Natural history of symptomatic intracranial arterial stenosis.

Patients who have had a stroke or transitory ischemic attack (TIA) attributed to stenosis (50-99%) of a major intracranial artery face a 12-14% risk of subsequent stroke during the 2-year period after the initial ischemic event, despite treatment with antithrombotic medications. Most of this risk accrues during the first year. Some patients are at substantially greater risk, particularly those with a severe (70-99%) stenosis, those who have recently had an ischemic event, and women. Patients may also be at high risk if they had an initial stroke rather than TIA or if they have symptoms precipitated by hemodynamic maneuvers. The annual risk of subsequent stroke may exceed 20% in these high-risk groups.