A medical stent is a small, hollow tube placed inside a natural passage in the body to keep the pathway open. In the digestive system, stents are often used to relieve blockages in the biliary system, the network of ducts that transports bile. Unobstructed flow is required for proper bodily function. When these ducts become narrowed or blocked, a stent provides an internal scaffold to maintain drainage and prevent serious complications.
Understanding Biliary Obstruction
The biliary system moves bile, a fluid produced by the liver that aids in fat digestion and waste removal, from the liver to the small intestine. Bile travels through a series of ducts, including the common bile duct. The gallbladder temporarily stores and concentrates bile before releasing it into the small intestine after a meal.
When the bile ducts become blocked, the normal flow of bile is interrupted, leading to a condition called biliary obstruction. This blockage causes bile and its waste product, bilirubin, to back up into the liver and bloodstream. The most visible result of this buildup is jaundice, characterized by the yellowing of the skin and eyes.
A lack of drainage can also lead to serious complications, such as cholangitis, a severe bacterial infection of the bile ducts. If the obstruction is near the gallbladder, the resulting pressure can cause swelling and inflammation, known as cholecystitis. Stenting restores the flow and alleviates this backlog of bile.
Medical Conditions Requiring Stenting
Stents are placed in the biliary system to relieve obstruction caused by malignant or benign conditions. Malignant obstruction is the most frequent reason for stenting, often due to cancers that press on or invade the bile ducts. Common causes include cancers of the pancreas, bile duct (cholangiocarcinoma), and metastatic tumors.
For cancer patients, stenting often serves as a palliative measure to relieve symptoms like jaundice and itching, improving quality of life when the tumor is inoperable. Restoring bile flow before surgery or chemotherapy improves liver function, allowing patients to tolerate treatment. Stents may also be placed preoperatively to temporarily decompress the system before planned surgical removal.
Beyond cancer, stents are used to manage benign strictures, which are non-cancerous narrowings of the bile ducts. These strictures can arise from chronic inflammation, such as that seen in chronic pancreatitis, or from scarring that occurs after surgery, particularly gallbladder removal. In these cases, a stent is used to physically widen the narrowed segment and keep the duct patent.
Stenting is also a temporary solution in acute, high-risk scenarios, such as severe cholecystitis in patients too frail for immediate surgery. While the stent is usually placed in the common bile duct to relieve system pressure, a tube may be placed directly into the gallbladder (cholecystostomy) for drainage. This temporary drainage stabilizes the patient, allowing inflammation to subside before definitive treatment.
How the Stent is Placed
Biliary stents are typically placed using minimally invasive, image-guided techniques. The most common method is Endoscopic Retrograde Cholangiopancreatography (ERCP). During ERCP, a flexible, lighted tube called an endoscope is inserted through the mouth, down the esophagus, and into the duodenum, the first part of the small intestine.
The doctor locates the small opening where the bile duct empties into the duodenum. A thin wire, called a guidewire, is then advanced through the endoscope and carefully threaded past the blockage and into the bile duct under X-ray guidance. The stent is pushed over this guidewire and deployed across the narrowed segment.
If ERCP is unsuccessful due to complex anatomy or a complete blockage, an alternative method called Percutaneous Transhepatic Cholangiography (PTC) may be used. In PTC, a doctor inserts a thin needle through the skin of the abdomen, past the liver, and directly into a bile duct. A contrast dye is then injected to visualize the biliary tree on X-ray.
The stent is guided through this needle tract and deployed across the stricture. Both ERCP and PTC allow the stent to be placed internally, bypassing the obstruction to restore bile flow into the small intestine. The choice between the two methods depends on the patient’s condition and the location of the blockage.
Types of Stents and Post-Procedure Care
The two main types of stents used in the biliary system are defined by their material: plastic and metal. Plastic stents are generally less expensive and are made from materials like polyethylene or polyurethane. They are typically used for short-term relief, such as temporary drainage or in cases of benign strictures that require repeated exchanges.
Plastic stents have a smaller diameter, making them prone to clogging with bile sludge and bacteria, often requiring replacement within three to six months. Conversely, metal stents, specifically Self-Expanding Metal Stents (SEMS), are typically made of alloys like nitinol and have a larger diameter. They are designed for long-term use and are preferred for patients with malignant obstructions.
Following the procedure, patients are monitored for potential complications, including infection, stent migration, or occlusion. The most common long-term issue is the stent becoming blocked, causing symptoms of obstruction, like jaundice and fever, to return. This necessitates a follow-up procedure to clear the blockage or exchange the stent.
The type of stent dictates the follow-up schedule; plastic stents require routine replacement, while metal stents are often left in place permanently in cases of malignant disease. Regular monitoring and timely intervention for any complications are necessary.