This patient describes her headache as severe, sudden-onset, and different than her prior headaches. These clues on history should raise concern for a subarachnoid hemorrhage (SAH) as the cause of her headache. Choice A (Lumbar Puncture) helps evaluate headaches caused by meningitis, pseudotumor cerebri (idiopathic intracranial hypertension), and SAH. Choice B (IV 1000mL 0.9% NaCl) is sometimes used to treat headaches, like migraines, but this patient should first receive another testing as there is a concern for SAH. Choice C (IV Ceftriaxone) is the correct initial treatment for bacterial meningitis, but this patient has a higher pretest probability for SAH. Choice D (Non-contrast CT head) is the right answer. Non-contrast CT scan of the brain performed within 6 hours of headache onset have high sensitivity to rule out aneurysmal SAH. The sensitivity of the non-contrast CT scan diminishes to 91-93% at 24hours after headache onset and continues to decrease after this to 50% sensitivity at seven days after pain onset. Lumbar puncture is recommended for a patient with a negative CT scan, high pretest probability for SAH, and presentation after 6 hours of headache onset. Findings on Lumbar Puncture that support the diagnosis of SAH include Xanthochromia (yellow appearance of the CSF due to blood breakdown) and inadequate clearing of red blood cells in the CSF between tubes 1 and 4. Treatment for SAH includes blood pressure control, seizure prophylaxis, and neurosurgical consultation, and nimodipine to prevent vasospasm and rebleeding. The Hunt and Hess scoring system can be used to predict clinical outcomes for patients with SAH. Correct Answer: D