1 Department of Neurosurgery, National Health Insurance Service Ilsan Hospital, Goyang, Korea; Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Korea.
2 Department of Neurosurgery, Spine and Spinal Cord Institute, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea. Electronic address: NSKHK@yuhs.ac.