Transient Ischemic Attack (TIA)

Pictures & Images

See all Pictures & Images

Overview, Causes, & Risk Factors

A transient ischemic attack (TIA) is caused by an interruption of blood flow to brain cells. If the symptoms resolve completely in under 24 hours, this is called a TIA or "mini stroke." If the symptoms do not resolve, the event is called a stroke.

A brief interruption to the blood flow can cause a decrease in brain function (neurologic deficit). Symptoms vary with the area of the brain affected and may include changes in vision, speech or comprehension, vertigo, decreased movement or sensation in a part of the body, or changes in the level of consciousness. If the blood flow is decreased for a sufficient period, brain cells in the area die (infarct), causing permanent damage to that area of the brain or even death.

The loss of blood circulation to the brain can be caused by the following:

• narrowing of a blood vessel
• blood clotting within an artery of the brain
• blood clot traveling to the brain from somewhere else in the body (e.g., heart)
• a blood disease, cancer, and others
• inflammation of blood vessels
• injury to blood vessels

In a TIA, the blood supply is only temporarily blocked. For example, a blood clot may dissolve and allow blood to flow normally again.

Atherosclerosis ("hardening of the arteries") is a condition where fatty deposits occur on the inner lining of the arteries, which dramatically increases the risk for both TIAs and stroke. Atherosclerotic plaque is formed when damage occurs to the lining of an artery. Platelets clump around the area of injury as a normal part of the clotting and healing process. Cholesterol and other fats also collect at this site, forming a mass within the lining of the artery. A clot (thrombus) may form at the site of the plaque, triggered by irregular blood flow in this location, and the thrombus may then block blood vessels in the brain.

Pieces of plaque or clots can also break off and travel through the bloodstream from distant locations, forming an embolus that can occlude the small arteries, causing TIAs.

About one-third of the people diagnosed with TIA will later have a stroke. However, about 80 to 90% of people who have a stroke secondary to atherosclerosis had TIA episodes before their stroke. Approximately one-third of the people with TIA will have recurrent TIAs, and one-third will have only a single episode of TIA. The age of onset varies, but incidence rises dramatically after age 50. TIA is more common among men and African-Americans.

Less common causes of TIA include blood disorders (including polycythemia, sickle cell anemia, and hyperviscosity syndromes where the blood is very thick), spasm of the small arteries in the brain, abnormalities of blood vessels caused by disorders such as fibromuscular dysplasia, inflammation of the arteries (arteritis, polyarteritis, granulomatous angiitis), systemic lupus erythematosus, and syphilis. Hypotension (low blood pressure) may precipitate symptoms in an individual with a pre-existing vascular lesion.

Other risks for TIA include high blood pressure (hypertension), heart disease, migraine headaches, smoking, diabetes mellitus, and increasing age.