1. Department of Otorhinolaryngology-Head and Neck Surgery; University Hospital Essen; Essen Germany
2. Department of Otorhinolaryngology-Head and Neck Surgery; University Hospital of Mont-Godinne; Yvoir Belgium
3. Department of Otorhinolaryngology-Head and Neck Surgery; University Hospital Marburg; Marburg Germany
4. Department of Otorhinolaryngology-Head and Neck Surgery; University Hospital Ulm; Ulm Germany
5. Department of Otorhinolaryngology-Head and Neck Surgery; Centre Hospitalier de Luxembourg; Luxembourg Belgium