1. Clinical Centre Niš, Ear, Nose and Throat Clinic, Niš + Faculty of Medicine, Niš
2. Malteser St. Franziskus Hospital, Flensburg, Germany
3. Faculty of Medicine, Niš + Institute “Niška Banja”, Niška Banja
4. Clinical Centre Niš, Ear, Nose and Throat Clinic, Niš
5. Faculty of Medicine, Niš