A brain stroke occurs when a part of the brain is deprived of oxygen. This results in the death of brain cells, which can result in a variety of impairments in motor function, speech, and reasoning. There are a number of possible causes for brain strokes, and these vary depending on the type of stroke being considered.
Narrowing of the Blood Vessels
A major cause of brain strokes is the blockage of a blood vessel that brings blood from the heart to the brain, called an artery. The blood carried by the artery contains the oxygen needed for proper functioning, and a blockage that is massive enough to disrupt blood flow can therefore result in oxygen deprivation. Blockage usually results from a narrowing of the arteries in the brain that can be caused by high blood pressure, high cholesterol, diabetes, or smoking.
Embolic Stroke
Embolic strokes are also caused by a blockage that occurs within the arteries of the brain; however, this is caused by a foreign body mass becoming lodged in an artery rather than a narrowing of the artery itself. The foreign mass is typically either calcium and cholesterol deposits that line the muscles of the heart and then break free and travel through the arterial system. This is typically called a blood clot. The most common risk factor for this type of stroke is high cholesterol, which leads to an excess of deposits, greatly increasing the chance that some will break free. Calcium deposits may also break off following trauma or damage to the heart, caused by a heart attack or surgery. Other causes can be fat entering the arteries after a bone is broken somewhere in the body, infection of the arteries by bacteria or virus, or cancer of the blood that results in increased blood cells that can clog the artery.
Cerebral hemorrhage
A cerebral hemorrhage, or the bursting of a blood vessel in the brain, can lead to stroke. After the vessel disrupts, the brain will bleed, meaning that areas of brain cells may become deprived of blood or oxygen. The accumulation of blood also leads to swelling of the brain, and its expansion then causes pressure to be exerted upon the brain by the skull, further increasing damage. Risk factors for cerebral hemorrhage include head injury, abnormalities in the blood vessels of the brain that are present at birth, hypertension, and thickening of the blood vessel walls due to age.
Subarachnoid hemorrhage
A subarachnoid hemorrhage is bleeding caused by a burst blood vessel that results in a build up of blood between the layers of the arachnoid membrane that protects the gray matter, which surrounds the brain. The bleeding affects the brain in a manner similar to cerebral hemorrhages, depriving cells of oxygen and creating pressure. Subarachnoid hemorrhages are typically caused by an aneurysm, which is a weakening of a blood vessel's wall that can cause it to burst. There appears to be a genetic root in whether or not a person is at risk for aneurysm, though this is not yet completely understood by researchers. Inherited diseases like polycystic kidney disease, Ehlers-Danlos syndrome, Marfan Syndrome, and neurofibromatosis all increase a patient's risk of experiencing an aneurysm. Other risk factors include advanced age, smoking, high blood pressure or cholesterol, and alcohol abuse.
Vasculitis
Vasculitis is a group of diseases that causes blood vessels to become inflamed. This inflammation leads to damage of the arteries, which disrupts blood flow, causing a stroke. As vasculitis is a very rare disease, it is not a common cause of strokes, but for a patient experiencing vasculitis, stroke is a very likely consequence. Many of the diseases which cause vasculitis have undetermined causes, but of those that are fully understood, a list of risk factors for developing vasculitis can be created. This list includes hepatitis B, abuse of amphetamines or cocaine, lymphoma and myeloma cancers, rheumatoid arthritis, and lupus.
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