From the Department of Neurology, Beth Israel Deaconess Medical Center (M.R.), the Departments of Neurology (N.V., M.P.F.), Radiology (G.J.H.) and Pathology (M.P.F.), Massachusetts General Hospital, and the Departments of Neurology (M.R., N.V.), Radiology (G.J.H.), and Pathology (M.P.F.), Harvard Medical School - all in Boston.