1 From the Department of Neurology (C.M.M.), University of Washington, Seattle; and the Departments of Radiology (S.R.), Medicine (A.K.B.), Neurosurgery (K.T.K.), and Pathology (A.K.H.), Massachusetts General Hospital, and the Departments of Radiology (S.R.), Medicine (A.K.B.), Neurosurgery (K.T.K.), and Pathology (A.K.H.), Harvard Medical School - both in Boston.