[1] Hosp Sick Children, Dept Pediat, Div Neurol, Toronto, ON M5G 1X8, Canada
[2] Univ Dusseldorf, Dept Gen Pediat Neonatol & Pediat Cardiol, Univ Childrens Hosp, Moorenstr 5, D-40225 Dusseldorf, Germany
[3] Hosp Sick Children, Dept Pediat, Div Hematol & Oncol, Toronto, ON M5G 1X8, Canada
[4] Johns Hopkins Univ Hosp, Div Pediat Neurol, Dept Neurol, Baltimore, MD 21287 USA
[5] Johns Hopkins Med Inst, Russell H Morgan Dept Radiol & Radiol Sci, 600 N Wolfe St, Baltimore, MD 21205 USA