[1] Univ Toronto, St Michaels Hosp, Div Neuroradiol, Dept Med Imaging, Toronto, ON, Canada
[2] Univ Toronto, Dept Surg, Div Neurosurg, Toronto, ON, Canada
[3] Univ Edmonton, Dept Surg, Div Neurosurg, Edmonton, AB, Canada
[4] Univ Saskatchewan, Div Neurosurg, Dept Surg, Saskatoon, SK, Canada
[5] Univ Calgary, Dept Clin Neurosci, Div Neurosurg, Calgary, AB, Canada