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What is a Stroke?

A stroke is a brain injury resulting from a blocked or leaking blood vessel that carries blood to the brain.


Blocked Artery Strokes – Ischemic Strokes

 The brain needs a steady supply of blood flow carrying oxygen and nutrients – without it, brain injury occurs within minutes. Strokes from blood clots, also called Ischemic strokes, account for 85 % of all strokes.  They are caused by a lack of blood flow to the brain due to blockage of a brain artery. The most common causes are:

  • Atherosclerosis: (hardening of the arteries) causes damaged arteries (45 % of all ischemic strokes). High blood pressure, cholesterol, diabetes and smoking cause injury to the lining of the artery and the wall thickens with plaque. Stroke risk is greatest when more than 70 % of the artery is blocked or when an artery plaque becomes unstable and ruptures.
  • A thrombus: is a blockage of an artery with plaque and blood clot. Atherosclerosis affects the      large carotid arteries in the neck, the medium-sized intracranial arteries at the base of the brain, or the small arteries deep inside the brain.
  • Cardiac embolism: causes 20% of all ischemic strokes. An embolus occurs when a clot forms in the heart and a piece breaks loose to block an artery within the brain. Heart conditions such as atrial fibrillation, heart failure, heart valve problems and a recent heart attack can cause such a stroke.
  • Strokes from an unknown cause are responsible for 30 %of all strokes.
  • The remaining 5 % of ischemic strokes are caused by dissection, clotting disorders and inflammatory disorders of blood vessels.


Bleeding Stroke – Hemorrhagic Stroke

15 % of all strokes occur when a blood vessel in the brain breaks open – causing bleeding in or around the brain. This is also called a hemorrhagic stroke. Two main types are:

  • Bleeding within the Brain- In this kind of stroke, a fragile brain artery breaks open, causing bleeding into the brain tissue.  Bleeding is sudden and is severe causing brain damage and swelling.  Most common cause of damage to arteries is from high blood pressure and diabetes.  Blood thinning medications also increase the risk of bleeding into the brain.
  • Bleeding outside the brain, between the brain and skull.  This kind of stroke results from bleeding around the brain which causes a severe “worst in my life” headache.  5 % of all stroke, but most severe.  Usually due to brain aneurysms which form from weakness in wall of artery.    It can also be caused by a head injury


Warning signs of a Stroke:

  • Sudden weakness or numbness of the face, arm or leg, especially on one side of the body
  • Sudden confusion, trouble speaking or understanding
  • Sudden trouble seeing in one or both eyes
  • Sudden trouble walking, dizziness, loss of balance or coordination
  • Sudden, severe headaches with no known cause


A stroke is medical emergency that must be treated right away. Even if the symptoms go away at first, some patients will go on to have a stroke, usually within hours or even days.



For more information:

Go to the Stroke health topic.