1. Department of Neurosurgery, Yongin Severance Hospital, Yonsei University College of Medicine, Yongin, Korea.
2. Department of Neurosurgery, Leon Wiltse Memorial Hospital, Suwon, Korea.
3. Department of Neurosurgery, The Spine and Spinal Cord Institute, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.