1. Department of Neurosurgery, Inha Univeristy Hospital, Incheon, Korea.
2. Department of Anesthesiology, Inha Univeristy Hospital, Incheon, Korea.
3. Department of Neurosurgery, Spine and Spinal Cord Institute, Gangnam Severance Spine Hospital, Yonsei University College of Medicine, Seoul, Korea.
4. Department of Neurosurgery, Anyang TeunTeun Hospital, Anyang, Korea.