Dr. QU Jin-rong is now working in Department of Radiology, Affiliated Cancer Hospital, Zhengzhou University, Zhengzhou, Henan 450008, China. Correspondence to: DAI Jian-ping, Department of Neuroradiology, Beijing Tiantan Hospital, Capital Medical University, Beijing 100050, China (Tel: 86-10-65112164. Fax: 86-10-65112164. Email: doctor_hnchr@yahoo.com.cn); Dr. JIANG Tao, Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing 100050, China (Tel: 86-10-67098039. Fax: 86-10-69036038. Email: jiangtao369@sohu.com)