Importance of intracranial atherosclerotic disease in patients with symptomatic stenosis of the internal carotid artery

Background and Purpose-The estimated prevalence of intracranial atheroscler otic disease (IAD) in patients with stenosis of the extracranial internal c arotid artery (ICA) varies between 20% and 50%. The benefits of carotid end arterectomy (CE) in patients with both IAD and symptomatic extracranial ICA stenosis are uncertain. Methods - The association between IAD and other vascular risk factors and w ith the risk of stroke at 3 years were studied in patients with symptomatic extracranial ICA stenosis who participated in the North American Symptomat ic Carotid Endarterectomy Trial (NASCET). Since the NASCET protocol exclude d severe IAD, only a modest number of patients in this category could be st udied. Results - IAD was observed in one third of the patients, In medically treat ed patients, the relative risk of stroke associated with IAD varied from 1. 3 (95% CI, 0.9 to 1.9) with extracranial ICA stenosis of <50% to 1.8 (95% C I, 1.1 to 3.2) with 85% to 99% ICA stenosis. In contrast, IAD did not affec t the risk of stroke among surgically treated patients. To prevent 1 stroke ipsilateral to the symptomatic ICA stenosis over 3 years in patients who h ave also IAD, 12 patients with 50% to 69%, 5 patients with 70% to 84%, and 3 patients with 85% to 99% ICA stenosis have to undergo CE, In patients wit hout IAD these numbers are 26, 7, and 6, respectively. Conclusions - IAD is an independent risk factor for subsequent stroke in me dically treated patients with symptomatic ICA stenosis. CE reduces this ris k, The additional risk imposed by IAD in medically treated patients enhance s the value of CE in patients with moderate symptomatic extracranial ICA st enosis. Detection of IAD, requiring angiography, is an important prelude to planning CE in symptomatic patients with moderate extracranial ICA stenosi s.