1. From the Departments of Surgery (Neurosurgery) (M.A.S., P.J.P., M.C.W.) and Radiology (Neuroradiology) (P.J.P., K.G.tB., W.M., R.A.W.), University of Toronto, Toronto, Ontario, Canada; Faculty of Medicine, Federal University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil (M.A.S.); and University of Toronto Brain Vascular Malformation Study Group, Toronto, Ontario, Canada (P.J.P., K.G.tB., W.M., R.A.W., M.C.W.).