1. Department of Neurosurgery, Shimane University Faculty of Medicine, 89-1 Enya, Izumo, Shimane 693-8501, Japan
2. Department of Neurosurgery, Sakurakai Hospital, 5-2610-1 Handa, Sayama, Osaka 589-0011, Japan
3. Department of Organ Pathology, Shimane University Faculty of Medicine, 89-1 Enya, Izumo, Shimane 693-8501, Japan