What Is It?

A stroke is an illness that suddenly disrupts the brain's function by injuring brain cells, usually by interfering with part of it’s the brain’s blood supply. Since the brain's blood supply can be disrupted for different reasons, doctors generally classify strokes into three categories, depending on their cause. These categories are:

• Hemorrhagic stroke - This type of stroke is caused by bleeding (hemorrhage). Bleeding can occur within the brain, or between the brain and the skull. A stroke that occurs within the brain is called an intracerebral hemorrhage, and it often is linked to hypertension (high blood pressure), old age, heavy alcohol use, or use of cocaine, or methamphetamine. A stroke that occurs between the brain and the skull is called a subarachnoid hemorrhage. As a group, hemorrhagic strokes account for about 10% to 15% of all cases of stroke.

• Thrombotic stroke - In this type of stroke, a blood clot (thrombosis) forms inside one of the brain's arteries and blocks blood flow. This usually happens inside an artery that already has been narrowed by atherosclerosis, a condition in which fatty deposits (plaques) build up along the walls of blood vessels. Thrombotic strokes are the most common type of stroke, accounting for almost 40% to 50% of cases.

• Embolic strokes - In this type of stroke, a blood clot or other solid mass of debris forms in some part of the body outside the brain, breaks loose, and travels to the brain, where it blocks a brain artery. A floating blood clot, called an embolus, often originates inside the heart as a result of sluggish blood flow caused by atrial fibrillation (a type of irregular heart rhythm) or severe heart failure. In one type of embolic stroke, the blocking debris is not a blood clot but is formed from bacteria and inflammatory cells. This type of embolus can form in the bloodstream if there is a bacterial infection on the valves of the heart, known as endocarditis. Embolic strokes account for about 20% of all stroke cases.