A stroke, sometimes called a “brain attack,” happens when the blood supply to a part of the brain is cut off. This prevents brain tissue from getting the oxygen and nutrients it needs. As a result, brain cells begin to die within minutes, which can lead to lasting brain damage or disability. The effects of a stroke depend on the part of the brain affected and the extent of the damage. Immediate medical attention is necessary to improve outcomes.
Ischemic Stroke
An ischemic stroke occurs when a blood vessel supplying the brain is blocked by a blood clot. This is the most common type, accounting for about 87% of all strokes. The process is similar to a heart attack, but it affects the brain.
There are two primary ways an ischemic stroke can happen, distinguished by where the blood clot originates. A thrombotic stroke is caused by a thrombus, a blood clot that forms inside an artery supplying the brain. This process is often associated with atherosclerosis, a condition where fatty deposits build up on the inner walls of blood vessels over time. These strokes can sometimes develop gradually, with symptoms appearing over hours or even days.
The second type of ischemic stroke is an embolic stroke. This occurs when an embolus, a blood clot or other particle, forms elsewhere in the body and travels through the bloodstream until it lodges in a brain artery. These clots frequently originate in the heart, often linked to atrial fibrillation, which can cause blood to pool and clot. The onset is typically sudden, as the blockage happens when the clot gets stuck.
A lacunar stroke is a subtype of thrombotic stroke. These happen when one of the small, deep arteries within the brain becomes blocked. The term “lacunar” comes from the Latin word for “hole” or “cavity,” describing the small, empty spaces left in the brain tissue after these tiny strokes heal. People with high blood pressure or diabetes are more commonly affected by this type of stroke.
Hemorrhagic Stroke
A hemorrhagic stroke is caused by a blood vessel in or near the brain that ruptures and bleeds. The escaped blood also accumulates and puts pressure on the surrounding brain tissue, causing additional damage. While less common than ischemic strokes, making up about 13% of cases, they can be particularly severe.
One main type of hemorrhagic stroke is an intracerebral hemorrhage. This is bleeding from a vessel within the brain tissue. The most common cause of this type of rupture is uncontrolled high blood pressure, which weakens artery walls over time, making them susceptible to breaking. The bleeding can spread, damaging a larger area of the brain and disrupting its functions.
Another type is a subarachnoid hemorrhage. This involves bleeding into the subarachnoid space, which is the area between the brain and the thin membranes that cover it. A common cause is a ruptured saccular aneurysm, a small bulge on an artery that bursts. The sudden onset of a severe headache is a characteristic symptom of this event.
Transient Ischemic Attack
A transient ischemic attack (TIA), often referred to as a “mini-stroke,” is caused by a temporary clot that briefly blocks blood flow to the brain. The blockage resolves on its own and blood flow is restored. Because the interruption is brief, a TIA does not cause permanent brain damage. The symptoms are identical to those of a stroke but are short-lived, typically lasting only a few minutes up to 24 hours.
Despite their temporary nature, TIAs are warning signs. A TIA indicates a higher risk of a major stroke in the near future. It signals an underlying problem, such as a partially blocked artery or a condition that produces blood clots, that could lead to a permanent blockage. A TIA should be treated as a medical emergency to identify the cause and prevent a future stroke.
Classification by Cause or Location
Strokes are sometimes categorized in ways that go beyond the initial ischemic and hemorrhagic division. When diagnostic tests fail to determine a cause, it is classified as a cryptogenic stroke. This means the cause is unknown, even after a thorough investigation.
Another classification is based on the stroke’s location in the brain. For example, a stroke may be identified as affecting the brain stem, the cerebellum, or either the right or left cerebral hemisphere. This is important as the location determines which bodily functions are impacted. A stroke in the brain stem, for instance, can affect functions on both sides of the body.