Diagnosing Transient Ischemic Attacks (TIA)

  In people who have had TIAs or small strokes, it is important to determine the source of these attacks in order to prevent a major stroke. A physician will usually require a complete blood count, chest x-ray, and electrocardiogram. The physician usually first examines the carotid artery to determine if it is severely narrowed; if it is, the patient is in danger of a major stroke. Sometimes a clue to a blocked carotid artery is a whooshing sound, known as a bruit, caused by blood flow turbulence in the narrowed artery. A physician may be able to hear a bruit using a stethoscope; occasionally, even a patient can hear the sound. The presence of a bruit, however, is not necessarily a sign of an impending stroke, nor does the absence of a bruit indicate an unblocked artery. The blood pressure to the eye may also be measured; if blood flow to the eye is reduced, the physician estimates that the carotid artery is probably severely narrowed.

 A number of noninvasive imaging techniques may also be used. Carotid duplex ultrasound can measure the width of the artery, and some experts believe it may be accurate enough to be the sole method for determining whether a patient requires carotid endarterectomy. An MRI is a more elaborate and accurate way of evaluating the blood vessels and the brain's circulation, but it is also very expensive. This technique can even identify silent brain injuries in elderly patients with neurologic impairment but no symptoms of stroke.

 If less invasive tests indicate a need for surgery, cerebral angiography may be used. (This procedure can also detect aneurysms.) This requires the insertion of a catheter into the groin, which is then threaded up through the arteries to the base of the carotid artery. At this point a dye is injected and x-rays are taken to determine the location and extent of the narrowing, or stenosis, of the artery. It should be noted that the risk of stroke itself increases using this technique, particularly in elderly people with diabetes.

  Diagnosing a Major Stroke

To save a patient's life, a fast diagnosis of both the presence and type of stroke is critical. The first step is to determine whether symptoms actually indicate a stroke. Studies have shown that simple verbal and physical tests called the Los Angeles Paramedic Stroke Screen enabled emergency teams to identify 93% of stroke patients. The next important step is to determine its exact cause as quickly as possible, since new clot-busting drug therapies are effective only in the first three hours but they cause bleeding and can be lethal if the stroke is actually caused by a hemorrhage. An early-performed CT scan is accurate for diagnosing about 95% of hemorrhagic strokes. If the CT scan is negative, but the physician still suspects a hemorrhagic stroke, a spinal tap may be indicated. Spinal fluid containing significant amounts of blood will usually confirm a hemorrhagic stroke. Evidence of ischemic stroke will usually show up on a CT scan after a few days. Advances in MRI are providing very sensitive visualizations of the arteries in the brain and even of blood flow itself. All the noninvasive techniques for diagnosing transient ischemic attacks are also used for major strokes. A cardiac evaluation using an electrocardiogram and usually an echocardiogram is always done when an ischemic stroke is suspected; a technique called transesophageal echocardiography appears to be particularly useful. The presence of atrial fibrillation is a good indicator of an ischemic stroke caused by an embolism. The possibility of an accompanying serious heart disorder should also be evaluated. Blood tests may predict severity and complications after a stroke; one test uses a ratio based on the brain enzymes eolase and carnosinase, and another predicts severity from high levels of glutamate, an amino acid.