Carotid stenosis is the medical description of the narrowing or constriction of the carotid artery. The artery is located in the neck, and the narrowing of the artery is caused by the buildup of plaque (fatty deposits). The process of atherosclerosis causes a hardening of the walls of the arteries and, in the case of atherosclerosis in the carotid artery, results in a carotid stenosis that reduces the flow of blood and nutrients to the brain.
The carotid arteries run up the sides of the neck. They are vital arteries, and are a route of blood to the anterior part of the brain and, via branches, to the eyes, forehead, and nose. The deposition of plaque along the inner wall of an artery narrows its diameter. This makes the clogged artery less efficient in transporting blood. Plaque formation can become so severe that an artery is effectively blocked.
Carotid stenosis poses another danger when bits of the plaque dislodge. These pieces, which are referred to as blood clots or emboli, can move upward with the flow of blood towards the brain and can become lodged, blocking blood flow. This blockage interrupts the supply of nutrients and oxygen to the brain, and is one of the causes of cerebral vascular accidents, known as stroke. Carotid stenosis is a form of cerebral vascular disease and atherosclerosis.
Stroke is the third leading cause of death in the United States after coronary artery disease and cancer, with approximately 750,000 strokes and more than 150,000 deaths occurring each year in the United States. Approximately 50% of these strokes are thought to be the result of carotid stenosis.
Causes and symptoms
The cause of carotid stenosis is the buildup of plaque on the inner wall of the carotid artery. The reduced blood flow to the brain and the blockage of other arteries following the release of emboli can cause a stroke. Increased risk of carotid stenosis is associated with smoking, hypertension, elevated levels of cholesterol, obesity, and a sedentary lifestyle. Some of these factors such as hypertension and cholesterol level may also be related to a person's physiology. Another risk factor is diabetes. Older, less active people are more prone to carotid stenosis. Additionally, the older a person is, the greater the risk posed by carotid stenosis.
Sometimes, prior to a major stroke, a person can be temporarily affected by the arterial blockage or release of a small embolus. The interrupted flow of blood to the brain, which can be very brief or last a few hours, does not persist longer than 24 hours. Symptoms of this transient event, called a transient ischemic attack (TIA), include weakness, as well as visual and speech difficulties. The exact symptoms of carotid stenosis depend on the area of the brain that is affected. Symptoms can also be absent, with the stenosis discovered only incidentally during a clinical examination.
In the event of a stroke, if the blocked blood flow is not restored, brain cells can die, causing permanent brain damage.
Although not as accurate as other methods, a physician can listen to the pulsing of blood through the carotid artery by means of a stethoscope. The weaker pulse that is a result of stenosis will be evident in the form of altered sounds (bruits) as the blood flows past the area of disturbance.
Sometimes, carotid stenosis is suspected if a person has a transient malfunction of blood flow to the brain, or a TIA. A TIA can last anywhere from a few seconds to several hours. The temporary blockage of the artery can
cause a momentary loss of vision in one eye, a weak or numb sensation on one side of the body, slurred speech, or inability to speak. A TIA can be a warning to a physician of the potential presence of carotid stenosis.
Three main diagnostic tests aid in the diagnosis of carotid stenosis. The first is known as a duplex sonogram, or a carotid duplex. The procedure involves the use of highfrequency sound waves (ultrasound). The ultrasonic waves echo off of the carotid artery to produce a two-dimensional image on a monitor. If narrowing or obstruction of the carotid artery is present, it is often apparent in the image.
Another powerful imaging technique is magnetic resonance imaging (MRI) or magnetic resonance angiography (MRA). Both rely on the use of magnetism. Pulses of magnetic energy can be used to image the targeted area of the body, based on the interruption of the flow of the electrons in the magnetic field. This information is then converted to a visual image.
The third technique is known as an angiogram or arteriogram. An angiogram is an examination that utilizes x rays after a small tube (catheter) is inserted into the base of the carotid artery. An x-ray dye is then injected. The dye reveals the areas of the regions of the artery that are narrowed or blocked.
Carotid stenosis is treated surgically or medically. One of two surgical treatments is typically used. The first approach is known as microsurgical carotid endarterectomy. The second approach is termed endovascular angioplasty and stenting.
Carotid endarterectomy is the surgical exposure of the carotid artery and the removal of the plaque. This re-establishes the uninterrupted flow of blood to the brain. This approach is the method of choice for most patients. However, the technique does itself carry a risk of stroke (stroke can be caused in up to 3% of surgeries).
For patients who are unable to undergo surgery, the angioplasty and stenting approach is used. In this approach a catheter that contains an expandable region at one end is inserted into the carotid artery. The end of the catheter is then expanded. This "balloon" squeezes the plaque against the arterial wall, increasing the effective diameter of the artery. Then, a stent is placed inside the artery. A stent is a tubular arrangement of fibers somewhat similar visually to wire fencing rolled up into a tube. The stent reinforces the carotid artery to prevent its collapse and to keep the plaque tightly against the arterial wall.
Surgery and the associated risks may not be warranted in patients whose arterial blockage is less than 50%.
As of February 2004, a clinical trial designed to investigate the relative effectiveness of carotid angioplasty with stenting versus carotid endarterectomy in preventing stroke, myocardial infarction, and death was recruiting patients in the United States and Canada. Participants should have symptoms of carotid stenosis. The trial, called "Carotid Revascularization Endarterectomy versus Stent Trial (CREST)," was being coordinated by the National Institute for Neurological Diseases and Stroke.
Another clinical trial was designed to examine the role of diet (specifically high doses of vitamin E) on the metabolism of low-density lipoprotein, which is critical in plaque formation. This trial was being coordinated by the National Institute of Health's National Center for Complimentary and Alternative Medicine. Information on both clinical trials may be found at the National Institute of Health Clinical Trials website: www.clinicaltrials.gov.
With prompt medical treatment, including surgery, recovery from carotid stenosis can be complete with no residual effects. However, if treatment is delayed or if a stroke occurs, damage can be permanent.
If carotid stenosis is dealt with promptly by surgery, medicine, or lifestyle modifications, prognosis is good. For example, at the Johns Hopkins Medical School, carotid stenosis corrective surgery has a mortality rate of 0.8% (80 in 1,000 people) and a morbidity rate (the person survives, but with some complication) of 1.8% (18 in 1,000 people).
However, undiagnosed stenosis can result in stroke. Depending on the severity of the stroke, prognosis is variable. An estimated 325,000 strokes and 75,000 deaths occur each year in the United States due to carotid stenosis.
Even if there are no symptoms associated with the presence of carotid stenosis, the malady is often a warning sign of possible blockage of the arteries of the heart, or coronary artery disease. Thus, people diagnosed with carotid stenosis should be carefully monitored for coronary artery disease.
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Johns Hopkins Department of Neurosurgery. "What is Carotid Stenosis?" Johns Hopkins University School of Medicine. (February 1, 2004). <http://www.neuro.jhmi.edu/cerebro/cs.html>.
"Risk Reduction through Surgery: Carotid Endarterectomy." National Stroke Association. (March 1, 2004). <http://18.104.22.168/NationalStroke/StrokePrevention/Risk+Reduction+through+Surgery.htm>.
Toronto Brain Vascular Malformation Study Group. "Carotid Stenosis. What is Carotid Stenosis?" University of Toronto. (February 1, 2004).<http://brainavm.uhnres.utoronto.ca/malformations/content/carotid_stenosis.htm>.
American Stroke Association, a division of the American Heart Association. 7272 Greenville Avenue, Dallas, TX 75231. (888) 4-STROKE. <http://www.strokeassociation.org>.
Centers for Disease Control and Prevention (CDC). 1600 Clifton Road, Atlanta, GA 30333. (404) 639-3311 or (800) 311-3435. <http://www.cdc.gov>.
National Institute for Neurological Diseases and Stroke (NINDS). 6001 Executive Boulevard, Bethesda, MD 20892. (301) 496-5751 or (800) 352-9424. <http://www.ninds.nih.gov>.
Brian Douglas Hoyle, PhD