Stroke

A stroke happens when blood flow to part of the brain is cut off or reduced, which kills brain cells. The two main types are ischemic strokes, caused by a lack of blood flow, and hemorrhagic strokes, caused by bleeding. In either case, the affected brain tissue stops working properly.

Common signs include a drooping face, trouble walking, weakness or numbness on one side of the body, difficulty speaking or understanding speech, dizziness, or vision loss in one eye. These symptoms usually appear quickly after the stroke occurs. If they go away within 24 hours, the event is called a transient ischemic attack (TIA), or mini-stroke. A hemorrhagic stroke may also come with a severe headache. Symptoms can become permanent. Long-term problems can include pneumonia and loss of bladder control.

The biggest risk factor is high blood pressure. Others include high cholesterol, smoking, obesity, diabetes, a previous TIA, end-stage kidney disease, and atrial fibrillation. Ischemic strokes are usually caused by a blocked blood vessel, though less common causes exist. Hemorrhagic strokes happen when bleeding occurs directly into the brain or into the space between the brain’s membranes, often from a ruptured aneurysm. Diagnosis starts with a physical exam and is confirmed with imaging like a CT scan or MRI. A CT scan can rule out bleeding but may not show early ischemia. Other tests, such as an electrocardiogram (ECG) and blood work, help identify risk factors and causes. Low blood sugar can mimic stroke symptoms.

Prevention involves lowering risk factors, surgery to open narrowed carotid arteries in the neck, and blood thinners for people with atrial fibrillation. Doctors may also recommend aspirin or statins. A stroke is a medical emergency. For ischemic strokes caught within three to four-and-a-half hours, clot-busting medication may help; hemorrhagic strokes sometimes require surgery. Recovery therapy, called stroke rehabilitation, works best in a stroke unit, but such units are not available in many parts of the world.

In 2023, 15 million people worldwide had a stroke. In 2021, strokes were the third leading cause of death, accounting for about 10% of all deaths. In 2015, roughly 42.4 million people who had survived a stroke were still alive. Between 1990 and 2010, the annual number of strokes dropped by about 10% in developed countries but rose by 10% in developing ones. In 2015, stroke was the second most common cause of death after coronary artery disease, causing 6.3 million deaths (11% of the total). Of those, about 3.0 million were from ischemic strokes and 3.3 million from hemorrhagic strokes. About half of people who have a stroke die within a year. Overall, two-thirds of strokes occur in people over 65.

Strokes are classified as ischemic or hemorrhagic. Ischemic strokes happen when blood supply to the brain is interrupted; hemorrhagic strokes result from a ruptured blood vessel or abnormal vascular structure. About 87% of strokes are ischemic, and the rest are hemorrhagic. Bleeding can sometimes develop inside an area of ischemia—called hemorrhagic transformation—and it is unknown how many hemorrhagic strokes actually start as ischemic ones.

In the 1970s, the World Health Organization defined a stroke as a neurological deficit from a cerebrovascular cause lasting more than 24 hours or ending in death within that time. The 24-hour cutoff was chosen arbitrarily to separate stroke from transient ischemic attack (TIA), where symptoms resolve fully within a day. Because early treatment can reduce stroke severity, many now prefer terms like "brain attack" or "acute ischemic cerebrovascular syndrome" to stress the urgency.

Ischemic strokes result from decreased blood supply to part of the brain. Four main causes are thrombosis (a clot forming locally), embolism (a clot traveling from elsewhere), systemic hypoperfusion (low blood flow, as in shock), and cerebral venous sinus thrombosis. About 30–40% of ischemic strokes have no clear cause and are called cryptogenic. Classification systems help predict the affected brain area, cause, and outlook. The Oxford Community Stroke Project (OCSP) system sorts strokes by initial symptoms into total anterior circulation infarct, partial anterior circulation infarct, lacunar infarct, or posterior circulation infarct. The TOAST classification uses both symptoms and further test results.