TRANSHEMISPHERIC PASSAGE OF MICROEMBOLI IN PATIENTS WITH UNILATERAL INTERNAL CAROTID-ARTERY OCCLUSION

Background and Purpose: Ischemic episodes distal to an internal carotid artery occlusion are common. We undertook this study to look for evidence of transhemispheric passage of embolic material in this patient category as a mechanism for embolic events. Methods: Seven symptomatic patients with unilateral internal carotid artery occlusion and contralateral stenosis were examined by transcranial Doppler ultrasonography with 2-MHz probe (average monitoring time, 2.5 hours per patient). Both middle cerebral arteries and (if present) the reverse-flow anterior cerebral artery ipsilateral to the occluded internal carotid were monitored. Three patients were reexamined 1 month after carotid endarterectomy. Results: Embolic signals were detected in the middle cerebral artery ipsilateral to the stenosed internal carotid artery in all seven patients and in the opposite middle cerebral artery in four patients. In these four patients, a reverse-flow anterior cerebral artery was observed in which embolic signals were detected. No embolic signals were detected after surgery in any of the three patients who underwent carotid endarterectomy. Conclusions: Transhemispheric passage of embolic material occurs in patients with unilateral internal carotid artery occlusion and contralateral stenosis. Endarterectomy of the stenosed internal carotid artery may eliminate the detected embolic signals in both hemispheres. Transcranial Doppler ultrasonography could be used as a diagnostic tool to identify the embolic source in patients with unilateral carotid occlusion.