Biliary Stenting

Etiology

Causes of malignant obstructive jaundice include pancreatic cancer, cholangiocarcinoma, and metastatic disease. Benign causes of obstructive jaundice include acute and chronic pancreatitis, choledocholithiasis, primary sclerosing cholangitis, AIDS cholangiopathy, strictures after invasive procedures, certain parasitic infections, such as Ascaris lumbricoides, Clonorchis sinensis (Chinese liver fluke), Fasciola hepatica, and other liver flukes.

Epidemiology

Pancreatic cancer is the 11th most common cancer, accounting for approximately 3% of all cancers in the United States. While less common, cholangiocarcinoma still accounts for a notable number of cases each year.

Pathophysiology

Pancreatic head cancer and cholangiocarcinoma can lead to obstructive jaundice. While benign diseases may also cause obstructive jaundice, they can still have deleterious effects if not treated promptly. Obstructive jaundice can result in hepatocellular dysfunction, biliary cirrhosis, and an increased risk of cholangitis.

Occlusion of the biliary stent is a common complication, often caused by sludge in plastic or metal stents or tissue overgrowth in self-expanding metal stents (SEMSs). Bacteria can deconjugate bilirubin, producing bilirubinate salts that may contribute to stent occlusion. A double-layer plastic stent with no side holes and an internal coating of perfluoroalkoxy material has been developed to prevent bacterial adhesion. Several plastic stent models include side holes at both ends to maintain drainage if the tip becomes clogged, but these side holes can promote sludge formation. Adding an antireflux valve or applying different coatings to the stent surface are strategies to reduce the risk of stent occlusion.[4][5][6]

Dislodgment of the stent is another common complication, as many covered SEMSs are smooth and provide minimal adherence to the bile duct walls. This issue can be reduced with stents that feature multiple anchoring side flaps and no side holes. These stents, known as "Tannenbaum" stents (German for "fir tree"), help improve stability.

History and Physical

Patients typically present with jaundice, abdominal pain, pruritus, dark urine, clay-colored stools, or signs of infection, such as cholangitis. Other conditions, such as hyperbilirubinemia, may be identified through routine blood work.

Evaluation

Blood work typically reveals elevated bilirubin levels and increased alkaline phosphatase. A computed tomography (CT) scan or magnetic resonance imaging (MRI) of the abdomen is usually performed to identify the cause and location of the obstruction in the biliary tree. Magnetic resonance cholangiopancreatography (MRCP) is a noninvasive imaging technique used to assess both intrahepatic and extrahepatic bile ducts, as well as the pancreatic duct.

Treatment / Management

The treatment algorithm for biliary obstruction and bile leaks involves a combination of endoscopic and percutaneous techniques, tailored to the specific etiology and severity of the condition. Biliary drainage can be achieved through percutaneous transhepatic biliary drainage (PTBD) or endoscopic biliary drainage (EBD). EBD is further categorized into external drainage, such as endoscopic nasobiliary drainage (ENBD), and internal drainage, which involves stent placement. Endoscopic drainage is generally preferred over percutaneous drainage due to its lower complication rate.[7][8][9](A1)

PTBD is performed as an interventional radiology procedure. This access can be utilized for future biliary interventions, such as stone removal with a choledochoscope, biliary stent placement, and treatment of biliary strictures. Both PTBD and ENBD carry several complications and disadvantages, including self-extraction, dislodgment, twisting, and collapse of the tube, as well as patient discomfort and electrolyte imbalances due to the loss of bile and its contents.

Additional complications related to PTBD include bile leakage and pneumothorax. Bile cultures can be obtained through both PTBD and ENBD, if necessary. EBD, however, offers the advantage of minimal patient discomfort and no loss of electrolytes or fluid. The American Society for Gastrointestinal Endoscopy (ASGE) guidelines recommend ERCP with stenting as the primary approach for managing bile leaks and benign strictures, while malignant obstructions may require a SEMS or PTBD.

Biliary stents are made of plastic or metal. While biliary sphincterotomy is not required for the insertion of a single plastic stent or SEMS, if indicated, a blended electrosurgical current should be used. The French (Fr) unit measures the external diameter of biliary stents, with 1 Fr equal to one-third of a millimeter. Most standard duodenoscopes have a 4.2-mm diameter working channel, thereby limiting the introduction of larger plastic stents. The stent length is typically measured from the proximal to the distal flap of the stent.

For the palliation of malignant biliary obstruction, endoscopic biliary stenting offers lower morbidity compared to surgery. SEMSs are generally preferred over plastic stents due to their lower incidence of obstruction after 4 months. Therefore, in patients with a life expectancy of less than 4 months, plastic stents, particularly those measuring 10 Fr in diameter, are more cost-effective. However, if the life expectancy exceeds 4 months, SEMSs are recommended.

In cases where the malignant stricture is resectable, surgery should be performed within a week, with the insertion of a plastic biliary stent to facilitate biliary drainage in preparation for delayed surgery, as this approach carries less morbidity. Preoperative drainage of potentially resectable biliary obstruction is advised only in patients experiencing severe itching, delayed surgery, acute cholangitis, or those undergoing neoadjuvant therapies. SEMSs are preferred in patients receiving neoadjuvant treatments.

Cholecystectomy is the most common cause of biliary leaks, and biliary stenting can effectively manage these leaks. In acute cholangitis, endoscopic sphincterotomy with stone extraction and/or stent insertion is the treatment of choice for biliary drainage. Stents are also useful in managing refractory choledocholithiasis.

Early complications of biliary stenting include infection, bleeding, and pancreatitis. Other complications may involve occlusion caused by sludge in both plastic and metal stents, or tissue overgrowth in SEMSs. Dislodgment occurs more frequently with fully covered SEMSs, with a rate of approximately 20%, followed by plastic stents and partially covered SEMSs at about 5%. This complication is less common with uncovered SEMSs, with a dislodgment rate of around 1%. Dislodgment is more prevalent in benign biliary strictures compared to malignant ones.

Plastic Biliary Stents

Plastic biliary stents vary in length, diameter, shape, material, and cost. They range from 1 to 25 cm in length, with standard models typically between 5 and 18 cm. Longer stents are used in liver transplant patients. The diameters range from 3 to 11.5 Fr, with standard external diameters being 7.0, 8.5, 10.0, and 11.5 Fr. These stents can come in various shapes—straight, curved, wedge, angled, winged, with a single or double pigtail (rarely used), and with center or duodenal bends.

Wedge stents have no flaps, whereas other stents may feature external or internal flaps—single, double, or 4 flaps—to prevent dislocation. S-shaped plastic stents are specifically designed to drain the left biliary tree. Materials used for plastic stents include polyethylene (most common), polyurethane, polyethylene/polyurethane blends, Teflon, and soft polymer blends. Some stents have a construction of an inner Perfluoro layer, a middle stainless steel layer, and an outer polyamide elastomer layer. The European Society of Gastrointestinal Endoscopy (ESGE) advises against Teflon stents due to their lack of softness compared to polyethylene stents.

Self-Expanding Metal Stents

SEMSs vary in length, diameter, design, delivery systems, and materials. The length of the stents ranges from 4 to 12 cm, while the expanded diameter ranges from 6 to 10 mm. The delivery system, typically between 6.5 and 8.5 Fr, uses an outer sheath that is withdrawn after the stent is placed in the duct, allowing it to expand. SEMSs come in various designs, including hook-and-cross, handwoven, and laser-cut. Some SEM models include a retrieval loop, which aids in repositioning or retrieving the stent after placement. SEMSs may be uncovered, partially covered, or fully covered, with coverings made from materials such as silicone, polyether polyurethane, polyurethane, polytetrafluoroethylene, fluorinated ethylene propylene, or polycaprolactone. These coverings facilitate easier extraction of the stent after insertion, an advantage that uncovered stents lack due to tumor ingrowth or benign tissue hyperplasia.

All SEMSs are radiopaque due to their metal alloy composition, most commonly nitinol, which is a combination of nickel and titanium. Nitinol is preferred because it can conform to the lumen. Other metal components may include stainless steel or platinol, which consists of a platinum core encased in nitinol. These metals provide the necessary conformability to the duct, along with adequate radial expansive force. Generally, metal stents are more expensive than plastic stents, which is why plastic stents are preferred in patients with a life expectancy of less than 4 months. However, despite their higher initial cost, SEMSs are associated with a statistically significant lower incidence of occlusion, reduced therapeutic failure, fewer endoscopic reinterventions, shorter hospital stays, and a lower incidence of cholangitis. As a result, SEMSs can ultimately reduce the use of medical resources and lower overall healthcare costs.

Technique of Stent Insertion

Materials required for plastic stent insertion include a radiopaque guidewire, stent insertion system, and dilators. The guidewire typically has a stiffer shaft and a hydrophilic tip to facilitate the passage of strictures. Guidewire systems often feature a locking mechanism to prevent slippage during exchange procedures. Some systems include an intraductal exchange feature, which allows the catheter to be removed while leaving the guidewire in the biliary tract, enabling the insertion of multiple plastic stents. The stent insertion system consists of a plastic guiding catheter (with radiopaque markers), the stent, and a pusher tube. A guiding catheter is not necessary for 7 Fr stents. A balloon catheter or bougie is used to dilate the stricture.

The required stent length is determined based on cholangiography and should be the shortest possible length that ensures adequate drainage. One end of the stent should extend 1 to 2 cm beyond the proximal biliary obstruction, while the other end should be positioned 1 cm into the duodenum. If the intraduodenal portion of the stent is too long, there is a risk of perforation or bleeding ulcers. To begin the procedure, the stent is loaded onto the guiding catheter, which is flushed with saline. The stent insertion system is then introduced into the working channel of the duodenoscope. Once past the stricture, the guiding catheter is disconnected from the pusher tube, and the stent is progressively inserted.

The insertion of the stent is facilitated by rotating the endoscope anticlockwise and gently pulling it. The endoscope should remain near the papilla throughout the procedure to prevent the insertion system from looping in the duodenum. Once the stent is properly positioned, the guidewire and guiding catheter are withdrawn, leaving the pusher tube in contact with the stent to prevent dislocation. An x-ray is obtained to confirm the patency of the stent. The upper end of the stent should be below the cystic duct. In some cases, long plastic stents can be shortened using a snare wire from a lithotripter. Fluoroscopy is used for the insertion of SEMSs, and long SEMSs may be trimmed using argon plasma coagulation.

New stents that require further investigation include antireflux, drug-eluting, bioabsorbable, and magnetic stents. Magnetic stents have been tested in animals, where they can be retrieved using a magnet applied externally, eliminating the need for a second ERCP to remove the stent. However, a concern with magnetic stents is the potential for proximal migration.

Differential Diagnosis

Several conditions should be considered when diagnosing obstructive jaundice, including:

• Alcoholic hepatitis
• Ampullary carcinoma
• Ascariasis
• Bile duct strictures
• Bile dust tumors
• Biliary disease
• Biliary trauma
• Cholangiocarcinoma
• Cholangitis
• Cholecystitis

Complications

Contraindications for biliary stenting include:

• Uncontrolled coagulopathy.
• Severe comorbid conditions.
• Infection: Active cholangitis or sepsis should be managed with antibiotics and drainage before considering stent placement.
• Non-dilated bile ducts: Stenting is generally not indicated in the absence of biliary obstruction or dilation.