1 From the Departments of Neurology (I.A.-R.), Radiology (J.N.F.), Neurosurgery (G.P.D.), Medicine (C.N.K.), and Pathology (C.W.M., K.A.L.), Massachusetts General Hospital, and the Departments of Neurology (I.A.-R.), Radiology (J.N.F.), Neurosurgery (G.P.D.), Medicine (C.N.K.), and Pathology (C.W.M., K.A.L.), Harvard Medical School - both in Boston.