1. Department of Neurological Surgery, College of Medicine, Chung-Ang University, Seoul, Korea.
2. Department of Neurological Surgery, Chung-Ang University Graduate School, Seoul, Korea.
3. Department of Neurosurgery, Spine Center, Chuncheon Sacred Heart Hospital, Hallym University Medical Center, Hallym University College of Medicine, Chuncheon, Korea.
4. Department of Neurosurgery, Kyungpook National University Hospital, Daegu, Korea.
5. Division of Cardiology, College of Medicine, Chung-Ang University, Seoul, Korea.