A stroke is any sudden event affecting the brain’s blood supply. The most common type, almost 80% of all strokes, is ischemic stroke, where the blood supply to the brain is cut off or severely reduced due to a blocked artery. A condition known as stenosis contributes to an individual’s risk for this type of stroke.
Stenosis, in general, refers to any condition in which a blood vessel -- such as an artery -- or other tubular organ becomes abnormally narrow. In the context of stroke, “stenosis” is usually caused by atherosclerosis, a condition where a blood vessel supplying blood to the brain is narrowed due to fatty deposits, known as plaques, on the vessel’s inside wall. Risk factors for this type of stenosis include high blood pressure and high cholesterol.
How does stenosis contribute to stroke?
Atherosclerosis can activate cells involved in blood clotting. As clots form, they can obstruct narrowed blood vessels in the neck (the carotid artery) or the small blood vessels of the brain (intracranial arteries). Additionally, a clot or piece of the plaque can break free and flow to the brain and block an artery.
How is stenosis treated?
Several factors influence how stenosis can be treated, including the percentage of blood vessel blockage and the patient’s overall risk of a first or second stroke. Another especially important factor is the location of the stenosis, as treatment of stenosis inside the small, twisting arteries that reach deep inside the brain presents a more difficult challenge than treatment of stenosis in the large, carotid arteries in the neck.
NINDS supports many clinical trials to examine the best practices for preventing and treating stroke. Medication and lifestyle changes can be used to manage stenosis. In some cases surgery is recommended. Surgical procedures include:
Carotid endarterectomy is an option for treatment when stenosis occurs in one or both of the carotid arteries, the large arteries in the neck that supply blood to the brain.
Two large clinical trials evaluated the efficacy of carotid endarterectomy: the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS). NASCET evaluated the risks and benefits of carotid endarterectomy for individuals who experienced a stroke or other symptoms due to the stenosis such as a mini stroke or transient ischemic attack (TIA). When performed by a qualified and experienced surgeon, carotid endarterectomy is a very effective stroke prevention therapy for patients with carotid stenosis-related symptoms and greater than 70 percent stenosis in the carotid arteries. ACAS evaluated indivduals with asymptomatic stenosis, where a patient had no symptoms but the arterial blockage was identified in a medical exam. These individuals have a low annual risk of stroke, about 2 to 3 percent per year, and carotid endarterectomy cut this risk in half. In follow-up studies of otherwise healthy individuals five years post-surgery, the decreased annual stroke risk outweighed the risks of the carotid endarterectomy.
Another surgical procedure used to treat stenosis in the carotid arteries is stenting. A stent is a device, commonly made of mesh-like material, which is placed into a neck or brain blood vessel using a long, thin catheter tube threaded in through another part of the body, such as the leg. Stents support the narrowed blood vessel and hold it open to enable blood flow to the brain.
The Carotid Revascularization Endarterectomy vs. Stenting Trial (CREST) compared the efficacy of carotid endarterectomy to carotid artery stenting and found that these two surgical procedures are effective in preventing future strokes. For more details about this trial, visit the CREST Fact Sheet.
Another NINDS-supported study addressed the use of stents to treat stenosis in the arteries inside the brain. Researchers examined patients who were at high risk for a second stroke, and assessed whether the placement of an intracranial stent provided an additional benefit to an aggressive medical regimen that included blood-thinning medications and lifestyle modifications. The study, Stenting vs. Aggressive Medical Management for Preventing Recurrent Stroke in Intracranial Stenosis (SAMMPRIS) showed that, in these high risk patients, the group who participated in the medical regimen alone had better outcomes than those receiving brain stents.
For more information about stroke, visit the Know Stroke website at http://www.stroke.nih.gov.
NINDS health-related material is provided for information purposes only and does not necessarily represent endorsement by or an official position of the National Institute of Neurological Disorders and Stroke or any other Federal agency. Advice on the treatment or care of an individual patient should be obtained through consultation with a physician who has examined that patient or is familiar with that patient's medical history.
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Last Modified October 9, 2015