[1] Yonsei Univ, Coll Med, Gangnam Severance Hosp, Dept Neurosurg,Spine & Spinal Cord Inst, Seoul 06273, South Korea
[2] Yonsei Univ, Coll Med, Grad Sch Med Sci, Brain Korea Project 21,Dept Neurosurg, Seoul 03722, South Korea
[3] Kyungpook Natl Univ Hosp, Dept Neurosurg, Daegu 41944, South Korea
[4] Yonsei Univ, Coll Med, Gangnam Severance Hosp, Dept Internal Med, Seoul 06273, South Korea