When to Order CT Scan for Headache
CT head without contrast is recommended for patients with headache when red flag features are present, including abnormal neurological examination, thunderclap onset, progressive worsening, new onset in patients ≥50 years, or headache worsened by Valsalva maneuver. 1
Emergency Indications Requiring Immediate CT
Thunderclap headache (sudden severe onset) requires non-contrast head CT as the first-line test due to superior sensitivity for detecting subarachnoid hemorrhage, with 98.7% sensitivity when performed within 6 hours of symptom onset. 1, 2
Acute presentations warranting immediate CT include:
- Suspected subarachnoid hemorrhage with sudden severe headache 2
- Altered mental status or seizures 3
- Any focal neurological deficits 1
- Signs of increased intracranial pressure 3
Red Flag Features Requiring CT Imaging
Clinical history red flags that warrant CT scanning include:
- New-onset headache in patients ≥50 years old 1
- Progressively worsening headache over days to weeks 1
- Headache worsened by Valsalva maneuver 1
- Headache that awakens patient from sleep 1
- Any unexplained abnormal neurological examination finding 1
Pediatric-specific red flags include:
- Occipital headache location (rare in children and warrants diagnostic caution) 4, 3
- Papilledema on fundoscopic examination 3
- Progressive neurological symptoms 3
- History of sickle cell anemia (lower threshold for imaging due to higher risk of acute CNS events) 4
When CT is NOT Recommended
For typical migraine with normal neurological examination, CT scanning has extremely low yield with only 0.2% prevalence of significant intracranial abnormality. 1 Reflexively ordering imaging on every migraine patient should be avoided, as testing should not be performed if it won't lead to management changes. 1
In young children (ages 2-5) with headache and normal neurological examination, CT scans seldom contribute to diagnosis or immediate management, with one study showing 94% of scans did not contribute to diagnosis or management. 5
Imaging Modality Selection
CT without contrast is the preferred emergency modality because:
- Fast acquisition time critical in emergency settings 1
- Excellent for detecting hemorrhage, mass effect, and hydrocephalus 1
- Decreased safety screening requirements compared to MRI 1
No data supports routine use of CT with contrast for migraine evaluation. 1 Contrast-enhanced CT should only be considered if specific clinical concern exists for progression of intracranial infection, tumor, or inflammatory conditions. 1
MRI is preferred over CT for non-emergent evaluation of suspected tumor, stroke, or other structural lesions, with superior sensitivity for parenchymal abnormalities. 4, 3
Follow-up After Negative CT
If CT is negative but clinical suspicion for subarachnoid hemorrhage remains high (especially >6 hours from onset), lumbar puncture for xanthochromia evaluation should follow. 2 CT sensitivity for SAH decreases significantly after 6 hours from symptom onset. 2
CTA may be warranted after initial CT in select cases:
- High suspicion for arterial dissection 4
- Suspected venous sinus thrombosis (though MRV is preferred in children) 4
- Patients with history of unruptured intracranial aneurysm or cerebral venous thrombosis presenting with new severe headache 6
Common Pitfalls to Avoid
Do not order imaging reflexively without red flags, as the yield is <1% in patients with normal examination and typical primary headache features. 1, 3
Do not skip fundoscopic examination before deciding against imaging, as papilledema indicating increased intracranial pressure may be the only abnormal finding. 3
Do not delay CT if MRI is unavailable when acute stroke or hemorrhage is suspected—CT should not be delayed if MRI is not feasible. 4
Avoid testing if it will not change management, and testing is not recommended if the patient is not significantly more likely than the general population to have a significant abnormality. 1