Approximately 80% of strokes, or brain attacks, are ischemic. They can develop in major blood vessels on the surface of the brain (called large-vessel infarcts) or in small blood vessels deep in the brain (called small-vessel infarcts). Types of ischemic stroke include embolic infarct, thrombotic infarct, and lacunar infarct. Infarct of undetermined cause accounts for approximately 30% of cases of ischemic stroke.
Tissue death caused by lack of blood (embolic infarct) occurs suddenly when a blood clot (embolism) forms in one part of the body, travels through the bloodstream, and lodges in and obstructs a blood vessel in the brain. Cardiac embolism, in which a blood clot forms in the heart, accounts for about 20-30% of ischemic strokes.
Thrombotic infarct (approx. 10-15% of cases) occurs when a blood clot forms in an artery that supplies the brain, causing tissue death. This type usually occurs as a result of plaque build-up in arteries (atherosclerosis ) and develops over time.
Lacunar infarct (approx. 20% of cases) usually occurs as a result of arterial blockage caused by high blood pressure (hypertension). This type of stroke has the best prognosis.
A transient ischemic attack (TIA) is a transient event that is a risk factor for ischemic stroke. In a TIA, arterial blockage in the brain occurs briefly and resolves on its own, without causing tissue death. Approximately 10% of ischemic strokes are preceded by a TIA, and about 40% of patients who experience a TIA will have a stroke.
Hemorrhagic stroke occurs when a blood vessel in the brain ruptures and bleeds into surrounding tissue. The bleeding compresses nearby blood vessels and deprives surrounding tissue of oxygen, causing stroke. Hemorrhagic stroke usually affects a large area of the brain, is severe, and carries a high risk for death.
Intracranial hemorrhages occur when blood vessels located between the brain and the skull rupture. They can result from traumatic brain injury (TBI) or develop spontaneously as the result of a blood vessel defect or weakness such as a bulge in an artery (aneurysm) or arteriovenous malformation (AVM).
Blood vessel defects can be present at birth (congenital; e.g., berry aneurysm, arteriovenous malformation) or acquired (e.g., atherosclerotic aneurysm). Atherosclerotic aneurysm develops when plaque build-up weakens the arterial wall.
Intracranial hemorrhage occurs in the space between the brain and the skull, or cranium. Three membranes-the dura, arachnoid, and pia-surround the brain and spinal cord.
Epidural hematoma (i.e., a collection of blood) develops in the potential space between the outer membrane (dura) and the skull.
Subdural hematoma develops in the potential space between the dura and the middle layer membrane (arachnoid). This condition may become chronic when shrinkage (atrophy) of the brain (often seen in elderly patients) allows the brain to move more freely within the skull. High velocity impact to the skull may cause acute subdural hematoma, which is often fatal.
Subarachnoid hemorrhage develops in the cerebrospinal fluid-filled space between the arachnoid and the inner membrane (pia), which contains major blood vessels. Subarachnoid hemorrhages are usually caused by a ruptured aneurysm or head injury.
Intracerebral hemorrhage occurs in blood vessels located in the cerebrum, brain stem, cerebellum, or spinal cord.
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