(2) No evidence of aneurysmal subarachnoid hemorrhage
(3) Normal or near-normal cerebrospinal fluid analysis (protein level <80 mg%, leukocytes <10 mm3, normal glucose level)
(4) Severe, acute headaches, with or without additional neurologic signs or symptoms.
(5) Reversibility of angiographic abnormalities within 12 weeks of symptom onset. If death occurs before the follow-up studies are completed, autopsy rules out such conditions as vasculitis, intracranial atherosclerosis, and aneurysmal subarachnoid hemorrhage, which can also manifest with headache and stroke