Stroke A stroke is the death of brain tissue from a lack of oxygenated blood. There are two main types. An ischemic stroke occurs when an artery supplying blood to the brain is blocked. The blockage may be caused by a blood clot that forms in the affected artery, or when a blood clot from another area of the body travels through the circulatory system and becomes wedged in a narrower artery feeding the brain. A hemorrhagic stroke occurs when a blood vessel to the brain ruptures, causing blood to spill out of the vessel and into the surrounding tissue or the space between the brain and the skull.

According to the American Heart Association, each year, about 700,000 Americans experience a stroke. Ischemic strokes are the most common - accounting for about 88 percent of all cases. Stroke is the leading cause of serious long-term disability in the U.S. and the third leading cause of death.

Carotid Artery Disease The carotid arteries are the two main arteries that supply blood to the brain - one on each side of the neck. The carotid arteries feed the front part of the brain, the area responsible for thinking, speech, personality, sensory perception and motor function. The back part of the brain is fed by two smaller arteries, called the vertebral arteries.

Like the arteries in the heart, the carotid arteries can become clogged with fatty deposits and plaque. A partial blockage, known as stenosis, can slow the flow of blood through the affected artery. The artery can eventually become completely blocked (a carotid artery occlusion), disrupting blood flow to the brain and causing a stroke. A stroke can also occur if a piece of carotid artery plaque breaks off, travels to another site in the brain and becomes trapped, blocking that portion of the artery.

Risk for carotid artery disease increases with age. Researchers estimate about 7 percent of men and 5 percent of women over 65 have carotid artery blockages of 50 percent or greater. Patients with a 60 percent or greater stenosis have a 2 percent risk of stroke/year. Those with a 70 percent or greater degree of blockage have a 26 percent risk of having a stroke within two years and 13 percent risk of dying.

Patients with carotid artery disease may not have any symptoms of a problem until a major stroke occurs. However, some people experience "warning signs" of a stroke - minor temporary symptoms called transient ischemic attacks (TIAs). Some symptoms associated with a TIA include a sudden loss of vision in one or both eyes, sudden weakness or numbness on one side of the body, loss of movement in an arm or leg, slurring of speech or problems understanding speech, difficulties with swallowing, loss of coordination, confusion or dizziness.

Treating Carotid Artery Disease Minor degrees of carotid artery stenosis can often be treated with lifestyle modifications and medications. The treatments help reduce or slow progression of the plaque build-up, hopefully preventing a stroke. Patients may be advised to keep cholesterol, blood pressure and other medical conditions (like diabetes) under control. A low-fat diet, weight loss, regular exercise and smoking cessation are also important steps. Medications to reduce blood clots may be needed.

When carotid artery narrowing is more significant, doctors may recommend surgical intervention. The standard procedure for carotid artery disease is a carotid endarterectomy. An incision is made into the neck to access the affected area of the carotid artery. The vessel is opened and the plaque is removed. Then the artery is sewn shut to restore blood flow to the brain. More than 134,000 endarterectomies are performed each year in the U.S. For patients with stenosis of 70 percent or greater, an endarterectomy reduces the risk of stroke or death by 70 to 80 percent.

The Carotid Occlusion Surgery Study (COSS) Some people with carotid artery disease develop a natural fix for the problem. As blood flow through the diseased carotid artery decreases, tiny blood vessels around the area increase in size, allowing the blood to flow through the enlarged vessels and bypass the blockage. This process is called collateral circulation. If a patient's body produces enough collateral circulation, symptoms may not develop - even if the carotid artery is completely blocked.

Unfortunately, not everyone develops effective collateral circulation. Those who don't are at high risk for a future stroke (up to a 50 percent risk within two years). Researchers around the country are now undertaking a trial to find out if a brain bypass surgery may help reduce the risk of stroke in high-risk patients with symptoms of carotid artery occlusion. The procedure is called an "Extracranial-Intracranial Bypass" and the trial is the Carotid Occlusion Surgery Study.

To perform the bypass surgery, a small hole is drilled into the skull. Then a scalp artery is connected to a brain artery inside the skull. The procedure provides a new source of blood flow to the brain.

In a previous study, researchers found no benefit from the Extracranial-Intracranial Bypass. However, at the time, doctors didn't have any way to determine which patients might benefit the most from the surgery. Now, physicians can use PET (positron emission tomography) scans to gain images of blood flow and use of oxygen by the brain. Patients with impaired brain circulation, as determined by the PET scan, are five to ten times more likely to experience a stroke and most likely to benefit from the brain bypass surgery.

The current study aims to find out if blocked carotid arteries (and impaired brain circulation) are better treated with Extracranial-Intracranial Bypass or with standard medical treatment. Half the participants will receive the bypass surgery and half will receive standard treatment. All patients will be seen one month after the initial treatment and every three months thereafter for the next two to six years.

The Carotid Occlusion Surgery Study is going on at more than 40 sites across the country. For more information, or to find a nearby site, log on to the study's website at http://dmchost.public-health.uiowa.edu/coss/. The following institutions are taking place in the study:

Carotid Occlusion Surgery Study (COSS) sites: St. Joseph's Hospital and Medical Center/Barrow Neurological Institute, Phoenix, AZ University of Arkansas Medical Center and Central Arkansas Veterans Hospital, Little Rock, AR West Los Angeles Veterans Administration, Los Angeles, CA University of California Los Angeles Stroke Center, Los Angeles, CA Neurologic Consultants Group, INC, Mercy General Hospital, Sacramento, CA University of California San Francisco, San Francisco, CA Stanford University Stanford, CA Yale University, New Haven, CT Emory University, Atlanta, GA Loyola University, Chicago, IL Northwestern University, Chicago, IL University of Illinois, Chicago, IL Fort Wayne Neurological Center, Fort Wayne, IN Indiana University, Indianapolis, IN Indianapolis Neurosurgical Group, Indianapolis, IN University of Iowa, Iowa City, IA Massachusetts General Hospital, Boston, MA University of Michigan, Ann Arbor, MI Wayne State/Harper University Hospital, Detroit, MI Michigan State University, East Lansing, MI Park Nicollet Institute, Minneapolis, MN Mayo Clinic, Rochester, MN St. Francis Medical Center, Cape Girardeau, MO Boone Hospital Center, Columbia, MO Washington University School of Medicine, St. Louis, MO Institute for Neurosciences, Washoe Health Systems, Reno, NV JFK Medical Center, Edison, NJ Jacobs Neurological Institute, Buffalo, NY (SUNY) Columbia-Presbyterian Medical Center, New York, NY Duke University, Durham, NC Wake-Forest University, Winston-Salem, NC NeuroCareCenter, INC, Canton, OH University of Cincinnati, Cincinnati, OH Case Western Reserve, Cleveland, OH Cleveland Clinic Foundation, Cleveland, OH Ohio State Medical Center, Columbus, OH Lee-Regional Hospital, Johnstown, PA Thomas Jefferson University, Philadelphia, PA University of Pittsburgh, Pittsburgh, PA Semmes-Murphey Clinic, Memphis, TN UT Southwestern Medical Center at Dallas, Dallas, TX University of Texas Health Science Center, San Antonio, TX University of Washington, Seattle, WA Swedish Medical Center, Seattle Neuroscience Institute, Seattle, WA University of Wisconsin Hospitals and Clinics, Madison, WI

For information on carotid artery disease or stroke: American Heart Association, http://www.americanheart.org, or contact your local chapter National Institute of Neurological Disorders and Stroke, http://www.ninds.nih.gov