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Stroke types: hemorrhagic versus ischemic.

Hemorrhagic Strokes

About 20 percent of all strokes are hemorrhagic; this type of stroke involves the rupture of a blood vessel in or around the brain. This is most likely to happen in people with high blood pressure, which weakens vessel walls. Although every stroke is serious, hemorrhagic events are often devastating because they can occur in young people out of the blue and are more likely to cause death.

Hemorrhagic strokes may occur in either of two places. When bleeding takes place inside the brain, the stroke is called an intracerebral hemorrhage. When a vessel on the surface of the brain bursts and bleeds into the space between the brain and the skull, it is classified as a subarachnoid hemorrhage.

Intracerebral Hemorrhage

Two thirds of intracerebral hemorrhages occur in people with a history of high blood pressure. These hypertensive intracerebral hemorrhages occur deep within the brain.

These events tend to occur when people are awake and sometimes when they are under stress. Symptoms emerge relentlessly over a period of minutes, and vomiting or headache is likely. Such symptoms rarely happen in ischemic stroke. Recovery depends on the size and location of the hemorrhage.

One special category is a hypertensive cerebellar hemorrhage, in which blood leaks into the cerebellum, the brain structure that guides the coordination of movement and balance. As a result, the person experiences abrupt dizziness and loss of balance, which impede walking or standing. Prompt diagnosis of a cerebellar hemorrhage is crucial because early surgical removal of the blood can be lifesaving and may result in a good recovery.

A vascular abnormality called an arteriovenous malformation can also cause an intracerebral hemorrhage. Normally, arteries (which carry blood away from the heart) and veins (which carry blood back to the heart) are connected by very small blood vessels called capillaries. An arteriovenous malformation is a tangle of thin-walled arteries and veins that are missing these capillaries. These vessels bleed easily, which can put pressure on a part of the brain or drain blood away from a specific area.

Subarachnoid Hemorrhage

Like an intracerebral bleed, a subarachnoid event is caused by a burst blood vessel; in this case, however, the damage may be more extensive because blood accumulates between the brain and the skull and presses the surface of the brain instead of dispersing into the tissue. The surface of the brain is covered by three thin membranous layers called meninges. The outside layer adheres to the skull; the innermost adheres to the brain. Between the inner and middle layers is the subarachnoid space, which is normally filled with fluid. A subarachnoid. hemorrhage occurs when blood leaks into this space.

Most subarachnoid hemorrhages are a consequence of a burst cerebral aneurysm, a small pocket or balloon that usually develops at the junction of two blood vessels. This weakening may be due to atherosclerotic buildup, traumatic injury, or a congenital defect. A smaller percentage of subarachnoid hemorrhages result from other blood vessel malformations or a blow to the head, while some aneurysms have no detectable cause.

In about 45 percent of cases, a severe headache is the first major symptom of a subarachnoid hemorrhage. People often characterize it as the worst headache they ever had and use words such as "explode" and "burst" to describe it; about half of such people lose consciousness. Other early symptoms may include a stiff neck, nausea and vomiting, mental impairment, or seizures.

A person who has had a subarachnoid hemorrhage is immediately put to bed, usually in a quiet, dark room, in an effort to prevent additional bleeding. Aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) cannot be used to relieve head or neck pain because they increase the risk of bleeding; acetaminophen (Tylenol) or another more potent analgesic may be recommended instead.

Ischemic Strokes

About 80 percent of strokes are ischemic in origin, which means they are caused by a blockage of the vessels that supply blood to the brain. This type of event affects more than 400,000 people in the United States every year.

Atherosclerosis plays an important role in most ischemic strokes. This potentially dangerous narrowing of blood vessels, which occurs when cholesterol and other debris build up, can reduce blood flow and deprive brain cells of vital oxygen and nourishment. In most ischemic strokes, however, a blood clot finishes the job by totally obstructing the flow of blood through the vessel. When a blood clot forms somewhere else (for instance, in the heart) and then travels through the blood stream until it lodges in a blood vessel, it is called an embolus, and the result is an embolic stroke. [Editor's Note: See Issue #75.]

The three main types of ischemic strokes parallel the three types of transient ischemic attacks (TIAs).

Atherothrombotic Stroke

An atherothrombotic stroke is an ischemic event that occurs when a large artery to the brain, already narrowed by atherosclerosis, becomes completely blocked by the formation of a clot. When brain cells die as a result, this is called a cerebral infarction. Such strokes are sometimes preceded by low-flow TIAS and are similar in origin to a heart attack, but the blockage takes place in an artery leading to the brain rather than in one supplying the heart muscle.

Embolic Stroke

The "embolic stroke" generally occurs when a clot that has formed elsewhere in the body, typically in the heart of ascending part of the aorta (the main artery from the heart), breaks off and travels through the blood stream until it blocks an artery to the brain. People who have this type generally fare worse than those with atherothrombotic strokes, especially when the embolus blocks one of the major arteries located at the base of the brain. The symptoms of an embolic stroke usually appear suddenly and with great severity. They may come and go, persisting for minutes or hours and then disappearing, or the stroke may become progressively worse. The neurological damage typical of embolic strokes is similar to that of atherothrombotic strokes, depending on the location of the embolism.

Many embolic strokes are related to atrial fibrillatiom, a type of arrhythmia (irregular heart rhythm) that promotes formation of clots in the heart. People who have survived a heart attack are also at high risk for a stroke for several weeks afterward because new clots may form on the surface of damaged heart tissue, dislodge, and travel to the brain.

Lacunar Stroke

The word "lacuna" means a missing part or gap. A lacunar stroke is caused by blockage of one of the smaller blood vessels in the brain. It may be hard to identify because only a small amount of brain tissue is likely to be injured. Damage is frequently confined to the motor control areas and may manifest itself solely as a one-sided physical weakness or disability. Hypertension (high blood pressure), which damages blood vessels, is the largest single cause of lacunar strokes; as a result, long-term treatment usually focuses on lowering the blood pressure to prevent recurrent events.

Physicians must determine which type of stroke has occurred in order to choose the most appropriate treatment. People who have had a lacunar stroke are most likely to regain lost neurological functions because only a small area has been affected and other parts of the brain may take over. Damage brought on by an atherothrombotic stroke tends to worsen during the early stages because additional clots may form and travel to the brain or the original clot may enlarge and continue to block the blood supply. Embolic strokes do recur unless the source of the embolus is treated.
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Publication:Nutrition Health Review
Date:Jun 22, 1996
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