Abbreviations: CBF, cerebral blood flow; CT, computed tomography; CTA, comuted tomography angiography; FLAIR, fluid-attenuated inversion recovery; IMP, -isopropyl[123I]-p-iodoamphetamine; MRA, magnetic resonance angiography; RI, magnetic resonance imaging; RCVS, reversible cerebral vasoconstriction synrome; SAH, subarachnoid hemorrhage; SPECT, single photon emission computed omography. ∗ Corresponding author at: Department of Neurosurgery, Nippon Medical School, -1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan. Tel.: +81 3 3822 2131; ax: +81 3 5685 0986. E-mail addresses: shunchan.ryouchan@gmail.com, s00-078@nms.ac.jp, 00-080@nms.ac.jp (F. Matano).