In medicine, a stent is a tube that is inserted into a natural conduit of the body to prevent or counteract a disease-induced localized flow constriction. The term may also refer to a tube used to temporarily hold such a natural conduit open to allow access for surgery.
The main purpose of a stent is to counteract significant decreases in vessel or duct diameter by acutely propping open the conduit by a mechanical scaffold or stent. Stents are often used to alleviate diminished blood flow to organs and extremities beyond an obstruction in order to maintain an adequate delivery of oxygenated blood. Although the most widely known use of stents is in coronary arteries
, they are widely used in other natural body conduits, such as central and peripheral arteries
, bile ducts
or large bronchi
, and urethra
The origin of the word stent
remains unsettled. The verb stenting
was used for centuries for the process of stiffening garments (a usage long obsolete, per the Oxford English Dictionary
) and some believe this to be the origin. Others attribute the noun stent
to Jan F. Esser
, a Dutch plastic surgeon who in 1916 used the word to describe a dental impression compound invented in 1856 by the English dentist Charles Stent
(1807–1885), which Esser employed to craft a form for facial reconstruction. The full account is described in the Journal of the History of Dentistry
. According to the author, from the use of Stent's compound as support for facial tissues grew the eventual use of stent to open various bodily structures.
Worth noting though is that the first "stents" used in medical practice were initially called "Wallstents".
Types of stent
The most widely known stent use is in the coronary arteries with a bare-metal stent, a drug-eluting stent or occasionally a covered stent.
Coronary stents are placed during a percutaneous coronary intervention procedure.
Ureteral stents 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 blocked kidney, until a procedure to remove the stone can be performed. Indwelling times of 12 months or longer are indicated to hold ureters open, which are compressed by tumors in the neighbourhood of the ureter or by tumors of the ureter itself. In many cases these tumors are inoperable and the stents are used to ensure drainage of urine through the ureter. If drainage is compromised for longer periods, the kidney can be damaged. The main complications with ureteral stents are dislocation, infection and blockage by encrustation. Recently stents with coatings (e.g. heparin) were approved to reduce infection, encrustation and therefore stent exchanges.
A urethral or Prostatic stent might be needed if a man is unable to urinate. Often this situation occurs when an enlarged prostate pushes against the urethra, blocking the flow of urine. The placement of a stent can open the obstruction, avoiding the collapse of the urethra.
Stents are used in a variety of vessels aside from the coronary arteries.
Stents may be used as a component of peripheral artery angioplasty
A stent graft is a tubular device, which is composed of special fabric supported by a rigid structure, usually metal. The rigid structure is called a stent. An average stent on its own has no covering, and therefore is usually just a metal mesh. Although there are many types of stent, these stents are used mainly for vascular intervention.
The device is used primarily in endovascular surgery. Stent grafts are used to support weak points in arteries, commonly known as an aneurysm. Stent grafts are most commonly used in the repair of an abdominal aortic aneurysm, in a procedure called an EVAR. The theory behind the procedure is that once in place inside the aorta, the stent graft acts as a false lumen for blood travel through, instead of into the aneurysm sack.
Risks associated with vascular stents
Executive function has been demonstrated to decline in patients who undergo coronary artery bypass as well as individuals who receive vascular stents. The mechanism of action for cognitive decline in bypass surgery is believed to be due to the release of tiny emboli into the blood stream that subsequently travel into the brain resulting in small strokes or ischemia. While the same degree of decline in executive function or 'IQ' occurs in vascular stenting of the coronary arteries, the mechanism of action remains unknown. This decline from pre-procedure baseline has been observed soon after surgery and as far out as six years post surgery. While the decline is minimal, it is measurable, consistent and appears to be permanent. Lifestyle modifications to treat elevated cholesterol, diabetes and hypertension offer the safest course of action in treating non-life threatening coronary artery disease.
- CHD Stent
- Rectal Stent
- Oesophageal Stent
- Biliary Stent
- Pancreatic Stent