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Approximately one-third of all strokes are preceded by one or more “mini strokes,” known as transient ischemic attacks. TIAs can occur days, weeks or even months before a stroke. TIAs are caused by temporary interruptions in the blood supply to the brain. The symptoms, which can include a sudden loss of vision or weakness in the face, arm or leg, occur rapidly and last a relatively short time, usually from a few minutes to several hours, with complete recovery within 24 hours. TIAs must be taken very seriously since they may signal that a person is at risk for a more enduring stroke, even within the next few days.
Ischemic stroke is caused by insufficient blood supply to the brain due to a blocked artery. The blockage can be caused by a blood clot traveling from the heart (embolic stroke) or from a narrowing and blockage of an artery within the brain due to atherosclerosis (thrombotic stroke).
Thrombotic stroke, also called cerebral thrombosis, is the most common type of stroke. A blood clot (thrombus) forms inside an artery in the brain, blocking blood flow. Sometimes, the clot occurs in one of the neck arteries that transport blood from the heart to the brain.
Embolic stroke (or cerebral embolism) is also caused by a blood clot. However, unlike thrombotic stroke, the clot originates somewhere other than the brain. Embolic stroke occurs when a piece of the clot (an embolus) breaks loose and is carried by the blood stream to the brain. The clot reaches a point where it can go no further and plugs the vessel, cutting off the blood supply. This sudden blockage is called an embolism.
A hemorrhagic stroke occurs when a blood vessel in or around the brain ruptures, spilling blood into the brain or the area surrounding the brain. When this occurs, the cells nourished by the artery fail to get their normal
supply of nutrients and cease to function properly. In addition, the accumulated blood from the ruptured artery soon clots, displacing normal brain tissue and disrupting brain function. The main type of hemorrhagic stroke is intracerebral hemorrhage. Intracerebral hemorrhage is caused when a defective artery within the brain bursts, flooding the surrounding brain tissue with blood. This is most often due to chronic high blood pressure.
A hemorrhagic stroke may be caused by the bursting of an aneurysm, an abnormal “bulging” of a blood vessel in the brain, or an arteriovenous malformation (AVM), a cluster of abnormal blood vessels. In the case of an aneurysm, the weak spot in the vessel wall can be stretched over the years, often by high blood pressure, which ultimately causes it to rupture. While aneurysms may not cause any symptoms until they burst, AVMs may have many symptoms, including seizures, progressive neurologic problems and severe headaches that are unresponsive to even strong medications.
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