A stent is a small, tube-shaped device that medical professionals insert into a blocked or narrowed passage within the body. Its fundamental purpose is to hold the passageway open, restoring the flow of fluids or substances. These devices are typically made from metal or plastic, and their design can vary depending on the specific anatomical location and medical need. Stent placement is a common medical procedure, often performed to alleviate blockages caused by conditions such as plaque buildup in blood vessels.
Bare Metal Stents
Bare metal stents (BMS) represent a foundational advancement in interventional medicine, introduced in 1986 to address limitations of balloon angioplasty. These thin, mesh-like tubes are made from metallic alloys, commonly stainless steel or cobalt-chromium. Their mechanism of action relies purely on mechanical support, physically propping open a narrowed vessel to maintain its patency. Over time, the inner lining of the artery grows over the stent, integrating it as a permanent part of the vessel. While BMS significantly improved outcomes compared to balloon angioplasty by reducing acute vessel closure, they carried a notable risk of restenosis, which is the re-narrowing of the treated vessel due to scar tissue growth within the stent. This could occur in up to 30% of patients.
Drug-Eluting Stents
Drug-eluting stents (DES) combat restenosis, the re-narrowing of an artery after stenting, by releasing specific medications from a polymer coating on their metallic framework. These drugs, such as sirolimus or paclitaxel, inhibit excessive scar tissue growth (neointimal hyperplasia) that can lead to re-blockage. Localized drug delivery reduces restenosis incidence to less than 10%, a substantial improvement over bare metal stents, while avoiding systemic toxicity and maintaining physical scaffolding. DES are widely used, particularly in the treatment of coronary artery disease, where plaque buildup narrows the arteries supplying the heart. Patients with DES require antiplatelet medications for an extended period to prevent blood clots.
Bioabsorbable Stents
Bioabsorbable stents, also referred to as bioresorbable or dissolvable stents, offer a unique approach by disappearing from the body over time. These stents are typically crafted from naturally dissolvable polymers, such as polylactide, similar to materials used in dissolving stitches. The core concept behind their design is to provide temporary scaffolding for a healing vessel and then degrade, leaving no permanent implant behind. Benefits include restoring vessel flexibility, allowing future interventions, and avoiding long-term complications of permanent metallic implants, such as chronic inflammation or late stent thrombosis. While promising, bioabsorbable stents have faced challenges, and their adoption is not as widespread as metallic stents. They are an evolving technology, with research focused on improving mechanical performance and ensuring outcomes comparable to drug-eluting metallic stents.
Covered Stents
Covered stents differentiate themselves from open-mesh designs by incorporating a fabric or membrane covering over their metallic framework. This covering provides a barrier that changes their function compared to other stent types. The design allows them to seal off perforations, which are small holes or tears in a vessel wall, or to prevent leakage. These stents are particularly useful in specific scenarios where a plain scaffold would not suffice. For example, they are employed to treat aneurysms, which are bulges in a vessel wall that could rupture, by providing a new lining to reinforce the weakened area. Covered stents also find application in containing leaks in various vessels, ensuring that fluids flow only through the intended pathway.
Stents for Non-Vascular Applications
Stents serve a broader purpose beyond cardiovascular health, extending their utility to various non-vascular anatomical locations. Esophageal stents are placed in the food pipe to alleviate blockages, commonly caused by tumors or strictures, making it easier for patients to swallow liquids and soft foods; these can be self-expanding metal stents or plastic stents, depending on the condition. Biliary stents keep bile ducts open, which are tubes that transport bile from the liver and gallbladder to the small intestine; blockages in these ducts can lead to serious digestive issues. Urethral stents address obstructions in the ureters, the tubes carrying urine from the kidneys to the bladder, ensuring proper urine flow. Tracheal or bronchial stents are deployed in the airways to treat narrowing that can impede breathing, providing structural support.