1. From the Division of Neuroradiology, Department of Medical Imaging, University of Toronto and the Toronto Western Hospital, Toronto, Ontario, Canada (S.P., T.K., D.J.M., D.M.M.); Department of Neurosurgery (C.M.) and Department of Diagnostic Radiology (C.M.), Yale University School of Medicine, New Haven, CT; and Division of Neurology, Department of Medicine, University of Toronto and the Toronto Western Hospital, Toronto, Ontario, Canada (L.K.C., F.L.S.).