1. Department of Neurosurgery, College of Medicine, Yonsei University, Gangnam Severance Hospital, Seoul 06273, Republic of Korea
2. Department of Neurosurgery, College of Medicine, Eulji University, Daejeon Eulji University Hospital, Daejeon 34824, Republic of Korea
3. Department of Neurosurgery, College of Medicine, National Health Insurance Service, Yonsei University, Ilsan Hospital, Ilsan 10444, Republic of Korea
4. Department of Neurosurgery, Wiltse Memorial Hospital, Suwon 16480, Republic of Korea