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Ischemic stroke :

Ischemic stroke Defn Epidemiology Risk factor Causes Pathogenesis Investigation Principles of Management

defn:

defn Ischemic stroke-a stroke caused by inadequate blood flow to a part of the brain. Because the brain requires a continuous supply of oxygen and other nutrients from the blood, this interruption in blood flow leads to dysfunction of the brain and death of the cells in the affected area.

Epediomology :

Epediomology

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Clinical examination should focus on the peripheral and cervical vascular system (carotid auscultation for bruits, blood pressure, and pressure comparison between arms), the heart ( dysrhythmia , murmurs), extremities (peripheral emboli), and retina [effects of hypertension and cholesterol emboli ( Hollenhorst plaques)]. A complete neurologic examination is performed to localize the site of stroke. An imaging study of the brain is nearly always indicated and is required for patients being considered for thrombolysis ; it may be combined with CT- or MRI-based angiography to interrogate the neck and intracranial vessels (see "Imaging Studies," below). A chest x-ray, electrocardiogram (ECG), urinalysis, complete blood count, erythrocyte sedimentation rate, serum electrolytes, blood urea nitrogen, creatinine , blood sugar, serologic test for syphilis, serum lipid profile, prothrombin time, and partial thromboplastin time (PTT) are often useful and should be considered in all patients. An ECG may demonstrate arrhythmias or reveal evidence of recent myocardial infarction (MI).

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CT may show no evidence of early infarction. Corresponding image seen on MRI diffusion weighted imaging (DWI) with changes in middle cerebral artery (MCA) territory (arrows). Late appearance of haemorrhage on CT (arrow). Corresponding appearance on gradient echo MRI (arrow). Subtle appearance of massive cerebellar infarction on CT (arrows). Corresponding appearance is more obvious on DWI MRI (arrows).

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Typical appearance of a lacunar infarct in the basal ganglia (arrow). Small cortical infarct (arrows). Large middle and anterior cerebral artery territory infarct with mass effect (arrows).

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Clots tend to form on a ruptured atheroma because the atheroma narrows the artery and slows blood flow through it, like a clogged pipe slows the flow of water. Slow-moving blood is more likely to clot. A large clot can block enough blood flowing through the narrowed artery that brain cells supplied by that artery die.

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An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery. Ischemic stroke usually results when an artery to the brain is blocked, often by a blood clot or a fatty deposit due to atherosclerosis. Symptoms occur suddenly and may include muscle weakness, paralysis, lost or abnormal sensation on one side of the body, difficulty speaking, confusion, problems with vision, dizziness, and loss of balance and coordination. Diagnosis is usually based on symptoms and results of a physical examination, imaging tests, and blood tests. Treatment may include drugs to break up blood clots or to make blood less likely to clot and surgery, followed by rehabilitation. About one third of people recover all or most of normal function after an ischemic stroke. Causes An ischemic stroke typically results from blockage of an artery that supplies the brain, most commonly a branch of one of the internal carotid arteries. Commonly, blockages are blood clots (thrombi) or pieces of fatty deposits ( atheromas , or plaques) due to atherosclerosis. Such blockages often occur in the following ways: By forming in and blocking an artery: An atheroma in the wall of an artery may accumulate more fatty material and become large enough to block the artery. Or a blood clot can form and block the artery when an atheroma ruptures (see Atherosclerosis: How Atherosclerosis Develops ). Clots tend to form on a ruptured atheroma because the atheroma narrows the artery and slows blood flow through it, like a clogged pipe slows the flow of water. Slow-moving blood is more likely to clot. A large clot can block enough blood flowing through the narrowed artery that brain cells supplied by that artery die. By traveling to another artery: A blood clot in the heart, a piece of an atheroma , or a blood clot in the wall of an artery can break off and travel through the bloodstream (becoming an embolus). The embolus may then lodge in an artery that supplies the brain and block blood flow there. (Embolism refers to blockage of arteries by materials that travel through the bloodstream to another part of the body.) Such blockages are more likely to occur where arteries are already narrowed by fatty deposits. Several conditions besides rupture of an atheroma can trigger or promote the formation of blood clots, increasing the risk of blockage by a blood clot, such as the following: Heart-related problems

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Heart-related problems: Blood clots may form in the heart or on a heart valve (including artificial valves). Strokes due to such blood clots are most common among people who have recently had heart surgery and people who have a heart valve disorder or an abnormal heart rhythm (arrhythmia), especially a fast, irregular heart rhythm called atrial fibrillation. Blood disorders: Some disorders, such as an excess of red blood cells ( polycythemia ), make blood thick, increasing the risk of blood clots. Some disorders, such as antiphospholipid syndrome and a high homocysteine level in the blood ( hyperhomocysteinemia ), make blood more likely to clot. Oral contraceptives: Taking oral contraceptives, particularly those with a high estrogen dose, increases the risk of blood clots. Another common cause of ischemic strokes is a lacunar infarction. In lacunar infarction, one of the small arteries deep in the brain becomes blocked by a mixture of fat and connective tissue—a blood clot is not the cause. This disorder is called lipohyalinosis and tends to occur in older people with diabetes or poorly controlled high blood pressure. Lipohyalinosis is different from atherosclerosis, but both disorders can cause blockage of arteries. Only a small part of the brain is damaged in lacunar infarction. Rarely, small pieces of fat from the marrow of a broken long bone, such as a leg bone, are released into the bloodstream. These pieces can clump together and block an artery. The resulting disorder, called fat embolism syndrome, may resemble a stroke. An ischemic stroke can also result from any disorder that reduces the amount of blood or oxygen supplied to the brain, such as severe blood loss or very low blood pressure. Occasionally, an ischemic stroke occurs when blood flow to the brain is normal but the blood does not contain enough oxygen. Disorders that reduce the oxygen content of blood include a severe deficiency of red blood cells (anemia), suffocation, and carbon monoxide poisoning. Usually, brain damage in such cases is widespread (diffuse), and coma results. An ischemic stroke can occur if inflammation of blood vessels ( vasculitis ) or infection (such as herpes simplex) narrows blood vessels that supply the brain. Migraine headaches or drugs such as cocaine and amphetamines can cause spasm of the arteries, which can narrow the arteries supplying the brain and cause a stroke. Clogs and Clots: Causes of Ischemic Stroke When an artery that carries blood to the brain becomes clogged or blocked, an ischemic stroke can occur. Arteries may be blocked by fatty deposits ( atheromas , or plaques) due to atherosclerosis. Arteries in the neck, particularly the internal carotid arteries, are a common site for atheromas . Arteries may also be blocked by a blood clot (thrombus). Blood clots may form on an atheroma in an artery. Clots may also form in the heart of people with a heart disorder. Part of a clot may break off and travel through the bloodstream (becoming an embolus). It may then block an artery that supplies blood to the brain, such as one of the cerebral arteries. Symptoms Usually, symptoms occur suddenly and are often most severe a few minutes after they start because most ischemic strokes begin suddenly, develop rapidly, and cause death of brain tissue within minutes to hours. Then, most strokes become stable, causing little or no further damage. Strokes that remain stable for 2 to 3 days are called completed strokes. Sudden blockage by an embolus is most likely to cause this kind of stroke. Less commonly, symptoms develop slowly. They result from strokes that continue to worsen for several hours to a day or two, as a steadily enlarging area of brain tissue dies. Such strokes are called evolving strokes. The progression of symptoms and damage is usually interrupted by somewhat stable periods, during which the area temporarily stops enlarging or some improvement occurs. Such strokes are usually due to the formation of clots in a narrowed artery. Many different symptoms can occur, depending on which artery is blocked and thus which part of the brain is deprived of blood and oxygen (see Brain Dysfunction: Brain Dysfunction by Location ). When the arteries that branch from the internal carotid artery (which carry blood along the front of the neck to the brain) are affected, the following are most common: Blindness in one eye Inability to see out of the same side in both eyes Abnormal sensations, weakness, or paralysis in one arm or leg or on one side of the body When the arteries that branch from the vertebral arteries (which carry blood along the back of the neck to the brain) are affected, the following are most common: Dizziness and vertigo Double vision Generalized weakness on both sides of the body Many other symptoms, such as difficulty speaking (for example, slurred speech), impaired consciousness (such as confusion), loss of coordination, and urinary incontinence, can occur. Severe strokes may lead to stupor or com

Slide 14:

Heart-related problems: Blood clots may form in the heart or on a heart valve (including artificial valves). Strokes due to such blood clots are most common among people who have recently had heart surgery and people who have a heart valve disorder or an abnormal heart rhythm (arrhythmia), especially a fast, irregular heart rhythm called atrial fibrillation. Blood disorders: Some disorders, such as an excess of red blood cells ( polycythemia ), make blood thick, increasing the risk of blood clots. Some disorders, such as antiphospholipid syndrome and a high homocysteine level in the blood ( hyperhomocysteinemia ), make blood more likely to clot. Oral contraceptives: Taking oral contraceptives, particularly those with a high estrogen dose, increases the risk of blood clots. Another common cause of ischemic strokes is a lacunar infarction. In lacunar infarction, one of the small arteries deep in the brain becomes blocked by a mixture of fat and connective tissue—a blood clot is not the cause. This disorder is called lipohyalinosis and tends to occur in older people with diabetes or poorly controlled high blood pressure. Lipohyalinosis is different from atherosclerosis, but both disorders can cause blockage of arteries. Only a small part of the brain is damaged in lacunar infarction. Rarely, small pieces of fat from the marrow of a broken long bone, such as a leg bone, are released into the bloodstream. These pieces can clump together and block an artery. The resulting disorder, called fat embolism syndrome, may resemble a stroke. An ischemic stroke can also result from any disorder that reduces the amount of blood or oxygen supplied to the brain, such as severe blood loss or very low blood pressure. Occasionally, an ischemic stroke occurs when blood flow to the brain is normal but the blood does not contain enough oxygen. Disorders that reduce the oxygen content of blood include a severe deficiency of red blood cells (anemia), suffocation, and carbon monoxide poisoning. Usually, brain damage in such cases is widespread

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during AF because blood may pool and form clots in the poorly contracting atria and especially in the left atrial appendage

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