[1] Korea Univ, Korea Univ Guro Hosp, Dept Neurosurg, Coll Med, Seoul, South Korea
[2] Washington Univ, Dept Orthopaed Surg, St Louise, MO USA
[3] Univ Washington, Dept Neurol Surg, Seattle, WA USA
[4] Korea Univ, Korea Univ Guro Hosp, Dept Neurosurg, Coll Med, 148 Gurodongro, Seoul, South Korea