1. Department of Otolaryngology/Head and Neck Surgery, School of Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke 329-0498, Japan
2. Department of Otolaryngology, Shin-Oyama City Hospital, 1-1-5 Wakagi-cho, Oyama 323-0028, Japan
3. Department of Pathology, School of Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke 329-0498, Japan