What is the most appropriate diagnostic evaluation for a patient with a severe headache, nausea, and dizziness, and a history of migraines?

Diagnostic Evaluation for Suspected Subarachnoid Hemorrhage

This patient requires noncontrast CT of the head immediately, followed by CTA of the head if the initial CT is negative. 1

Clinical Reasoning

This presentation represents a thunderclap headache (sudden severe headache described as "worst headache ever") with associated nausea and dizziness—a classic presentation requiring urgent evaluation for subarachnoid hemorrhage (SAH). 1 Despite her history of migraines, the acute onset during exertion, severity ("worst headache she has ever had"), and failure to respond to typical migraine medications distinguish this from her baseline migraine pattern. 1

Initial Imaging: Noncontrast CT

• Noncontrast CT is the cornerstone for diagnosing acute SAH, with a sensitivity of 98% and specificity of 99% in the acute setting. 1
• CT is preferred over MRI initially because it is faster, more readily available in emergency settings, and superior for detecting acute blood products. 1, 2
• The examination is normal, but this does not exclude SAH—neurologic deficits are absent in many cases of serious intracranial pathology. 1

Sequential Imaging: CTA if CT is Negative

• If the noncontrast CT is negative but clinical suspicion remains high (as in this case), CTA should follow immediately to evaluate for aneurysms or other vascular abnormalities. 1, 3
• The ACR Appropriateness Criteria specifically state that CTA is appropriate in thunderclap headache settings, especially if SAH is suspected, as it allows rapid evaluation for aneurysms and is comparable to conventional angiography. 1
• In patients with acute severe headache, normal neurological examination, and normal noncontrast CT, CTA identifies vascular abnormalities in approximately 7.4% of cases, with aneurysms being the most common finding (5.4%). 3

Why Not Other Options?

• CTA alone (without initial noncontrast CT): This would miss acute hemorrhage, as CTA is optimized for vascular structures, not blood products. 1
• MRI alone: While MRI with specific sequences (FLAIR, SWI/GRE) can detect SAH, conventional MRI sequences are insensitive (sensitivity varies from 50-94% for acute SAH), and MRI is less available emergently and requires more time. 1, 2
• Noncontrast CT alone: This misses the opportunity to identify an underlying aneurysm or vascular malformation if the CT is negative but SAH occurred hours earlier (when CT sensitivity begins to decline). 1, 3

Critical Red Flags Present

This patient has multiple features warranting aggressive workup beyond routine migraine evaluation:

• Thunderclap onset (sudden severe headache). 1
• "Worst headache ever" description. 1
• Onset during physical exertion (jogging). 1
• Failure to respond to typical migraine abortive therapy (sumatriptan, NSAIDs). 2, 4
• These features place her outside the typical migraine pattern despite her migraine history. 4

Common Pitfalls to Avoid

• Do not assume this is "just another migraine" based on her history—the atypical features demand investigation for secondary causes. 2, 4
• Do not skip vascular imaging if the initial CT is negative—up to 5.4% of patients with this presentation have aneurysms that require identification. 3
• Do not order MRI first in the emergency setting when SAH is suspected—CT is faster and more sensitive for acute blood. 1, 2
• Do not rely on normal neurological examination to exclude serious pathology—75-80% of posterior circulation strokes lack focal deficits. 1, 4