1 Department of Otolaryngology-Head and Neck Surgery, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, North 15 West 7, Sapporo 060-8638, Japan.
2 Department of Otolaryngology-Head and Neck Surgery, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, North 15 West 7, Sapporo 060-8638, Japan. Electronic address: ak-homma@med.hokudai.ac.jp.