1. Department of Neurosurgery, Germans Trias i Pujol University Hospital, Barcelona;
2. Department of Neurosurgery, Hospital Clinic de Barcelona, Universidad de Barcelona;
3. Department of Neurosurgery, Donostia University Hospital, Guipúzcoa; and
4. Department of Neurosurgery, Hospital Universitario Río Hortega, Valladolid, Spain