1. Department of Neurosurgery, Yeouido St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
2. Department of Neurosurgery, Bucheon St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Bucheon, Korea.
3. Department of Neurosurgery, St. Paul's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.