1. Department of Medicine, Faculty of Health, Witten/Herdecke University, Witten
2. Department of Neurosurgery, St. Barbara-Hospital, Academic Hospital of Westfälische Wilhelms-University Münster, Hamm
3. Department of Neurosurgery, Academic Hospital Köln-Merheim, University of Witten/Herdecke, Witten
4. Department of Neurosurgery, Niels-Stensen-Kliniken, Marienhospital Osnabrück, Osnabrück
5. Department of Neurosurgery, Asklepios Paulinen Hospital, Wiesbaden, Germany