The primary role of the brain is to send signals to the body for motor function and respond to receive signals received through the five senses (sight, hearing, touch, smell, and taste). The brain processes information both through conscious thought, and unconsciously through the nervous systems that control basic bodily functions, like heart rate, breathing, and temperature control.
The brain is arranged so that the right side of the brain controls the left side of the body, and the left side of the brain controls the right of the body.
Vision is located in the back of the brain (occiput), and balance and coordination are located at the bottom of the brain (cerebellum).
Blood supply to the brain comes from the two carotid arteries that are located in the front of the neck, and the two vertebral arteries that run in the back of the neck through small canals in the bony spine (vertebrae).
All four arteries connect at a junction of blood vessels located in the base of the brain (called the Circle of Willis), and from there smaller arteries branch out to supply the brain with oxygen and nutrients.
When a portion of the brain loses its blood supply, it can become damaged and stop functioning. When a portion of the brain does not function, the part of the body that it controls also stops working.
This is called a stroke or a cerebrovascular accident (CVA). If the brain is able to regain its blood supply quickly, then the CVA symptoms may resolve; this is known as a transient ischemic attack (TIA).
A TIA is a stroke that resolves by itself.
Why do some clots dissolve while others don’t?
According to Dr. Emil Matarese, director of a primary stroke center at St. Mary’s Medical Center in Langhorne, Pa., the body has naturally occurring clot-busting agents.
“Eventually all clots will dissolve, but whether there is damage depends on how long the clot is in place,” Dr. Matarese said. However, because there is no way to predict when a clot will dissolve on its own, time is of the essence.
“Whenever you have stroke symptoms, dial 9-1-1 immediately and get to the emergency room so you can be evaluated. Don’t wait to see if the symptoms go away.”
While the vast majority of strokes are not preceded by TIA, about a third of people who experience TIA go on to have a stroke within a year.
“TIA is a warning stroke and gives a patient time to act and keep a permanent stroke from occurring,” Dr. Matarese said.
“By recognizing TIA symptoms and getting to the hospital, the patient can get help in identifying why the TIA occurred and get treatment — either through medication or surgery — that can prevent a stroke from occurring.”
If a survivor experiences TIA after they have had a stroke, they should go to the emergency room immediately because something in their treatment plan has not worked.
In essence, according to Dr. Matarese, there should be no difference in response to a TIA or a stroke.
Although a TIA resolves itself before there is damage, there is no way to predict which clots will dissolve on their own.
Stroke — and TIA — are medical emergencies; dial 9-1-1 and tell the operator you think it’s a stroke and note the time the symptoms started. Remember: Time lost is brain lost.
What are the causes of transient ischemic attack (TIA)?
Loss of blood supply to portions of the brain may occur for a variety of reasons. A blood vessel can become blocked, and blood supply to a part of the brain is lost, or a blood vessel can leak blood into the brain (brain hemorrhage).
Most commonly however, the blood vessel is blocked. The blockage can be caused by a blood clot that forms in the blood vessel (thrombosis) or it can be caused by a clot or debris that floats downstream (embolus).
What are the risk factors for transient ischemic attack (TIA)?
The risk factors for TIA or stroke are the same as those for other vascular disease, similar to heart attack (coronary artery disease) or peripheral vascular disease, which causes decreased blood flow to the legs.
These risk factors include:
- family history
- high blood pressure,
- high cholesterol, and
Moreover, any condition that results in stagnant blood flow and or clotting may result in a TIA due to embolization of a blood clot.
Such conditions may include atrial fibrillation, large heart attacks, and severe weakness of the heart muscle (cardiomyopathy) .
What are the symptoms of transient ischemic attack (TIA)?
The intensity and location of the blood limitation to the brain will determine what symptoms will occur as a result of a stroke or TIA.
Many people experience confusion, weakness, and lethargy. If the loss of blood supply is in an area supplied by the middle cerebral artery, a classic sign may include weakness or paralysis and numbness of one side of the body. The whole side may be affected, or just one limb.
Often there is a facial droop. If the stroke is on the left side of the body where the speech centers are usually located, there may be difficulty understanding words or speaking. Partial vision loss may also be part of the constellation of symptoms.
Strokes involving the vertebral arteries decrease blood supply to the base of the brain and may cause a drop attack (a sudden fall while walking or standing, and then a quick recovery), an unexpected collapse, incoordination, or difficulty walking.
The important distinction between stroke and TIA is resolution of the symptoms. By definition, the symptoms of a TIA must completely resolve.
And, while this most often occurs within the first few minutes after symptom onset, it may take up to 24 hours to have complete return to normal function.
A special type of TIA is amaurosis fugax. Transient blindness in one eye occurs because debris from a narrowed carotid artery clogs the artery (ophthalmic artery) that supplies blood to the retina of the eye.
How is transient ischemic attack (TIA) diagnosed?
TIA is diagnosed by history and physical examination. Since most often the symptoms have resolved, the physician will need to complete a thorough history from the patient and family or friends who witnessed the event.
The physical exam will include careful attention to the neurologic examination. This may include:
- Assess mental status to make certain the patient is alert and oriented.
- Check eye range of motion and facial movement to evaluate the cranial nerves (the short nerves that run from the brain to the face and neck).
- Listen to the neck with a stethoscope to detect abnormal sounds that may signal narrowing of the blood vessel (carotid bruits).
- Check for a regular heart rhythm to rule out the presence of atrial fibrillation.
- Examine the arms and legs for tone, power, and sensation.
- Check coordination and balance.
If the diagnosis of TIA is made, further urgent testing is usually recommended, including:
- Electrocardiogram (EKG) to confirm a regular heart rate
- Computerized tomography (CT scan) of the brain to assess bleeding
- Carotid ultrasound to assess for narrowing of the large blood vessels in the neck
- Some hospitals have CT angiogram available to evaluate the cerebral, carotid, and vertebral arteries. This test is the same as a CT of the head with the addition of intravenous dye into the blood vessels to the arteries.
- Routine blood tests may include a complete blood count (CBC) to assess for anemia (low red blood cell count) or too few platelets (thrombocytopenia). If the patient takes warfarin (Coumadin), a blood thinner, then an international normalized ratio (INR – a blood test that measures the degree of blood thinning) or prothrombin time (PT), may be performed to assess blood clotting measurements.
If there is concern that the heart is the source of blood clot or debris, then an echocardiogram or sound wave tracing of the heart may be considered.