Most patients with headache have a normal brain MRI or CT, but imaging is often requested to rule out secondary causes. In migraine, subtle findings can sometimes be seen, and advanced MRI techniques help in research and differential diagnosis.
📌 When to Image in Headache? (Red Flags)
Neuroimaging is indicated if:
- First or worst headache (“thunderclap headache”)
- Sudden change in pattern or severity
- Neurological deficits (focal weakness, seizures, altered sensorium)
- Abnormal exam findings (papilledema, cranial nerve palsy)
- Headache in elderly, immunocompromised, or with cancer history
🧾 Primary vs Secondary Headache – Imaging Clues
| Type | Imaging Findings | Key Points |
|---|---|---|
| Migraine | Usually normal MRI/CT; may show small punctate T2/FLAIR hyperintensities in subcortical/deep white matter (frontal lobes). Perfusion MRI: transient hypoperfusion during aura. | White matter lesions more common in migraine with aura. No mass effect/enhancement. |
| Tension Headache | Normal imaging. | No structural abnormality. Diagnosis is clinical. |
| Cluster / Trigeminal Autonomic Cephalalgia | Usually normal MRI. Imaging done to exclude pituitary/cavernous sinus/posterior fossa lesions. | Rule out secondary mimics. |
| Subarachnoid Hemorrhage (SAH) | CT: hyperdensity in sulci, basal cisterns. MRI FLAIR/SWI: sulcal hyperintensity/hemosiderin. | CTA/MRA to detect aneurysm/AVM. |
| Cerebral Venous Thrombosis (CVT) | MRV/CTV: absent venous flow, “empty delta sign.” Parenchymal hemorrhagic infarcts possible. | Consider in young females, postpartum, hypercoagulable states. |
| Idiopathic Intracranial Hypertension (IIH) | MRI: empty sella, dilated optic nerve sheath, posterior scleral flattening, venous sinus stenosis. | Often in obese young women. |
| Reversible Cerebral Vasoconstriction Syndrome (RCVS) | CTA/MRA: “string of beads” appearance from multifocal vasoconstriction. | Associated with thunderclap headaches. |
| Intracranial Mass / Abscess | CT/MRI: space-occupying lesion with mass effect, edema, possible ring enhancement. | Must be excluded in progressive headache with focal deficits. |
📌 Teaching Pearl
- Primary headaches (migraine, tension, cluster) → usually normal imaging, or minimal nonspecific findings.
- Secondary headaches → show structural/vascular abnormalities that guide treatment.
🔍 Imaging in Migraine
Conventional MRI/CT
- Usually normal.
- Rare findings:
- Small, punctate T2/FLAIR hyperintensities in subcortical/deep white matter (especially frontal lobes). More common in migraine with aura.
- No mass effect or enhancement.
Advanced MRI
- Perfusion MRI: Shows transient cortical hypoperfusion during aura.
- MR Angiography (MRA): Reversible narrowing/dilatation of cerebral arteries in migraine variants.
- fMRI: Abnormal activation in visual cortex, brainstem (research setting).
- DTI (Diffusion Tensor Imaging): Subtle white matter microstructural changes reported.
📌 Imaging in Other Primary Headaches
- Tension-type headache: Normal imaging.
- Cluster headache / Trigeminal autonomic cephalalgias:
- Usually normal MRI.
- Rule out secondary causes in cavernous sinus, pituitary, or posterior fossa.
📌 Differential Diagnosis to Exclude on Imaging
- Subarachnoid hemorrhage (CT best in first 24h)
- Intracranial mass/abscess
- Cerebral venous thrombosis (MRV/CTV)
- Idiopathic intracranial hypertension (empty sella, dilated optic nerve sheath, venous sinus stenosis)
- Reversible cerebral vasoconstriction syndrome (RCVS) – “string of beads” on CTA/MRA
📌 Teaching Pearls
- Migraine MRI is usually normal, but small white matter hyperintensities may be seen.
- Always evaluate for secondary causes if red flags are present.
- MRA/MRV are useful in headaches with vascular suspicion.
- CTA/MRA is essential for thunderclap headache (exclude aneurysm/SAH/RCVS).
