Sometimes referred to as a cerebrovascular accident (CVA), a stroke occurs in the event of oxygen deprivation to brain cells. According to the American Heart Association (AHA), the lack of oxygen to nerve cells within the affected area of the brain causes those cells to die within 3 to 4 minutes. Because brain cells do not regenerate, a severe stroke causes permanent damage, leading to loss of function in body parts controlled by the impaired nerve cells. Two major types of stroke are ischemic and hemorrhagic.
Thrombus
Ischemic strokes occur due to complete obstruction of a blood vessel within the brain. A blood clot, also referred to as thrombus, or build-up of plaque are responsible for the blockage. Atherosclerosis is a condition in which cholesterol and fat deposits form a hard substance (plaque) at a damaged area in the blood vessel lining. The AHA states that areas of arteries with atherosclerosis are common sites for thrombus formation. The American Stroke Association accounts 87 percent of all strokes to be of ischemic causes. Incomplete blockage can cause a transient ischemic attack (TIA), another type of stroke. Though TIAs do not result in permanent damage to brain cells, they provide a stern warning and a reason to seek immediate medical attention.
Embolus
When pieces of plaque or a blood clot formed in another area of the body dislodge and travel away in the bloodstream from their site of origin, a thrombus transforms into an embolus. A cerebral embolism, an embolus blocking a blood vessel in the brain, also causes an ischemic type of stroke. A heart disorder called atrial fibrillation forms emboli that often end up circulating towards the brain. The AHA also attribute this heart problem to be the cause of 15 to 20 percent of all strokes.
Hemorrhage
Hemorrhagic strokes occur as a result of ruptured blood vessels spilling into the brain. The accumulation of blood puts pressure on surrounding brain cells, cutting off circulation as well as depriving oxygen to the cells beyond the ruptured area. According to the American Stroke Association, 13 percent of all strokes are of this nature. A stroke can happen by subarachnoid hemorrhage or intracerebral hemorrhage. These subtypes differ by location: subarachnoid bleeds are between the brain and the skull, while intracerebral means bleeding within the brain. The Mayo Clinic lists uncontrolled high blood pressure and aneurysms as common conditions leading to rupture of a blood vessel.
