Strokes or CVA's (Cerbrovascular Accidents) are medical emergency caused by the lack of blood flow proximal to the area of discontinuation in an artery in the brain. This area begins to become ischemic (dying due to lack of oxygen) and then infarct (die) if not treated.
CVA's can be caused by one of two things. The first one is an occlusion of the blood vessel, usually due to plaque buildup (Clots) in an artery that reaches a point where perfusion is not happening in sufficient amounts. Another type of stroke, which is also more dangerous is an ruptured aneurysm which are arterisnthat have dilated due to high pressures, and burst after a while, these are called hemorraghic strokes. Hemmoraghic strokes are much more dangerousnbecause not only is blood stopped from reaching the area of the brain proximalnto it, it is accompanied by severe blood loss and if not treated fast enough, lethal compression of the brain but to increased intracranial pressure.
