A stroke occurs when occurs when the blood supply to part of your brain is cut off or sharply reduced. This deprives your brain tissue of oxygen and nutrients, which can cause your brain cells to die.
A stroke may be caused by an abrupt blockage of an artery (ischemic stroke) or the leaking or bursting of a blood vessel (hemorrhagic stroke). Some people may experience only a brief pause in blood flow to part of the brain (transient ischemic attack, or TIA).
Most stroke incidents (about 85 percent of cases) are ischemic strokes. It occurs when the arteries that connect to the brain become blocked or narrowed, causing severely reduced blood flow (ischemia). The most common ischemic strokes include:
- Thrombotic stroke.A thrombotic stroke occurs when a blood clot (thrombus) develops in one of the arteries supplying blood to the brain. A clot may be caused by a repeated buildup of fatty deposits, calcium and clotting factors that lead to reduced blood flow (atherosclerosis) or other artery conditions.
- Embolic stroke.An embolic stroke occurs when a blood clot or other debris forms outside of the brain – usually in the heart or large arteries of the upper chest and neck — and is swept through your bloodstream to lodge in narrower brain arteries. This type of blood clot is called an embolus.
As you age, the arteries can naturally narrow, but certain things can dangerously accelerate the process. These include:
- high blood pressure (hypertension)
- high cholesterol levels
- an excessive alcohol intake
Hemorrhagic stroke occurs when a vessel in your brain suddenly ruptures and blood begins to leak directly into brain tissue. Brain hemorrhages can be caused by many conditions that affect your blood vessels, including the force of high blood pressure (hypertension), overtreatment with anticoagulants and weak spots in your blood vessel walls (aneurysms).
Things that increase the risk of high blood pressure include:
- being overweight or obese
- drinking excessive amounts of alcohol
- a lack of exercise
- stress, which may cause a temporary rise in blood pressure
A less common cause of hemorrhage is the rupture of an abnormal and poorly formed tangle of blood vessels (arteriovenous malformation) present at birth. There are two types of hemorrhagic strokes differentiated by where the ruptured artery is located and where the resulting blood leakage occurs as follows:
- Intracerebral hemorrhage. In an intracerebral hemorrhage, a blood vessel in the brain bursts and spills into the surrounding brain tissue, damaging brain cells. Brain cells beyond the leak are deprived of blood and also damaged.
High blood pressure (hypertension) is the most common cause of this type of stroke. Less common causes include trauma, infections, vascular malformations, use of blood-thinning medications, tumors, blood clotting deficiencies and abnormalities in cerebral blood vessels.
- Subarachnoid hemorrhage. In a subarachnoid hemorrhage, an artery on or near the surface of your brain bursts and spills into the subarachnoid space between the brain and the skull, and press on the surface of the brain instead of dispersing into the tissue. This bleeding is often signaled by a sudden, severe headache.
A subarachnoid hemorrhage is commonly caused by a cerebral aneurysm, an abnormal bulging outward in the wall of an artery, ruptures. After the hemorrhage, the blood vessels in your brain may expand and narrow erratically (vasospasm), leading to brain cell damage by further limiting blood flow.
Transient ischemic attack (TIA)
A transient ischemic attack (TIA) — also known as a ministroke — produces similar symptoms, but usually lasts only a few minutes and causes no permanent damage. TIAs result from a temporary decrease in blood supply to part of your brain.
Like an ischemic stroke, a TIA occurs when a clot or debris blocks blood flow to part of your brain. A TIA doesn’t come with lasting symptoms as the blockage is temporary.
TIAs should be regarded as medical emergencies just like the other kinds of stroke, even if the blockage of the artery is temporary. Seek emergency care even if your symptoms seem to be obvious. Having a TIA puts you at higher risk of having a full-blown stroke, causing permanent damage later. If you’ve had a TIA, it means there’s likely a partially blocked or narrowed artery leading to your brain or a clot source in the heart.
It’s not possible to tell if you’re having a stroke or a TIA just only by watching your symptoms. Up to half of people whose symptoms appear to pass actually have had a stroke leading to brain damage.