[1] KAROLINSKA HOSP, DEPT OTORHINOLARYNGOL, S-10401 STOCKHOLM 60, SWEDEN
[2] CENT HOSP SKOVDE, DEPT OTORHINOLARYNGOL, SKOVDE, SWEDEN
[3] LINKOPING UNIV HOSP, DEPT OTORHINOLARYNGOL, S-58185 LINKOPING, SWEDEN
[4] CENT HOSP SUNDSVALL, DEPT OTORHINOLARYNGOL, SUNDSVALL, SWEDEN
[5] UNIV LUND HOSP, DEPT OTORHINOLARYNGOL, S-22185 LUND, SWEDEN
[6] CENT HOSP OREBRO, DEPT OTORHINOLARYNGOL, OREBRO, SWEDEN
[7] CENT MIL HOSP, HELSINKI, FINLAND
[8] CITY HOSP, REYKJAVIK, ICELAND
[9] UNIV HOSP OULU, OULU, FINLAND
[10] CENT HOSP VASTERVIK, VASTERVIK, SWEDEN