Biliary Stenting

Etiology

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

Epidemiology

Pancreatic cancer is the 11th most common cancer and accounts for about 3% of all cancers in the United States. Cholangiocarcinoma is not as common, but it still accounts for a reasonable number of cases per year.

Pathophysiology

Pancreatic head cancer and cholangiocarcinoma result in obstructive jaundice. Although benign diseases may be the cause of obstructive jaundice, they still have deleterious effects if not treated promptly, as obstructive jaundice would lead to hepatocellular dysfunction, biliary cirrhosis and increases the incidence of cholangitis. 

Occlusion of the biliary stent is a common complication caused by sludge in plastic or metal stents or by tissue overgrowth in self-expanding metal stents (SEMSs). Bacteria have the ability to deconjugate bilirubin, producing bilirubinate salt that may lead to stent occlusion. To prevent bacterial adhesion, a double-layer plastic stent with no side holes and with an internal coating of perfluoroalkoxy material was developed. Several plastic stent models have side holes at both ends to continue drainage if the tip of the stent is clogged; however, these side holes may favor sludge formation. Adding an antireflux valve or use of different coatings on stent surface are ways to avoid stent occlusion.[4][5][6]

Dislodgment of the stent is another common complication as many of the covered SEMSs are smooth, thus causing little adherence to the bile duct walls. This complication is lessened through stents with multiple anchoring side flaps and with no side holes. These stents with multiple side flaps are known as “Tannenbaum” stents, German for "firtree."

History and Physical

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

Evaluation

Blood work would show elevated bilirubin level and elevated alkaline phosphatase. A CT scan or MRI of the abdomen would probably show the cause and site of obstruction in the biliary tree. Magnetic resonance cholangiopancreatography (MRCP) is a noninvasive technique to evaluate the intrahepatic and extrahepatic bile ducts and the pancreatic duct.

Treatment / Management

Biliary drainage can be either percutaneous transhepatic biliary drainage (PTBD) or endoscopic biliary drainage (EBD). EBD is of 2 types: external drainage which is endoscopic nasobiliary drainage (ENBD) and internal drainage which is stent placement. Endoscopic drainage is superior to percutaneous drainage because of less complication rate.[7][8][9](A1)

PTBD is done as an interventional radiology procedure. This access may be used in the future for biliary interventions such as stone removal with a choledochoscope, placement of biliary stents, and treatment of biliary strictures. Both PTBD and ENBD have several complications and disadvantages including self-extraction, dislodgment, twisting, and collapse of the tube, patient discomfort and electrolyte abnormalities secondary to loss of bile and its contents. Other complications related to PTBD include bile leakage and pneumothorax. Bile cultures can be done, if needed, through these 2 approaches. On the other hand, endoscopic biliary drainage has the advantage of lack of discomfort for the patient and no loss of electrolytes or fluid.

Biliary stents are made of plastic or metal. Biliary sphincterotomy is not required for inserting a single plastic stent or self-expanding metal stent (SEMS), but if indicated, blended electrosurgical current needs to be used. The French (Fr) is the unit of measurement of the external diameter of biliary stents and is equal to one third of a millimeter. Most standard duodenoscopes have working channels that are 4.2 mm in diameter, which makes it impossible to introduce larger plastic stents through. The stent length is usually the distance between the proximal and distal flaps of the stent.

For palliation of malignant biliary obstruction, endoscopic biliary stenting carries a lower morbidity than surgery. Generally speaking, SEMSs are preferred to plastic stents because of decreased incidence of stent obstruction at 4 months. Therefore, in these patients, if life expectancy is less than 4 months, plastic stents are indicated as this would be more cost-effective, especially those measuring 10 Fr in diameter. If life expectancy is longer than 4 months, SEMSs are recommended. On the other hand, if the malignant stricture is resectable, surgery within a week (to insert a plastic biliary stent for biliary drainage preparing for delayed surgery) is recommended, as it carries less morbidity. Preoperative drainage of potentially resectable biliary obstruction is recommended only in patients with severe itching and delayed surgery, in patients with acute cholangitis, or in patients who would undergo neoadjuvant therapies. SEMSs are recommended in those patients undergoing neoadjuvant therapies.

Cholecystectomy is the most common cause of biliary leaks, and biliary stenting can be used to treat these leaks. In acute cholangitis, endoscopic sphincterotomy with stone extraction and/or stent insertion is the treatment of choice for biliary drainage. Stents can also help with management of refractory choledocholithiasis.

Early complications of biliary stenting include infection, bleeding, and pancreatitis. Complications of biliary stents include occlusion caused by sludge in both types of stents or by tissue overgrowth in SEMS. Dislodgment happens more frequently at 20% of the time with fully covered SEMSs, followed by plastic stents and partially covered SEMSs approximately 5% of the time. This complication is not as frequent with uncovered SEMSs with a rate of 1%. Dislodgment happens with benign biliary strictures more often than with malignant strictures.

Plastic biliary stents differ in length, diameter, shape, material, and price. They range from 1 to 25 cm in length, but standard models range from 5 to 18 cm. Longer models are used in liver transplant patients. They range from 3 to 11.5 Fr in diameter. Standard external diameters of plastic biliary stents are 7.0, 8.5, 10.0, and 11.5 Fr. They can be straight, curved, wedge, angled, winged, with single or double pigtail (rarely used), and with center bend and/or duodenal bend. Wedge stents have no flaps. Other stents have flaps which can be external or internal, with single, two or four flaps, to prevent dislocation. S-shaped plastic stents are particularly designed to drain the left biliary tree. The stents are made up of polyethylene (most common), polyurethane, polyethylene/polyurethane blend, Teflon or soft polymer blend. Some types of stents are made of an inner layer of Perfluoro, a middle layer of stainless steel and an outer layer of polyamide elastomer. European Society of Gastrointestinal Endoscopy (ESGE) recommends against Teflon stents as they are not as soft as Polyethylene stents.

Likewise, SEMSs have different lengths, diameters, designs, delivery systems, and materials. Length of the stents ranges from 4 to 12 cm. Diameters, when expanded, range from 6 to 10 mm. The delivery system ranges from 6.5 Fr to 8.5 Fr, done through an outer sheath, and is withdrawn after placing the stent in the duct, allowing the stent to expand. SEMSs have different designs: hook and cross, hand woven, laser cut, and some have a retrieval loop, that helps with repositioning or retrieval of the stent after placement. SEMSs may be uncovered, partially covered, or fully covered SEMSs. Coverings include silicone, polyether polyurethane, polyurethane, polytetrafluoroethylene fluorinated ethylene propylene, or polycaprolactone. Coverings allow easier extraction of stents after being inserted, an advantage which uncovered stents lack because of tumor ingrowth or benign tissue hyperplasia. All SEMSs are radiopaque as they are made up of metal alloys most commonly nitinol which is a combination of nickel and titanium. This is the metal of choice because it can conform to the lumen. Other metal components include stainless steel or platinol which is platinum core with nitinol encasement. These metals allow for conformability to the duct along with adequate radial expansile force. Generally speaking, metal stents are more expensive than plastic stents, and hence, the preference for plastic stents in patients with life expectancy less than 4 months. However, despite their higher initial cost, SEMSs are associated with a statistically significant lower incidence of occlusion, less therapeutic failure, thus less need for endoscopic reintervention, decreased length of hospital stay, and lower cholangitis incidence. Thereby, SEMSs would eventually decrease use of many medical resources and reduce overall health cost.

Technique of Stent Insertion

Materials required for plastic stent insertion include radiopaque guidewire, stent insertion system and dilators. The guide wire most often has a stiffer shaft and a hydrophilic tip to make passage of strictures easier. Guidewire systems have a locking mechanism to prevent the wire from slipping during exchange procedures. They may have intraductal exchange that allows for removing the catheter while leaving the guide wire in the biliary tract, thus insertion of multiple plastic stents would be feasible. Stent insertion system consists of a plastic guiding catheter (with radiopaque markers), stent, and pusher tube. A guiding catheter is not required for 7 Fr stents. A balloon catheter or bougie is used to overcome a stricture.

The required stent length is assessed based on cholangiography and should be the shortest possible that allows adequate drainage. One end of the stent should be 1 to 2 cm beyond the proximal biliary obstacle and the other end should be 1 cm into the duodenum. If the intraduodenal portion of the stent is long, perforation or bleeding ulcer may happen. The stent is loaded onto the guiding catheter, which is flushed with saline. The stent insertion system is introduced into the working channel of the duodenoscope. The guiding catheter is then disconnected from the pusher tube after going past the stricture and the stent is progressively inserted. Stent insertion is made easier through anticlockwise rotation and pulling of the endoscope. The endoscope has to be near the papilla throughout the procedure to avoid looping of the insertion system in the duodenum. When the stent is in the proper position, the guide wire and the guiding catheter are withdrawn leaving the pusher tube in contact with the stent to prevent dislocation. An X-ray is obtained to verify patency. The upper end of the stent should be below the cystic duct. Long plastic stents can be shortened by a snare wire of a lithotripter. Insertion of SEMS is done under fluoroscopy. Long SEMSs may be trimmed using argon plasma coagulation.

New stents that need further investigation include antireflux stents, drug-eluting stents, bioabsorbable stents, and magnetic stents. Magnetic stents have been investigated and tested in animals where the stent can be retrieved using a magnet held from outside the body, thus obviating the need for a second ERCP to remove the stent. The concern was with the possibility that the stent may migrate proximally.

Differential Diagnosis

• Alcoholic hepatitis

• Ampullary carcinoma

• Ascariasis

• Bile duct strictures

• Bile dust tumors

• Biliary disease

• Biliary trauma

• Cholangiocarcinoma

• Cholangitis

• Cholecystitis