Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 86. Stroke

Topics: Introduction | Transient Ischemic Attacks | Ischemic Stroke | Hemorrhagic Stroke

Transient Ischemic Attacks

A transient ischemic attack (TIA) is a temporary disturbance in brain function resulting from a temporary blockage of the brain's blood supply.

TIAs may be a warning sign of an impending ischemic stroke. About one third of people who have had at least one TIA will have an ischemic stroke; about half of these strokes occur within 1 year of the TIA. People who have had a TIA are almost 10 times more likely to have a stroke than those who have not. Recognizing a TIA and having the cause identified can help prevent a stroke. Causes of TIAs and ischemic strokes are the same. Most TIAs occur when a piece of a blood clot (thrombus) or of fatty material (an atheroma) due to atherosclerosis breaks off from the heart or from the wall of an artery, travels through the bloodstream (becoming an embolus), and lodges in an artery that supplies the brain. Atherosclerosis causes recurring TIAs in about 5% of people.

Symptoms and Diagnosis

Symptoms of a TIA develop suddenly. They are identical to those of an ischemic stroke (see Section 6, Chapter 86) but are temporary and reversible. They usually last 2 to 30 minutes and rarely last more than 1 to 2 hours. By definition, they do not last longer than 24 hours. Apparently, no permanent damage results, because the blood supply to the affected area is restored relatively quickly. However, TIAs tend to recur. A person may have several in 1 day or only two or three in several years.

People who have a sudden, temporary symptom similar to any symptom of a stroke should report it to a doctor. Such a symptom suggests a TIA. However, other disorders, including seizures, brain tumors, migraine headaches, and abnormally low levels of sugar in the blood, have similar symptoms, so further evaluation is needed.

Doctors use several procedures to determine whether an artery to the brain is blocked, which artery is blocked, and how complete the blockage is. These procedures include listening with a stethoscope for the sounds made by turbulent blood flow (bruits) in the internal carotid arteries (in the neck), color Doppler ultrasonography of the internal carotid and vertebral arteries, and sometimes magnetic resonance angiography (see Section 6, Chapter 77) and cerebral angiography (see Section 6, Chapter 77). Imaging procedures, such as computed tomography (CT) or magnetic resonance imaging (MRI), cannot be used to identify TIAs because TIAs, unlike strokes, usually do not cause brain damage. A specialized type of MRI, called diffusion MRI, can identify abnormal areas of brain tissue that are temporarily nonfunctional but that do not die (that is, that do not result in stroke).

Treatment

Treatment of TIAs is aimed at preventing a stroke. The first step in preventing a stroke is to control, if possible, the major risk factors for it: high blood pressure, high cholesterol levels, smoking, and diabetes. In addition, antiplatelet drugs, such as aspirin and dipyridamole, can be taken. When stronger drugs are needed (for example, for people who have atrial fibrillation, another abnormal heart rhythm, or a heart valve disorder), doctors may prescribe anticoagulants (drugs used to inhibit blood clotting), such as heparin or warfarin.

The degree of narrowing in the carotid arteries helps doctors determine the treatment. If the internal carotid artery is narrowed by more than 70% and the person has had strokelike symptoms during the previous 6 months, an operation to widen the artery (called an endarterectomy) may be performed to reduce the risk of having a stroke. When the artery is less narrowed, the operation is performed to prevent the blockage of the artery over time or to prevent additional TIAs or strokes if either are thought likely. An endarterectomy usually involves removing fatty deposits (atheromas) and clots in the internal carotid artery. The operation has a 2 to 6% risk of causing a stroke (because the operation may dislodge clots or other material that can then travel through the bloodstream and block an artery). For people who have minor narrowing and no symptoms, the risk of having a stroke is higher during the operation than it is with drug therapy. However, the risk is lower after the operation for several years than it is with drug therapy.

In other narrowed arteries, such as the vertebral arteries, endarterectomy may not be possible because the operation is more difficult to perform in these arteries than in the internal carotid arteries.

Alternatively, angioplasty (see Section 3, Chapter 33) may be performed. In this procedure, a catheter with a balloon at its tip is threaded into the narrowed artery. The balloon is then inflated for several seconds to widen the artery. To keep the artery open, doctors insert a tube made of wire mesh (a stent) into the artery. This procedure is considered experimental but in the future is likely to replace endarterectomy.