Ischemic Stroke
Ischemic strokes account for nearly 80 percent of all strokes. Ischemic strokes include thrombotic strokes and embolic strokes.

Thrombotic Stroke
Thrombotic strokes are caused by a blood clot that forms in a narrowed artery. Blood clots usually form in larger arteries. Thrombotic strokes account for about 2 percent of all strokes.

Blood clots may also develop in very small arteries. These are called lacunar strokes. Lacunar strokes cause tiny strokes in the brain. They are most common in people with high blood pressure.

Embolic Stroke
Emboli are abnormal pieces of material that move through the bloodstream.

An embolus may be a blood clot or a small fragment of tissue that breaks away from the wall of a diseased artery. Embolic strokes represent about 10 to 15 percent of all strokes.

Emboli move (embolize) from a location outside the brain, such as the heart or a carotid artery. They travel through the blood stream and eventually become lodged in a brain artery, which blocks blood flow and causes a stroke.

Sometimes a small clot will block the flow of blood for a short time, and then dissolve. This causes stroke symptoms that disappear within 24 hours. It is called a transient ischemic attack (TIA or 'mini stroke').

An embolus may arise from:

• A narrowed carotid artery in the neck
• Artificial heart valves
• Artificial pacemaker
• Cardiac arrhythmias:
• Such as atrial fibrillation
• Dissecting thoracic aneurysm
• Endocarditis
• Heart attack