1. From Departments of Neurology and Interventional Neuroradiology (R.G.N.), Massachusetts General Hospital, Boston, Mass; Department of Neurology (D.S.L., W.S.S.), University of California, Los Angeles, Calif; Department of Neurology (G.S.), University of Southern California, Los Angeles, Calif; Department of Interventional Neuroradiology (G.D.), University of California, Los Angeles, Calif.