1. Department of Neurosurgery, Erasmus Medical Center , Rotterdam , The Netherlands
2. Department of Neurosurgery, Haaglanden Medical Center , The Hague , The Netherlands
3. Department of Neurosurgery, University Hospital–Leuven , Leuven , Belgium
4. Department of Neurosurgery, University Hospital–Bern , Bern , Switzerland
5. Department of Neurosurgery, Massachusetts General Hospital/Harvard Medical School , Boston, Massachusetts , USA
6. Department of Neurosurgery, University of California , San Francisco, California , USA