The devastating effects of stroke are often permanent because dead brain cells aren't replaced. Cerebral thrombosis and cerebral embolism are by far the most common, accounting for about 70-80 percent of all strokes. They're caused by clots or particles that plug an artery. Cerebral and subarachnoid hemorrhages are caused by ruptured blood vessels. They have a much higher fatality rate than strokes caused by clots.
Cerebral thrombosis is the most common type of stroke.
Blood clots usually form in arteries damaged by atherosclerosis. Cerebral thrombotic strokes often occur at night or first thing in the morning, when blood pressure is low. Cerebral embolism accounts for 5 to 14 percent of all strokes. The clot is carried by the bloodstream until it lodges in an artery leading to or in the brain, blocking the flow of blood. The most common cause of these emboli is blood clots that form during atrial fibrillation, a disorder found in close to 2 million Americans.