From the Department of Neurology, Boston Children's Hospital (M.P.G.), the Departments of Neurology (G.Y.G., R.L.T.), Radiology (W.A.M.), and Pediatrics (R.L.T.), Massachusetts General Hospital, and the Departments of Neurology (M.P.G., G.Y.G., R.L.T.) and Radiology (W.A.M.), Harvard Medical School - all in Boston.