What is the preferred imaging study, MRI (Magnetic Resonance Imaging) or CT (Computed Tomography) scan, for a patient presenting with severe headaches at the frontal and occipital regions of the head?

Imaging for Severe Frontal and Occipital Headache

For severe headache involving frontal and occipital regions, the choice between MRI and CT depends critically on the clinical context: CT without contrast is preferred for acute presentations requiring emergency evaluation (especially suspected hemorrhage), while MRI without contrast is the superior choice for non-emergent evaluation when structural pathology, tumor, or posterior fossa lesions are suspected. 1, 2

Emergency vs. Non-Emergency Presentation

Acute/Emergency Setting: CT is Preferred

• CT without contrast should be performed first in acute severe headache presentations because it is faster, more readily available, and superior for detecting acute hemorrhage with 98% sensitivity and 99% specificity 3, 2, 4
• CT is the cornerstone for diagnosing subarachnoid hemorrhage (SAH), which must be excluded urgently in severe acute headache 2
• If CT is negative but clinical suspicion remains high, CTA should follow immediately to evaluate for aneurysms or vascular abnormalities 2

Non-Emergency/Outpatient Setting: MRI is Preferred

• MRI without contrast is the imaging modality of choice when there are signs of increased intracranial pressure or concern for tumor 3, 1
• MRI reveals more details of intracranial structures without radiation and is better able to evaluate for meningeal infiltration and isodense tumors compared to CT 3
• MRI is superior for detecting parenchymal abnormalities, infarction, and structural lesions 3

Special Consideration for Occipital Headache

Occipital headache location specifically warrants heightened diagnostic caution and favors MRI evaluation 3:

• Occipital headache is rare and calls for diagnostic caution, as it is not characteristic of primary headache syndromes 3
• MRI is the study of choice for suspected Chiari I malformation, which commonly presents with occipital headache worsened by Valsalva maneuver 3
• MRI should include sagittal T2-weighted sequences of the cranio-cervical junction to evaluate for cerebellar tonsillar herniation 3

Red Flags Requiring Imaging

Neuroimaging should be performed when any of the following features are present 1:

• Headache worsened by Valsalva maneuver
• Headache that awakens the patient from sleep
• New-onset headache in older patients
• Progressively worsening headache over weeks
• Rapid increase in headache frequency
• Abnormal neurological examination findings 1, 5

MRI Protocol Recommendations

When MRI is indicated, the following sequences should be obtained 1:

• T1-weighted sequences
• T2-weighted sequences
• FLAIR sequences
• Diffusion-weighted imaging for stroke evaluation
• Contrast is generally not needed for initial headache evaluation unless specific pathology is suspected 6

Critical Pitfalls to Avoid

• Do not assume severe headache is "just migraine" without proper evaluation, especially with occipital location or red flag features 2
• Do not order MRI in acute settings when CT would be more appropriate for detecting acute hemorrhage 1, 4
• Do not skip vascular imaging (CTA or MRA) if initial CT is negative but clinical suspicion for vascular pathology remains high 2
• Recognize that routine imaging has very low yield (0.2-0.4%) in patients with typical migraine features and completely normal neurological examination 1