How a Stroke Happens: Brain Attacks, Causes, and Warning Signs

What Is a Stroke?

A stroke occurs when blood supply to a part of the brain is suddenly interrupted, depriving brain cells of the oxygen and glucose they need to function. Within minutes, brain cells begin to die. Stroke is the world's second leading cause of death and the leading cause of long-term disability in adults.

Strokes are sometimes called "brain attacks" — a term that captures both their sudden, emergency nature and their mechanism, which parallels how heart attacks deprive heart muscle of blood.

Types of Stroke

Ischemic Stroke (87% of strokes)

Ischemic strokes occur when a blood clot blocks or narrows an artery supplying blood to the brain.

Thrombotic stroke: A clot forms within an artery in the brain itself, usually at the site of an atherosclerotic plaque (fatty buildup). The same process that causes heart attacks, but occurring in cerebral arteries.
Embolic stroke: A clot forms elsewhere in the body — commonly in the heart (especially in patients with atrial fibrillation) — and travels through the bloodstream until it lodges in a brain artery.

Hemorrhagic Stroke (13% of strokes)

Caused by a ruptured blood vessel bleeding into or around the brain.

Intracerebral hemorrhage: Bleeding directly into brain tissue, often caused by uncontrolled high blood pressure or an arteriovenous malformation (AVM).
Subarachnoid hemorrhage: Bleeding into the space between the brain and its protective covering, most often caused by a ruptured aneurysm. Often described by patients as "the worst headache of my life."

Transient Ischemic Attack (TIA)

A TIA, often called a mini-stroke, produces stroke-like symptoms that resolve completely within 24 hours (usually within minutes). It is caused by a temporary blockage and causes no permanent damage — but it is a critical warning sign. Up to 10–15% of TIA patients will have a full stroke within 3 months, with the highest risk in the first 48 hours.

Risk Factors

Stroke risk factors divide into modifiable and non-modifiable:

Modifiable Risk Factors

High blood pressure (hypertension): The single most important modifiable risk factor for both ischemic and hemorrhagic stroke.
Atrial fibrillation: An irregular heart rhythm that causes clots to form in the heart.
Smoking: Doubles stroke risk by accelerating atherosclerosis and increasing clot formation.
Diabetes: Accelerates blood vessel damage throughout the body including the brain.
High cholesterol: Contributes to atherosclerotic plaque buildup in arteries.
Obesity and physical inactivity
Excessive alcohol consumption

Non-Modifiable Risk Factors

Age: Risk doubles approximately every decade after age 55.
Family history and genetics
Prior stroke or TIA
Race: Black Americans have nearly twice the risk of first stroke compared to white Americans.

Recognizing a Stroke: FAST

Every second counts when a stroke is occurring — the sooner treatment begins, the less brain damage results. The acronym FAST helps people recognize stroke symptoms:

F — Face drooping: One side of the face droops or is numb. Ask the person to smile — is the smile uneven?
A — Arm weakness: One arm is weak or numb. Ask the person to raise both arms — does one drift downward?
S — Speech difficulty: Slurred speech, inability to speak, or difficulty understanding speech.
T — Time to call 911: Call emergency services immediately if you observe any of these signs.

Other symptoms include sudden severe headache, sudden vision loss in one or both eyes, sudden dizziness or loss of balance, and sudden confusion.

Treatment

Ischemic Stroke

The primary treatment is restoring blood flow as quickly as possible:

tPA (tissue plasminogen activator): A clot-dissolving drug (thrombolytic) that must be given intravenously within 4.5 hours of symptom onset. Significantly improves outcomes when given promptly.
Mechanical thrombectomy: A catheter-based procedure in which the clot is physically retrieved from the blocked artery. Effective up to 24 hours after symptom onset in selected patients. Has revolutionized outcomes for large vessel occlusion strokes.

Hemorrhagic Stroke

Treatment focuses on stopping the bleeding and reducing brain pressure. Surgical options include clipping or coiling of a ruptured aneurysm. Blood pressure management is critical.

Recovery and Rehabilitation

Stroke recovery is highly variable. The brain has remarkable plasticity — the ability to rewire itself after injury — and significant recovery can occur over months to years. Rehabilitation typically involves physical therapy, occupational therapy, and speech-language therapy. Starting rehabilitation early (within 24–48 hours of stabilization) improves outcomes.

About 25% of stroke survivors recover fully. Many others make significant but incomplete recovery. Preventing a second stroke — through medication, lifestyle change, and management of underlying conditions — is a critical focus of post-stroke care.