Red flags for secondary headache
Imaging is indicated when a feature of the history or exam moves the differential away from a primary headache disorder. The acronyms vary, but the substance is similar across guidelines.
- Sudden, severe (thunderclap) onset — emergent evaluation, not outpatient imaging.
- New or progressively worsening headache, especially over weeks.
- Focal neurologic deficit, papilloedema, or altered mental status.
- Headache triggered or worsened by Valsalva, cough, exertion, or recumbency.
- New headache in a patient over 50, or under 5.
- History of malignancy, HIV, or immunosuppression with new headache.
- Fever, meningismus, or systemic signs suggesting infection.
When imaging is not indicated
Patients with a long-standing pattern consistent with migraine or tension-type headache, a normal neurologic exam, and no red flags do not benefit from routine imaging. Imaging in this population yields a high rate of incidental findings without changing management.
Choosing CT vs MRI
Non-contrast head CT is the right first study when acute intracranial haemorrhage, acute trauma, or hydrocephalus is the primary concern, or when MRI is contraindicated. It is fast, widely available, and excellent for acute blood and bony detail.
MRI brain is more sensitive for tumours, demyelination, posterior-fossa pathology, and small infarcts, and is the preferred outpatient study for sub-acute or chronic headache evaluation. Contrast is added when an enhancing mass, leptomeningeal disease, or infection is in the differential.
Special situations
For suspected stroke, see the dedicated stroke / TIA guide — that workflow is its own pathway. For post-traumatic headache after recent injury, non-contrast head CT is the initial test; MRI is added when symptoms persist or when there is concern for diffuse axonal injury, contusion evolution, or chronic post-concussive findings.
Ordering with Precise
Brain MRI and head CT are available across the network with neuroradiology sub-specialty reads. Critical findings are phoned to the ordering provider within 30 minutes of read completion.
Questions referring offices ask first.
Do I need MRI for a typical migraine?
No. A stable migraine pattern with a normal exam and no red flags does not require imaging.
CT or MRI for new headache over 50?
MRI brain is the preferred outpatient study unless an acute haemorrhage is suspected, in which case the patient belongs in the emergency department for a non-contrast head CT.
Should I add contrast?
Add contrast when a mass, infection, or leptomeningeal process is in the differential, or for any patient with known/suspected malignancy or immunocompromise.
Educational reference for referring providers. Not a substitute for clinical judgement or the current official appropriateness criteria. References imaging modalities offered by Precise; modalities not in our network are out of scope.