What are the criteria from the International Headache Society for subarachnoid hemorrhage?
- 1. Severe headache of sudden onset fulfilling criteria C and D
- 2. Neuroimaging (CT or MRI T2 or flair sequences) or cerebrospinal fluid evidence of nontraumatic subarachnoid hemorrhage with or without other clinical signs
- 3. Headache develops simultaneously with hemorrhage
- 4. Headache resolves within 1 month