1. Department of Neurosurgery, University of Essen, Essen, Germany
2. Department of Neurosurgery, Dortmund Hospital, Dortmund, Germany
3. Division of Neurosurgery, Hamilton General Hospital, Hamilton, Canada
4. Department of Oto-Rhino-Laryngology, University of Essen, Essen, Germany
5. Institute of Radiology, Neuroradiology and Interventional Radiology, University of Essen, Essen, Germany
6. Department of Neurosurgery, University Hospital Magdeburg, Magdeburg, Germany