1. Vilhelm Magnus Laboratory for Neurosurgical Research, Institute for Surgical Research, University of Oslo, Rikshospitalet-Radiumhospitalet, Oslo, Norway.
2. Department of Neurosurgery, Ullevål University Hospital, Rikshospitalet-Radiumhospitalet, Oslo, Norway.
3. Department of Neurosurgery, Rikshospitalet-Radiumhospitalet, Oslo, Norway.