1. Department of Neurosurgery, University of Kentucky, Chandler Medical Center, Lexington, KY 40536-0298, USA
2. Department of Pathology, University of Kentucky, Chandler Medical Center, Lexington, KY 40536-0298, USA
3. Department of Orthopedic Surgery, University of Kentucky, Chandler Medical Center, Lexington, USA
4. Department of Neurology, University of Kentucky, Chandler Medical Center, Lexington, KY 40536-0298, USA