Subarachnoid Hemorrhage: When a Brain Aneurysm Bleeds07/01/2016 Tagged With: aneurysm, arteriogram, arteriovenous malformation, bleed, CT. Scan, nimodipine, rupture, subarachnoid hemorrhage, thunderclap headacheAlthough most headaches–even severe ones–are due to benign factors, when a headache is due to a bleeding aneurysm it is a medical emergency.