1. Department of Neurosurgery, Seoul St. Mary's Hospital, The Catholic University of Korea, Seoul, Korea.
2. Department of Neurosurgery, Bundang Jesaeng Hospital, Seongnam, Korea.
3. Department of Neurosurgery, St. Vincent's Hospital, The Catholic University of Korea, Suwon, Korea.
4. Department of Otolaryngology-Head and Neck Surgery, Seoul St. Mary's Hospital, The Catholic University of Korea, Seoul, Korea.