[1] Oslo Univ Hosp Ulleval, Dept Neurosurg, Oslo, Norway
[2] Univ Oslo, Fac Med, Oslo, Norway
[3] SINTEF, Dept Hlth Res, Med Technol, Trondheim, Norway
[4] Oslo Univ Hosp Ulleval, Dept Neurol, Oslo, Norway
[5] Norwegian Air Ambulance Fdn, Oslo, Norway
[6] Univ Pretoria, Steve Biko Acad Hosp, Fac Hlth Sci, Sch Med,Dept Neurosurg, Pretoria, South Africa