1. Department of Neurosurgery, Kangwon National University Hospital, Kangwon National University College of Medicine, Chuncheon, Korea.
2. Department of Neurosurgery, Kunkuk University Chungju Hospital, Chungju, Korea.
3. Department of Neurosurgery, Wonju Severance Christian Hospital, Yonsei University Wonju College of Medicine, Wonju, Korea.