Stent
In medicine, a stent is a tube usually constructed of a metallic alloy or a polymer. It is inserted into the lumen of an anatomic vessel or duct to keep the passageway open.
Stenting refers to the placement of a stent. The word "stent" is also used as a verb to describe the placement of such a device, particularly when a disease such as atherosclerosis has pathologically narrowed a structure such as an artery.
A stent is different from a shunt. A shunt is a tube that connects two previously unconnected parts of the body to allow fluid to flow between them. Stents and shunts can be made of similar materials, but perform two different tasks.
There are various types of stents used for different medical purposes. Coronary stents are commonly used in coronary angioplasty, with drug-eluting stents being the most common type. Vascular stents are used for peripheral and cerebrovascular disease, while ureteral stents ensure the patency of a ureter.
Prostatic stents can be temporary or permanent and are used to treat conditions like benign prostatic hyperplasia. Colon and esophageal stents are palliative treatments for advanced colon and esophageal cancer. Pancreatic and biliary stents provide drainage from the gallbladder, pancreas, and bile ducts to the duodenum in conditions such as obstructing gallstones. There are also different types of bare-metal, drug-eluting, and bioresorbable stents available based on their properties.
The term "stent" originates from Charles Stent, an English dentist who made advances in denture-making techniques in the 19th century. The use of coronary stents began in 1986 by Jacques Puel and Ulrich Sigwart to prevent vessel closure during coronary angioplasty.
Stent types
By destination organ
Coronary stent
s are placed during a coronary angioplasty. The most common use for coronary stents is in the coronary arteries, into which a bare-metal stent, a drug-eluting stent, a bioabsorbable stent, a dual-therapy stent, or occasionally a covered stent is inserted.The majority of coronary stents used today are drug-eluting stents, which release medication to prevent complications such as blood clot formation and restenosis. Stenting is performed through a procedure called percutaneous coronary intervention, where the cardiologist uses angiography and intravascular ultrasound to assess the blockage in the artery and determine the appropriate size and type of stent. The procedure is typically done in a catheterization clinic, and patients may need to stay overnight for observation. While stenting has been shown to reduce chest pain and improve survival rates after a heart attack, its effectiveness in stable angina patients has been debated.
Studies have found that most heart attacks occur due to plaque rupture rather than an obstructed artery that would benefit from a stent. Statins, along with PCI/stenting and anticoagulant therapies, are considered part of a broader treatment strategy. Some cardiologists believe that coronary stents are overused, but there is evidence of under-use in certain patient groups like the elderly. Ongoing research continues to explore new types of stents with biocompatible coatings or absorbable materials.
Vascular stent
Vascular stents are a common treatment for advanced peripheral and cerebrovascular disease. Common sites treated with vascular stents include the carotid, iliac, and femoral arteries. Because of the external compression and mechanical forces subjected to these locations, flexible stent materials such as nitinol are used in many peripheral stents.Vascular stents made of metals can lead to thrombosis at the site of treatment or to inflammation scarring. Drug-eluting stents with pharmacologic agents or as drug delivery vehicles have been developed as an alternative to decrease the chances of restenosis.
Because vascular stents are designed to expand inside a blocked artery to keep it open, allowing blood to flow freely, the mechanical properties of vascular stents are crucial for their function: they need to be highly elastic to allow for the expansion and contraction of the stent within the blood vessel, they also need to have high strength and fatigue resistance to withstand the constant physiological load of the arteries, they should have good biocompatibility to reduce the risk of thrombosis and vascular restenosis, and to minimize the body's rejection of the implant.
Vascular stents are commonly used in angioplasty, a surgical procedure that opens blocked arteries and places a stent to keep the artery open. This is a common treatment for heart attacks and is also used in the prevention and treatment of strokes. Over 2 million people receive a stent each year for coronary artery disease alone. Vascular stents can also be used to prevent the rupture of aneurysms in the brain, aorta, or other blood vessels.
Ureteric stent
are used to ensure the patency of a ureter, which may be compromised, for example, by a kidney stone. This method is sometimes used as a temporary measure to prevent damage to a kidney caused by a kidney stone until a procedure to remove the stone can be performed.An ureteral stent it is typically inserted using a cystoscope, and one or both ends of the stent may be coiled to prevent movement. Ureteral stents are used for various purposes, such as temporary measures to prevent damage to a blocked kidney until a stone removal procedure can be performed, providing drainage for compressed ureters caused by tumors, and preventing spasms and collapse of the ureter after trauma during procedures like stone removal. The thread attached to some stents may cause irritation but allows for easy removal by pulling gently.
Stents without threads require cystoscopy for removal. Recent developments have introduced magnetic retrieval systems that eliminate the need for invasive procedures like cystoscopy when removing the stent. The use of magnets enables simple extraction without anesthesia and can be done by primary care physicians or nurses rather than urologists. This method has shown high success rates across different patient groups including adults, children, and kidney transplant patients while reducing costs associated with operating room procedures.
Prostatic stent
s are placed from the bladder through the prostatic and penile urethra to allow drainage of the bladder through the penis. This is sometimes required in benign prostatic hyperplasia.A prostatic stent is used to keep the male urethra open and allow for the passage of urine in cases of prostatic obstruction and lower urinary tract symptoms. There are two types of prostatic stents: temporary and permanent. Permanent stents, typically made of metal coils, are inserted into the urethra to apply constant gentle pressure and hold open sections that obstruct urine flow. They can be placed under anesthesia as an outpatient procedure but have disadvantages such as increased urination, limited incontinence, potential displacement or infection, and limitations on subsequent endoscopic surgical options. On the other hand, temporary stents can be easily inserted with topical anesthesia similar to a Foley catheter, and allow patients to retain volitional voiding. However, they may cause discomfort or increased urinary frequency.
In the US, there is one temporary prostatic stent that has received FDA approval called The Spanner. It maintains urine flow while allowing natural voluntary urination. Research on permanent stents often focuses on metal coil designs that expand radially to hold open obstructed areas of the urethra.
These permanent stents are used for conditions like benign prostatic hyperplasia, recurrent bulbar urethral stricture, or detrusor external sphincter dyssynergia. The Urolume is currently the only FDA-approved permanent prostatic stent.
Colon and Esophageal stents
Colon and esophageal stents are a palliative treatment for advanced colon and esophageal cancer.A colon stent is typically made of flexible metal mesh that can expand and hold open the blocked area, allowing for the passage of stool. Colon stents are used primarily as a palliative treatment for patients with advanced colorectal cancer who are not candidates for surgery. They help relieve symptoms such as abdominal pain, constipation, and bowel obstruction caused by tumors or strictures in the colon.
The placement of a colon stent involves endoscopic techniques similar to esophageal stenting. A thin tube called an endoscope is inserted into the rectum and guided through the colon to locate the blockage. Using fluoroscopy or endoscopic guidance, a guidewire is passed through the narrowed area and then removed after positioning it properly. The stent is then delivered over the guidewire and expanded to keep open the obstructed section of the colon. Complications associated with colon stents include perforation of the intestinal wall, migration or dislodgment of the stent, bleeding, infection at insertion site, or tissue overgrowth around it.
Colon stenting provides several benefits including prompt relief from bowel obstruction symptoms without invasive surgery in many cases. It allows for faster recovery time compared to surgical interventions while providing palliative care for patients with advanced colorectal cancer by improving quality of life and enabling better nutritional intake. However, there are potential risks associated with complications such as migration or obstruction that may require additional procedures or interventions to address these issues effectively.
Pancreatic and biliary stents
Pancreatic and biliary stents provide pancreatic and bile drainage from the gallbladder, pancreas, and bile ducts to the duodenum in conditions such as ascending cholangitis due to obstructing gallstones.Pancreatic and biliary stents can also be used to treat biliary/pancreatic leaks or to prevent post-ERCP pancreatitis.
In the case of gallstone pancreatitis, a gallstone travels from the gallbladder and blocks the opening to the first part of the small intestine. This causes a backup of fluid that can travel up both the bile duct and the pancreatic duct. Gallbladder stones can lead to obstruction of the biliary tree via which gallbladder and pancreas enzymes are secreted into the duodenum, causing emergency events such as acute cholecystitis or acute pancreatitis.
In conditions such as ascending cholangitis due to obstructing gallstones, these stents play a crucial role. They help in maintaining the flow of bile and pancreatic juices from the gallbladder, pancreas, and bile ducts to the duodenum1. Biliary stents are often used during endoscopic retrograde cholangiopancreatography to treat blockages that narrow your bile or pancreatic ducts. In cases of malignant biliary obstruction, endoscopic stent placement is one of the treatment options to relieve the obstruction. Biliary drainage is considered effective, particularly in bile duct conditions that are diagnosed and treated early.