What is a Stroke?

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

Ischemic Strokes

The brain needs a steady supply of blood flow carrying oxygen and nutrients – without it, brain injury can occur within minutes. Ischemic strokes, which account for 85 percent of all strokes, result from 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) is the most common cause of damaged arteries and causes 45 percent of all ischemic strokes. High blood pressure and 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 percent 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 can affect 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 percent 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 disorders and a recent heart attack can cause such a stroke.
  • Cryptogenic (unknown cause) strokes are responsible for 30 percent of all strokes, but some are later found to be due to cardiac embolism.
  • The remaining 5 percent of ischemic strokes are caused by dissection, clotting disorders and inflammatory disorders of blood vessels.

Hemorrhagic Strokes

Hemorrhagic strokes, which account for 15 percent of all strokes, occur when a blood vessel in the brain ruptures – causing bleeding in or around the brain. The two main types are:

  • Intracerebral hemorrhage occurs when a fragile brain artery ruptures – causing bleeding into the brain tissue. The rupture is sudden and can be severe causing brain damage and swelling. The most common cause is damage to small arteries from high blood pressure and diabetes. Blood-thinning medications can also increase the risk of bleeding into the brain.
  • Subarachnoid hemorrhage results from bleeding around the brain which causes a severe “worst in my life” headache. Although this type of stroke causes only 5 percent of all strokes, it is the most severe. Most are due to a brain aneurysm which forms from a weakness in the wall of the artery.

What are the 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 a 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.

More Information

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