1. Department of Otorhinolaryngology-Head and Neck Surgery; Technische Universitaet Muenchen; Munich Germany
2. Department of Otolaryngology-Head and Neck Surgery; University of Pennsylvania; Philadelphia Pennsylvania U.S.A.
3. Department of Otolaryngology-Head and Neck Surgery; Thomas Jefferson University; Philadelphia Pennsylvania U.S.A.
4. Department of Otolaryngology; University of Pittsburgh School of Medicine; Pittsburgh Pennsylvania U.S.A.
5. Department of Otolaryngology; Medical College of Wisconsin; Milwaukee Wisconsin U.S.A.