1 Department of Neurosurgery, Helsinki University Hospital and University of Helsinki, Bridge Hospital, HUS, Haartmaninkatu 4, Po. Box 340, 00029, Helsinki, Finland. elias.oulasvirta@hus.fi.
2 Department of Neurosurgery, Helsinki University Hospital and University of Helsinki, Bridge Hospital, HUS, Haartmaninkatu 4, Po. Box 340, 00029, Helsinki, Finland.
3 Department of Neurosurgery, Oulu University Hospital, Oulu, Finland.