1. Department of Otolaryngology, Head and Neck Surgery, Graduate School of Medicine, Hokkaido University, N15W7, Kita-ku, Sapporo 0608638, Japan
2. Department of Otolaryngology, Head and Neck Surgery, Teine-Keijinkai Hospital, 12-1-40 Maeda 1-Jo, Teine-Ku, Sapporo 0068555, Japan