Detection of intracranial emboli in patients with symptomatic extracranial carotid artery disease.

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Abstract
Cerebral embolism from extracranial sources is an important cause of ischemic stroke. The purpose of this limited study using long-term transcranial Doppler ultrasonographic monitoring was to estimate the frequency of clinically silent intracranial embolisms in patients with symptomatic extracranial carotid artery disease. By means of a 2-MHz pulsed-wave transcranial Doppler instrumentation, three consecutive patients with extracranial internal carotid artery stenosis (n = 2) or occlusion (n = 1) and recurrent ipsilateral ischemic events were monitored (19 hours total recording time). In addition, 10 control subjects without cerebrovascular disease were studied (25 hours total recording time). Formed-element emboli were defined as distinct signals within the fast Fourier-transform Doppler spectrum that were < 70 msec in duration and > 9dB greater in intensity than the background signal. Clinically silent formed-element embolism of ophthalmic or cerebral arteries was demonstrated in all three patients. Embolic events occurred only in the territory of the symptomatic internal carotid artery. The average rate of cerebral embolization at transcranial Doppler ultrasonography was 4.1/hr, with a mean signal duration of 47 msec. No emboli were found in control subjects. The observed high frequency of silent embolism of the intracranial arteries detected by transcranial Doppler monitoring in patients with recurrently symptomatic extracranial carotid artery disease should encourage studies of the prognostic and therapeutic implications of this method.