[1] Tsukuba Med Ctr Hosp, Dept Neurosurg, Tsukuba, Ibaraki, Japan
[2] Koyama Mem Hosp, Dept Neurosurg, Kashima, Ibaraki, Japan
[3] Univ Tsukuba, Fac Med, Dept Neurosurg, Tennodai 1 1 1, Tsukuba, Ibaraki 3058575, Japan
[4] Univ Tsukuba, Fac Med, Div Stroke Prevent & Treatment, Tsukuba, Ibaraki, Japan
[5] Dokkyo Med Univ, Saitama Med Ctr, Dept Neurosurg, Koshigaya, Saitama, Japan
[6] Toranomon Gen Hosp, Dept Neuroendovasc Therapy, Tokyo, Japan
[7] Natl Hosp Org Mito Med Ctr, Dept Neurosurg, Higashi, Ibaraki, Japan