What causes a stroke

Overview

A stroke occurs when blood flow to the brain is suddenly interrupted, either by a blockage or bleeding. Within minutes, brain cells begin to die from lack of oxygen, potentially causing permanent damage or death. There are two main types: ischemic strokes, accounting for about 87% of all strokes, caused by blood clots blocking arteries; and hemorrhagic strokes, about 13% of cases, caused by bleeding from ruptured blood vessels. Understanding the causes helps with both prevention and rapid treatment.

Ischemic Stroke: Blood Clots

The most common type of stroke occurs when a blood clot blocks an artery carrying blood to the brain. Clots typically form in arteries narrowed by atherosclerosis (plaque buildup). In thrombotic strokes, the clot forms in a brain artery. In embolic strokes, a clot forms elsewhere (often the heart) and travels through the bloodstream to lodge in a brain artery. Atrial fibrillation, an irregular heart rhythm, is a major cause of embolic strokes because the irregular heartbeat allows blood to pool and clot formation.

Hemorrhagic Stroke: Bleeding

Hemorrhagic strokes occur when a blood vessel ruptures and bleeds into the brain. Two main types exist: intracerebral hemorrhage, where bleeding occurs within brain tissue, usually from chronic high blood pressure damaging small vessels; and subarachnoid hemorrhage, where bleeding occurs in the space between the brain and skull, often from rupturing aneurysms. The bleeding increases pressure on the brain, damaging neurons and reducing oxygen delivery.

Major Risk Factors

Several conditions significantly increase stroke risk:

• High blood pressure (hypertension) - the leading modifiable risk factor
• Atrial fibrillation - increases risk 4-5 times
• Atherosclerosis - plaque narrows arteries over time
• Diabetes - damages blood vessels and increases clotting
• High cholesterol - contributes to plaque formation
• Smoking - damages blood vessels and increases clotting
• Obesity - associated with multiple stroke risk factors
• Physical inactivity - increases cardiovascular disease risk

Contributing Factors

Additional factors that increase stroke risk include previous strokes or TIAs (transient ischemic attacks), family history of stroke, age over 65, and certain medications like hormone replacement therapy. Migraines with aura may increase risk, as can certain blood clotting disorders. Understanding individual risk factors allows for targeted prevention strategies through medication, lifestyle changes, and medical management.