A stroke is a medical condition in which blood flow to a part of the brain is reduced or blocked causing cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functioning properly.
Signs and symptoms of a stroke may include facial drooping, inability to walk, move or feel on one side of the body, problems understanding or speaking, dizziness, or loss of vision to one side. Signs and symptoms often appear soon after the stroke has occurred. If symptoms last less than 24 hours, the stroke is a transient ischemic attack (TIA), also called a mini-stroke. A hemorrhagic stroke may also be associated with a severe headache. The symptoms of a stroke can be permanent. Long-term complications may include pneumonia and loss of bladder control.
The biggest risk factor for a stroke is high blood pressure. Other risk factors include high cholesterol, smoking, obesity, diabetes, a previous TIA, atrial fibrillation and air pollution. An ischemic stroke is typically caused by blockage of a blood vessel, though there are also less common causes. A hemorrhagic stroke is caused by either bleeding directly into the brain or into the space between the brain's membranes. Bleeding may occur due to a ruptured brain aneurysm. Diagnosis is typically based on a physical exam and supported by medical imaging such as a CT scan or MRI scan. A CT scan can rule out bleeding, but may not necessarily rule out ischemia, which early on typically does not show up on a CT scan. Low blood sugar may cause similar symptoms.
Prevention includes decreasing risk factors, surgery to open up the arteries to the brain in those with problematic carotid narrowing, and anticoagulant medication in people with atrial fibrillation. Aspirin or statins may be recommended by physicians for prevention. A stroke is a medical emergency. Ischemic strokes, if detected within three to four-and-a-half hours, may be treatable with medication that can break down the clot, while hemorrhagic strokes sometimes benefit from surgery. Treatment to attempt recovery of lost function is called stroke rehabilitation, and ideally takes place in a stroke unit; however, these are not available in much of the world.
In 2023, 13.2 million people worldwide had a stroke. Strokes were the second biggest cause of death. Some 105 million people who had previously had a stroke and were still alive. About 3.2 million deaths resulted from an ischemic stroke and 3.5 million deaths from a hemorrhagic stroke. Overall, two thirds of cases of a stroke occurred in those over 65 years old.
Stroke can be classified into two major categories: ischemic and hemorrhagic. An ischemic stroke is caused by interruption of the blood supply to the brain, while a hemorrhagic stroke results from the rupture of a blood vessel or an abnormal vascular structure.
About 87% of strokes are ischemic, with the rest being hemorrhagic. Bleeding can develop inside areas of ischemia, a condition known as "hemorrhagic transformation". It is unknown how many cases of hemorrhagic stroke actually start as an ischemic stroke.
In the 1970s the World Health Organization defined a "stroke" as a "neurological deficit of cerebrovascular cause that persists beyond 24 hours or is interrupted by death within 24 hours", although the word "stroke" is centuries old. This definition was supposed to reflect the reversibility of tissue damage and was devised for the purpose, with the time frame of 24 hours being chosen arbitrarily. The 24-hour limit divides a stroke from a transient ischemic attack, which is a related syndrome of stroke symptoms that resolve completely within 24 hours. With the availability of treatments that can reduce the severity of a stroke when given early, many now prefer alternative terminology, such as "brain attack" and "acute ischemic cerebrovascular syndrome" (modeled after heart attack and acute coronary syndrome, respectively), to reflect the urgency of stroke symptoms and the need to act swiftly.
During an ischemic stroke, blood supply to part of the brain is decreased, leading to dysfunction of the brain tissue in that area. There are four reasons why this might happen:
Thrombosis (obstruction of a blood vessel by a blood clot forming locally)
Embolism (obstruction due to an embolus from elsewhere in the body),
Systemic hypoperfusion (general decrease in blood supply, e.g., in shock)
Cerebral venous sinus thrombosis.
A stroke without an obvious explanation is termed a cryptogenic stroke (idiopathic); this constitutes 30–40% of all cases of ischemic stroke.
There are classification systems for an acute ischemic stroke. The Oxford Community Stroke Project classification (OCSP, also known as the Bamford or Oxford classification) relies primarily on the initial symptoms; based on the extent of the symptoms, the stroke episode is classified as total anterior circulation infarct (TACI), partial anterior circulation infarct (PACI), lacunar infarct (LACI) or posterior circulation infarct (POCI). These four entities predict the extent of the stroke, the area of the brain that is affected, the underlying cause, and the prognosis.
The TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification is based on clinical symptoms as well as results of further investigations; on this basis, a stroke is classified as being due to
(1) thrombosis or embolism due to atherosclerosis of a large artery,
(2) an embolism originating in the heart,