1. From the Brain Vascular Malformation Study Group, University of Toronto, Toronto Western Hospital, Division of Neurosurgery and Division of Neuroradiology, Ontario, Canada (J.M.C. v D., K.G.T., R.A.W., R.I.F., M.C.W.), and Leiden University Medical Center, Department of Neurosurgery, Leiden, the Netherlands (J.M.C. v D.).