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Rates for all Types of Stroke
Strokes may be classified into
two general types: ischemic and hemorrhagic.
Approximately 80% of strokes are
ischemic (Mohr JP, Caplan LR, Melski JW, et al. The
Harvard Cooperative Stroke Registry: a prospective registry.
Neurology. 1978; 28:754-762.). About 50% of strokes
are caused by cerebral thrombosis (formation of a blood clot
within cerebral arteries damaged by atherosclerosis), which
falls into two subcategories: large-vessel thrombosis and
small-vessel thrombosis. Large-vessel thrombosis (e.g.,
carotid, middle cerebral, or basilar arteries) accounts for
approximately 30% of strokes, while approximately 20% involve
small, deeply penetrating arteries (e.g., lenticulostriate,
basilar penetrating, medullary) that cause a type of thrombotic
stroke known as lacunar stroke.
Approximately 30% of strokes are
caused by cerebral embolism, a type of ischemic stroke that
occurs when circulation to a portion of the brains is blocked
by an embolus (clot) originating elsewhere in the circulation,
most frequently from the heart or from the cervical portion
of the carotid artery. Part or all of the embolus is
carried through the bloodstream until it lodges within an
artery too small to allow passage, preventing the blood behind
it from passing as well. Embolic strokes, which
are more common in younger patients, develop rapidly,
with maximum deficit usually present within seconds to minutes.
Hemorrhagic stroke, which accounts
for approximately 20% of all strokes, may be due to intracerebral
hemorrhage or subarachnoid hemorrhage. An intracerebral
hemorrhage (also called a parenchymal hemorrhage) occurs when
a diseased artery within the brain ruptures, flooding the
surrounding brain tissue with blood. The major risk
factor for intracerebral hemorrhage is hypertension.
Most signs and symptoms associated with intracerebral hemorrhage
are caused by the compression of brain structures and blood
vessels.
Subarachnoid hemorrhage (bleeding
into the skull or cranium that occurs when a blood vessel
on the surface of the brain ruptures and bleeds into the meninges)
usually follows the rupture of an aneurysm or an arteriovenous
malformation.
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Stroke Education
