1. Department of Otolaryngology-Head and Neck Surgery; Mayo Clinic School of Medicine; Rochester Minnesota U.S.A
2. Department of Neurologic Surgery; Mayo Clinic School of Medicine; Rochester Minnesota U.S.A
3. Department of Neurosurgery; Haukeland University Hospital; Norway
4. Department of Otolaryngology-Head and Neck Surgery; Haukeland University Hospital; Norway
5. Department of Clinical Medicine; University of Bergen; Norway