What Are the Causes of Strokes?

A stroke is an injury to a portion of the brain due to inadequate blood supply. There are several causes of stroke. 

The Importance of Getting Enough Blood Supply in the Brain

The most common cause of stroke is a blockage of blood flow within a blood vessel in the brain. Arteries located in the neck and in the brain supply blood to the brain to keep it functioning.

This blood delivers oxygen and nutrients necessary for the brain to create the biochemical energy it needs to function normally. 

When Blood Flow to the Brain is interrupted

When blood flow within a blood vessel is blocked, the nearby region of the brain is deprived of oxygen and vital nutrients. This is called ischemia. The immediate consequence is that the lack of blood makes it difficult for the affected region of the brain to function. If the lack of blood flow is very brief, and then restored, a reversible stroke, also called a TIA or a mini-stroke will ensue. If blood flow is not quickly restored, the injury will become more extensive- possibly permanent, resulting in a stroke.

How is Blood Flow Interrupted?

Blood Clot

Interruption of blood flow may occur due to a blood clot, called a thrombus or an embolus. This causes an ischemic stroke.


A thrombus is the partial or complete clogging of an artery due to a blood clot.


An embolus is a blood clot that initially forms in an artery, and then loosens and travels until it reaches an artery in the brain, causing blockage and damage in the brain.


Another cause of stroke is a bleeding on the brain. When a blood vessel is torn, blood leaks out, causing irritation to the nearby brain tissue.

When the blood vessel is severed and blood loss occurs, there is also inadequate blood supply to the target destination in the brain.  A stroke caused by bleeding from a leaking or torn blood vessel is a hemorrhagic stroke.


Low blood supply to the brain is a less common cause of stroke. When the fluid or blood volume in the body is exceptionally low, the brain may not receive enough blood. While there is no blood clot in this instance, the brain suffers because the areas of the brain that are normally supplied by extensions of tiny branched arteries may not receive an adequate blood supply. A stroke resulting from low blood supply is usually called a watershed stroke. Certain areas of the brain are more susceptible to a watershed stroke.

Common Causes of Stroke

Cerebral Causes of Stroke

*Cerebrovascular disease

*Aneurysm- this is an outpouching of an artery. An aneurysm may leak or rupture, causing a hemorrhage.

*AVM/ arteriovenous malformation-this is a malformed group of connected blood vessels, usually containing arteries and veins. An AVM may rupture or form a thrombus, causing a hemorrhagic or ischemic stroke. 

*Vasospasm- this is when an artery suddenly spasms, disturbing blood flow and causing ischemia even in the absence of a blood clot.

Cardiac Causes of Stroke

*Arrhythmia-abnormal rhythms and irregular heart rhythms such as untreated atrial fibrillation can promote the formation of a blood clot and cause an embolus to travel to the brain.

*Heart attack- can cause either a watershed infarct or may cause an embolus to travel to the brain.

*Carotid Artery Disease- this is disease and clotting within the blood vessels located in the neck that supplies the brain. An embolus from the carotid artery or blockage of the carotid artery can cause a stroke.

*Hypertension-this contributes to cerebrovascular disease, carotid artery disease, and heart disease.

Additionally, sudden extreme episodes of hypertension may cause vasospasm or hemorrhage of an aneurysm.

Systemic Causes of Stroke

*Hypotension- can occur due to severe blood loss or dehydration, causing hypoperfusion of the brain and watershed stroke.

*Medication- medications that affect blood clotting, bleeding or blood pressure can lead to a stroke.

*Drugs-illegal drugs such as cocaine, methamphetamine, and other powerful stimulants can cause vasospasm of any artery in the body. This can cause a heart attack, a stroke due to vasospasm of cerebral arteries, or the dislodging of a blood clot that can travel to the brain, causing a stroke.

*Blood clotting disorders- can cause an increase in blood clot formation or an increase in bleeding.

*Infection- can alter the body’s blood clotting or bleeding susceptibility, leading to a thrombus, an embolus or a hemorrhage. In rare instances, an infectious organism can actually physically block a blood vessel, causing ischemia.

*Inflammation -can contribute to increased blood clotting.

*Air embolus- is an air bubble that travels to the brain from somewhere else in the body, obstructing a blood vessel, and causing a stroke.


Weiner, William J., Goetz, Christopher G, Neurology for the Non-Neurologist, Fifth Edition, Lippincott Wiliams& Winkins, 2004

Martin Samuels and David Feske, Office Practice of Neurology,  2nd Edition, Churchill Livingston, 2003