Stents vary in size and material based on their intended use. Though wire mesh cardiac stents implanted into arteries are the most common technology that comes to mind, the basic concept of stenting can be used in a number of other organ systems. Stents are simply tubes that keep a passageway open, and the human body contains a number of non-cardiac passageways.
Esophageal stents are made of either metal or plastic. Self-expanding metal stents (SEMS) are made from stainless steel or a nickel-titanium alloy (nitinol), and four types of SEMS are commercially available according to Medscape. Covered nitinol stents are particularly useful for patients with dysphagia (which occurs with inoperable esophageal cancer, tracheo-esophageal fistulas, and anastomotic leaks) according to a research study summarized by ScienceDaily. The study comparing self-expanding metal esophageal stents was published in World Journal of Gastroenterology in May 2010.
A 2005 study in the Journal of Vascular and Interventional Radiology found that esophageal disorders benefit more from temporary stenting than permanent stenting. Strictures are treated with plastic stents (silicone covered polyester is one type) until other corrections, such as surgery, can be performed or the passageway remains open on its own.
Biliary (Bile duct) Stents
Blocked bile ducts can lead to jaundice and digestive complications. Stent placement is often less risky than surgery according several clinical trials summarized by Medscape. Two types of biliary stents are generally available for use by surgeons: the more common polyethylene (plastic) stent, and the larger diameter metal stents. The plastic stents come in a variety of lengths and diameters and have flaps that help prevent migration after insertion. The metal stents are generally self-expanding mesh with hooks, allowing permanent placement. Plastic stents are used for temporary stenting of the bile ducts because long-term use can increase the risk of re-stenosis and infection as described in a 2007 study.
Ureter stents help open the ureters, the ducts between the kidneys and bladder. Stenting may be used for the short-term or long-term (up to 3 months) depending on the patient’s needs. Temporary stenting generally uses open-ended stents, whereas long-term stenting benefits from coiled (pigtail) stents to avoid passing them with the urine according to the Surgery Encyclopedia. Ureteral stents are flexible and made of polymers (plastic). The materials are compared and described in a review in the World Journal of Urology.
The urethra is the duct between the bladder and external environment. Urethral stents also aid in the flow of urine. Duvdevani, Chew, and Denstadt from the Division of Urology at the University of Western Ontario published a review of the current stent technology for re-opening the urethra in January 2010. The stenting is also used for prostate obstructions as the ducts are connected in men.
Urethral stents are usually made of polyurethane, though stainless steel stents are used for the prostate and temporary stenting. However, a broad variety of stents are available, including ones made from nitinol and gold-plated stainless steel.
Rectal stents are still a relatively rare treatment. The first use of self-expandable colorectal stents was reported in 1991. Stents have been used to alleviate rectal and blockage caused by inoperable colon cancer. They are generally in place until the patient succumbs to the disease. A study in the Korean Journal of Radiology compared various types of covered (by polyurethane) and non-covered metal stents with two different shapes (flare and shoulder) in 2002 for alleviating intestinal blockage.