area between the central spiral markings containing only a cross-wired structured to facilitate expansion and deployment of the second stent. Park and colleagues conducted a multicenter trial with these latest designed stents on 35 patients. They reported an overall success rate of bilateral placement as 33% with an 82% success rate in a single session. Their 6% complication rate compared favorably with the previously reported complication rate.