Urgent CT showed bilateral mild cortical SAH however angioCT did not disclose aneurysms, revealing a left inner carotid artery (ICA) stenosis interpreted as dissection. Brain MRI confirmed cortical SAH without evidence of ischemic lesions or other microbleedings and angiography showed widespread thinning of the pericallosal and callosomarginal arteries, suggestive for vasospasm. She was diagnosed with RCVS and put on nimodipine, however patient continued to complain about headache and a second MRI showed an asymptomatic ischemic lesion. Thrombophilic and immunological screening were negative and cerebrospinal fluid isoElettroFocusing revealed oligoclonal bands. Whole-body FDG-PET confirmed circumscribed inflammation involving left ICA walls and excluded other vessels’ involvement. She was treated with high-dose steroids with headache remission and then put on immunosuppressant treatment with also radiological improvement and vascular abnormalities resolution.