STROKES

A stroke is a life-threatening event that occurs when there is insufficient blood flow to some part of the brain.
It may be caused by blockage of an artery as a result of local blood vessel disease or by material passing to
the artery from another part of the body or brain.

Both of these events result in "ischemic" injury of the brain. Interestingly, the vascular changes in the brain that cause ischemic stroke are similar to the vascular
changes in the heart that cause heart attack.
Strokes may also occur as a result of bleeding in or around the brain, resulting in "hemorrhagic" stroke.

Regardless of the type of stroke, however, brain cells begin dying within minutes of the onset of the event.
Treatment must therefore be initiated as quickly as possible.

What is an Ischemic Stroke?

Ischemic strokes account for approximately 83 percent of all stroke events.
Most commonly, ischemic strokes occur because of blood clotting in an artery (a "thrombus") or atheromatous plaque in the wall of the artery.
As a result, the artery is narrowed, and blood flow stops.
Blood clots and certain other types of material may also break loose from a blood vessel in one part of the body and
travel to the brain, finally lodging in a vessel too small to allow its passage. This is called an "embolus", but embolic strokes are also ischemic because they result in stoppage of blood flow in the artery.

What is a Hemorrhagic Stroke?

Hemorrhagic strokes account for 15 percent of all strokes.
If bleeding occurs in the substance of the brain, it is called a cerebral hemorrhage.
Cerebral hemorrhage occurs most frequently in patients with poorly controlled high blood pressure. If bleeding occurs between the brain and skull (but not in the substance of the brain), it is termed either a "subdural hemorrhage" or a " subarachnoid hemorrhage".
Subdural hemorrhage occurs between the inside of the skull and the outer most layer of the linings of the brain known as the meninges. Such hemorrhages typically result from head injury.

Subarachnoid hemorrhage, on the other hand, occurs within the linings of the brain, and usually results from rupture of an aneurysm
(a balloon-like structure that develops on the wall of an artery) or an abnormal collection of blood vessels known
as an arteriovenous malformation. Arteriovenous malformations are developmental abnormalities in the brain present from birth.

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