A stroke is a serious and potentially life threatening medical condition that occurs when the flow of blood to the brain is disrupted. Blood carries oxygen to the brain, which controls all of the body's functions. Without oxygen-rich blood, the brain begins to shut down. If blood flow cannot reach the region that controls a particular body function, that part of the body will not work as it should, according to the American Stroke Association (ASA).

The most common type of stroke is ischemic stroke, which is caused by a clot obstructing the flow of blood to the brain. A stroke can also be hemorrhagic, meaning it is caused by a blood vessel rupturing and preventing blood flow to the brain. Some strokes can be caused by temporary clots. They are referred to as transient ischemic attacks or "mini strokes", according to the ASA.

Stroke is the second leading cause of both disability and death worldwide, according to a 2021 review published in the journal Neurology. Approximately 137,000 people die of stroke each year in the United States alone.

Types and causes of stroke

Ischemic stroke

Ischemic stroke occurs when fatty deposits inside blood vessel walls become loose, forming blood clots that clog the vessel and make it impossible for blood to flow through. This type of stroke accounts for about 87% of all cases, according to the ASA.

There are two kinds of obstructions, or blood clots, that can cause ischemic strokes.

Cerebral thrombosis occurs when a blood clot, or thrombus, develops in one of the brain's blood vessels, causing what is known as a thrombotic stroke. Embolic strokes, on the other hand, are caused by cerebral embolism, which is when a portion of a blood clot in another part of the body — like the heart — comes loose, travels through the bloodstream and clogs a blood vessel in the brain.

Hemorrhagic stroke

Hemorrhagic stroke occurs when a weakened vessel ruptures and bleeds into the surrounding brain. The blood accumulates and compresses the surrounding brain tissue, triggering the symptoms. This type of stroke accounts for about 13% of cases, according to the ASA.

Two types of weakened blood vessels usually cause hemorrhagic stroke: Aneurysms and arteriovenous malformations (AVMs).

An aneurysm is a weak area in a blood vessel that usually enlarges. It is often described as a "ballooning" of the blood vessel. Aneurysm usually develop at branching points of arteries and are caused by constant pressure from blood flow, according to the ASA. Arteriovenous malformation (AVM) occurs when a tangle of blood vessels in the brain bypasses normal brain tissue and directly diverts blood from the arteries to the veins.

Transient ischemic attack

Transient ischemic attack (TIA), often referred to as "mini stroke", occurs when there is a temporary blockage of blood flow to the brain, according to the ASA. The clot usually dissolves on its own or gets dislodged, and the symptoms usually last less than five minutes. While a TIA does not cause permanent damage, it is a signal that a full-blown stroke may happen in the near future.

Cryptogenic stroke

Strokes without a known cause are called cryptogenic. It is estimated that about 1 in 3 ischemic strokes are cryptogenic, according to the ASA. Possible hidden causes of stroke include irregular heartbeat, heart structure problem, hardening of the arteries or blood clotting disorders.

A number of rare heritable and non-heritable conditions should be additionally considered in the diagnosis of cryptogenic stroke, according to a 2021 review published in the Journal of Neurology. These include Fabry disease, Moyamoya angiopathy, Sneddon syndrome, Susac syndrome and Takotsubo syndrome.

Signs of stroke

Symptoms of stroke vary depending on what part of the brain is affected. But a quick way to remember the possible immediate effects of a stroke is the acronym F.A.S.T., according to the ASA.

F- Face drooping: One part of the face may be drooping or numb.

A- Arm weakness: One arm may feel weak or numb.

S- Speech difficulty: Speech may be slurred or slow

T- Time to call 911: If someone experiences these symptoms, they need medical attention immediately, even if the symptoms go away.

Dr. Bal Athwal, a consultant neurologist at HCA Healthcare in the U.K., told Live Science that while the FAST test can be used to identify the symptoms of a lot of strokes, there are some other symptoms to watch out for, all of which have a sudden onset: