Causes

There are two main causes of stroke: a blocked artery (ischemic stroke) or leaking or bursting of a blood vessel (hemorrhagic stroke). Some people may have only a temporary disruption of blood flow to the brain, known as a transient ischemic attack (TIA), that doesn't cause lasting symptoms.

Ischemic stroke

This is the most common type of stroke. It happens when the brain's blood vessels become narrowed or blocked, causing severely reduced blood flow (ischemia). Blocked or narrowed blood vessels are caused by fatty deposits that build up in blood vessels or by blood clots or other debris that travel through your bloodstream and lodge in the blood vessels in your brain.

Some initial research shows that COVID-19 infection may be a possible cause of ischemic stroke, but more study is needed.

Hemorrhagic stroke

Hemorrhagic stroke occurs when a blood vessel in your brain leaks or ruptures. Brain hemorrhages can result from many conditions that affect your blood vessels. Factors related to hemorrhagic stroke include:

• Uncontrolled high blood pressure
• Overtreatment with blood thinners (anticoagulants)
• Bulges at weak spots in your blood vessel walls (aneurysms)
• Trauma (such as a car accident)
• Protein deposits in blood vessel walls that lead to weakness in the vessel wall (cerebral amyloid angiopathy)
• Ischemic stroke leading to hemorrhage

A less common cause of bleeding in the brain is the rupture of an abnormal tangle of thin-walled blood vessels (arteriovenous malformation).

Transient ischemic attack (TIA)

A transient ischemic attack (TIA) — sometimes known as a ministroke — is a temporary period of symptoms similar to those you'd have in a stroke. A TIA doesn't cause permanent damage. They're caused by a temporary decrease in blood supply to part of your brain, which may last as little as five minutes.

Like an ischemic stroke, a TIA occurs when a clot or debris reduces or blocks blood flow to part of your nervous system.

Seek emergency care even if you think you've had a TIA because your symptoms got better. It's not possible to tell if you're having a stroke or TIA based only on your symptoms. If you've had a TIA, it means you may have a partially blocked or narrowed artery leading to your brain. Having a TIA increases your risk of having a full-blown stroke later.