Prespecified subgroup analyses will be performed according to the clinical presentation: 1) isolated headache; 2) isolated intracranial hypertension (headache and papilledema); 3) Focal neurological deficits and/or seizures and/or disturbances of consciousness. Furthermore, prespecified subgroup analyses will be performed according to modes of onset: 1) acute (symptoms < 48 hours duration); 2) subacute (symptoms > 48 hours and < 7 days duration); 3) chronic (symptoms > 7 days duration).