1. Department of Neurosurgery, Incheon St. Mary’s Hospital, The Catholic University of Korea College of Medicine, Dongsuro 56, Bupyeong-gu, Incheon 403-720, Republic of Korea
2. Department of Neurosurgery, Seoul St. Mary’s Hospital, The Catholic University of Korea College of Medicine, Banpodaero 222, Seocho-gu, Seoul 137-701, Republic of Korea