The different forms of stroke have different specific causes.
Ischemic strokes4
Ischemic strokes are the most common form of stroke, with around 85% of strokes being of this type. They are caused by the arteries that connect to the brain becoming blocked or narrowed, resulting in ischemia - severely reduced blood flow.
These blockages are often caused by blood clots, which can form either in the arteries connecting to the brain, or further away before being swept through the bloodstream and into narrower arteries within the brain. Clots can be caused by fatty deposits within the arteries called plaque.
Hemorrhagic strokes4,6
Hemorrhagic strokes are caused by arteries in the brain either leaking blood or bursting open. The hemorrhaged blood puts pressure on brain cells and damages them. Blood vessels can burst or spill blood in the middle of the brain or near the surface of the brain, sending blood into the space between the brain and the skull.
The ruptures can be caused by conditions such as hypertension, trauma, blood-thinning medications and aneurysms (weaknesses in blood vessel walls).
Transient ischemic attack (TIA)4,6
TIAs are different from the aforementioned kinds of stroke because the flow of blood to the brain is only disrupted temporarily for a short time. They are similar to ischemic strokes in that they are often caused by blood clots or other debris.
TIAs should be regarded as medical emergencies just like the other kinds of stroke, even if the blockage of the artery is temporary. They serve as warning signs for future strokes and indicate that there is a partially blocked artery or clot source in the heart.
According to the Centers for Disease Control and Prevention (CDC), over a third of people who experience a TIA go on to have a major stroke within a year if they have not received any treatment. Between 10-15% will have a major stroke within 3 months.