1 Department of Otolaryngology-Head and Neck Surgery, Korea University College of Medicine, 80 Guro-dong, Guro-gu, Seoul, 152-703, South Korea. jgcho@korea.ac.kr.
2 Department of Otolaryngology-Head and Neck Surgery, Korea University College of Medicine, 80 Guro-dong, Guro-gu, Seoul, 152-703, South Korea.