Transient ischemic attack; TIA
Blood Flow Blockage. The brain receives about 25% of the body's oxygen, but it cannot store it. Brain cells require a constant supply of oxygen to stay healthy and function properly. Therefore, blood needs to be supplied continuously to the brain through two main arterial systems:
A reduction of, or disruption in, blood flow to the brain is the cause of a stroke. Blockage for even a short period of time can be disastrous and cause brain damage or even death.
A stroke is usually defined as two types:
The consequences of a stroke, the type of functions affected, and the severity, depend on where in the brain it has occurred and the extent of the damage.
Ischemic strokes are by far the more common type, causing over 80% of all strokes. Ischemia means the deficiency of oxygen in vital tissues. Ischemic strokes are caused by blood clots that are usually one of three types:
Thrombotic or Large-Artery Stroke and Atherosclerosis. The thrombotic stroke accounts for about 60% of all strokes. It usually occurs when an artery to the brain is blocked by a thrombus (blood clot) that forms as the result of atherosclerosis (commonly known as hardening of the arteries). These strokes are also sometimes referred to as large-artery strokes. The process leading to thrombotic stroke is complex and occurs over time:
Embolic Strokes and Atrial Fibrillation. An embolic stroke is usually caused by a dislodged blood clot that has traveled through the blood vessels (an embolus ) until it becomes wedged in an artery. Embolic strokes may be due to various conditions:
Lacunar Strokes. Lacunar infarcts are a series of very tiny, ischemic strokes, which cause clumsiness, weakness, and emotional variability. They make up the majority of silent brain infarctions and are probably a result of chronic high blood pressure They are actually a subtype of thrombotic stroke. They can also sometimes serve as warning signs for a major stroke.
Silent Brain Infarctions. Many elderly people have silent brain infarctions, small strokes that cause no apparent symptoms. They are detected in up to half of elderly patients who undergo imaging tests for problems other than stroke. The presence of silent infarctions indicates an increased risk for future stroke, and are often contributors to mental impairment in the elderly. Smokers and people with hypertension are at particular risk.
A transient ischemic attack (TIA) is an episode in which a person has stroke -like symptoms for less than 24 hours, usually less than 1-2 hours. Transient ischemic attacks (TIAs) are caused by tiny emboli (clots often formed of pieces of calcium and fatty plaque) that lodge in an artery to the brain. They typically break up quickly and dissolve but they do temporarily block the supply of blood to the brain.
A TIA is often considered a warning sign that a true stroke may happen in the future if something is not done to prevent it. TIA should be taken very seriously and treated as aggressively as a stroke.
About 20% of strokes occur from hemorrhage (sudden bleeding) into or around the brain. While hemorrhagic strokes are less common than ischemic strokes, they tend to be more deadly.
Hemorrhagic strokes are categorized by how and where they occur.
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