[1] Univ Toronto, St Michaels Hosp, Dept Surg, Div Neurosurg, 30 Bond St, Toronto, ON M5B 1W8, Canada
[2] Univ Toronto, Toronto Western Hosp, Dept Surg, Div Neurosurg, 399 Bathurst St, Toronto, ON M5T 2S8, Canada
[3] Univ Coll Cork, Sch Med, Grad Entry Med, Coll Rd, Cork T12 K8AF, Ireland
[4] Univ Toronto, St Michaels Hosp, Li Ka Shing Knowledge Inst, 209 Victoria St, Toronto, ON M5B 1T8, Canada