1. Department of Neurosurgery, University Hospitals of Geneva, CH-1205 Geneva, Switzerland
2. Faculty of Medicine, University of Geneva, 1206 Geneva, Switzerland
3. Department of Neurosurgery, Pontchaillou Hospitals, CEDEX 9, F-35033 Rennes, France
4. Centre Hospitalier Universitaire Caen Normandie, F-14000 Caen, France