Causes of Transient Ischemic Attacks
Transient ischemic attacks involve the narrowing or blockage of blood vessels in or near the brain. Most often, a transient ischemic attack is caused by either an embolism or thrombosis. An embolism develops when a blood clot (or other tissue) travels through the blood to block a blood vessel in the neck or brain. Thrombosis occurs when a blood clot forms within the arteries of the brain.
What Causes a Transient Ischemic Attack?A transient ischemic attack (also known as a TIA or "mini-stroke") is a sudden episode that is caused by a temporary lack of oxygen- or nutrient-rich blood to a part of the brain. This lack of blood supply occurs because a blood vessel becomes severely narrowed or blocked.
There are several reasons why a blood vessel in the brain may become severely narrowed or blocked. The most common causes of a transient ischemic attack involve either an embolism or thrombosis. An embolism develops when a blood clot or other tissue from another part of the body (such as the heart) moves through the blood into the neck or brain.
Thrombosis occurs when a blood clot (known as a thrombus) forms within a blood vessel of the brain or neck. Unlike an embolism, with thrombosis the blood clot does not break free.
A third way in which a blood vessel can become narrowed or blocked involves stenosis (a severe narrowing of an artery), which may occur in an artery in or leading to the brain. In most cases, stenosis is the result of a plaque buildup. Such narrowing may eventually completely block the artery.
These possible causes of a transient ischemic attack are the same as those for an ischemic stroke (see Stroke Causes). The difference between a TIA and a stroke is one of duration. By definition, a stroke produces symptoms that last for at least 24 hours. A TIA causes symptoms that improve after a shorter period of time (usually within 30 minutes).