Thunderclap headache is a common presentation in the emergency department and, although multiple causes have been described, subarachnoid hemorrhage (SAH) is the primary concern and early diagnosis is critical. CT is highly sensitive if performed within 6 hours of onset. Patients with aneurysmal or perimesencephalic SAH should be evaluated with CT angiography. Further work-up should be guided by the pattern of blood. Patients with negative CT angiography may be further evaluated with MR imaging, especially patients with peripheral convexity SAH.
