[1] Univ Hosp Geneva, Dept Neurosurg, Rue Gabrielle Perret Gentil 4, CH-1211 Geneva 14, Switzerland
[2] Univ Hosp Essen, Dept Neurosurg, Essen, Germany
[3] Univ Hosp Geneva, Dept Diagnost & Intervent Neuroradiol, Geneva, Switzerland
[4] Univ Toronto, Toronto Western Hosp, Dept Neurosurg, Toronto, ON, Canada