The plaque may also be the source of cholesterol or platelet emboli even with a minor degree of stenosis. Formation of a thrombus may completely occlude the artery. This must be recognized because the TIAs herald the high probability of a vascular catastrophe, and this recognition may allow prevention of a stroke. The most frequent site of the atheromatous plaque causing a stroke is at the origin of the internal carotid artery. TIAs usually last from a few seconds to several minutes.
Recurrent attacks are usually of the same general type.
One type of TIA involves only the eye and is called transient monocular blindness. More characteristically there is the sudden onset of a gray-black shade gradually descending or ascending to obscure vision and then gradually recovering. Other TIAs in the carotid artery circulation may be associated with speech disturbance, numbness and weakness of the hand and arm or the arm and leg, or numbness of the face. Usually the neurological examination is normal because the patient recovers completely between attacks. A bruit heard over the neck suggests stenosis in the proximal internal carotid artery and requires further evaluation with carotid noninvasive studies, and magnetic resonance imaging is indicated.