1. Department of Neurosurgery, Fukushima Medical University, Fukushima, Fukushima, Japan
2. Department of Neurosurgery, Masu Memorial Hospital, Nihonmatsu, Fukushima, Japan
3. Department of Neurosurgery, Southern Tohoku Research Institute for Neuroscience, Southern Tohoku Hospital, Koriyama, Fukushima, Japan
4. Department of Neurosurgery, Japanese Red Cross Society Fukushima Hospital, Fukushima, Fukushima, Japan
5. Department of Neurosurgery, Minamisoma Municipal General Hospital, Minamisoma, Fukushima, Japan
6. Department of Neurosurgery, Ohta-Nishinouchi Hospital, Koriyama, Fukushima, Japan