A stroke is defined as the sudden onset of a neurologic deficit attributable to a vascular cause. A stroke results from lack of blood flow to an area of the brain. Without adequate blood flow, neurons (nerve cells) in the brain will begin to die. Symptoms of a stroke are variable based on the area of the brain involved; sudden weakness and numbness on one side of the body is one common symptom of stroke. If the symptoms completely resolve within 24 hours, the condition is instead termed a transient ischemic attack (TIA)(TIA knol).
Nearly 500,000 people in the United States survive a stroke yearly, but it is the third leading cause of death in the U.S. and a major cause of disability worldwide. The risk of stroke increases with age, but can affect younger individuals including children and neonates. A stroke is classified as either (1) ischemic (also termed “cerebrovascular accident” [CVA]), where an occluded blood vessel deprives an area of the brain of blood flow, or (2) hemorrhagic, where there is bleeding into the brain parenchyma itself – that is, the brain tissue(intracerebral hemorrhage knol); approximately 80 percent of strokes are ischemic in nature and these are the focus of this review.
When an area of the brain is deprived of blood flow during an ischemic stroke, a cascade of events is triggered in neurons and other cells of the brain that eventually leads to cell death. Immediately after a vascular occlusion causes a stroke, much of the brain territory deprived of blood is not irreversibly damaged and may be spared permanent injury if blood flow is restored quickly over minutes to a few hours; this strategy of urgent revascularization is the basis of most acute stroke therapies currently in use.