When is a computed tomography (CT) scan of the brain indicated for a patient presenting with headache?

When to Perform CT Brain for Headache

CT brain imaging for headache is indicated primarily for patients with red flag symptoms, including thunderclap headache, abnormal neurological signs, new onset headache in patients over 50, immunocompromised state, or when there is suspicion of subarachnoid hemorrhage, mass lesion, or increased intracranial pressure. 1, 2

Red Flags Requiring Immediate CT Brain Imaging

• Thunderclap headache (sudden severe headache reaching maximum intensity within seconds to minutes) - requires immediate non-contrast CT to evaluate for subarachnoid hemorrhage 1, 2
• Abnormal neurological examination findings 1, 2
• Persistent vomiting with headache 2
• Headache onset before age 6 2
• Progressive or worsening pattern of headache 2
• Positional headache (may suggest intracranial hypotension or mass) 2
• Immunocompromised state 2
• History of cancer (risk of metastasis) 2
• Pregnancy with atypical headache features 2
• Anticoagulant use or coagulopathy (increased risk of intracranial bleeding) 1
• Hypertensive emergency 1
• Suspicion of intracranial infection 1

Specific Clinical Scenarios for CT Brain

1. Suspected Subarachnoid Hemorrhage

• Non-contrast CT is the imaging modality of choice for detecting acute subarachnoid hemorrhage with 98% sensitivity and 99% specificity 1, 3
• If performed within 6 hours of headache onset, a negative CT interpreted by experienced neuroradiologists may be sufficient to rule out SAH without requiring lumbar puncture 3
• For patients presenting >6 hours after onset, CSF analysis is still indicated even with negative CT 3

2. Suspected Vascular Abnormalities

• If initial non-contrast CT shows subarachnoid or parenchymal hemorrhage, further evaluation with CT angiography (CTA) is indicated to assess for aneurysm or arteriovenous malformation 1
• CTA can detect unruptured intracranial aneurysms with high sensitivity (97.9%) 4, 5

3. Suspected Venous Sinus Thrombosis

• If MRV is not possible or results are ambiguous, contrast-enhanced CT venography (CTV) is a fast alternative with high sensitivity for detecting venous sinus thrombosis 1
• However, MRV is generally preferred over CTV due to radiation concerns 1

4. Prior to Lumbar Puncture

• CT is sometimes performed in the acute setting of suspected intracranial infection before lumbar puncture to help determine if it is safe to perform the procedure (by excluding mass lesions or cerebral edema producing midline shift or herniation) 1

When CT Brain is NOT Indicated

• Typical primary headache disorders (migraine, tension-type) with normal neurological examination and no red flags 2
• Chronic or recurrent headaches with stable pattern and no new features 2
• Sinusitis-related headache (CT findings of chronic sinusitis occur with similar frequency in patients with and without headache) 6

MRI vs CT for Headache Evaluation

• MRI without contrast is the preferred initial imaging modality for non-emergency headache evaluation 2
• CT is appropriate as initial test in emergency settings where rapid assessment is needed 2
• The yield of neuroimaging in primary headache disorders without red flags is extremely low (approximately 1 clinically significant abnormality per 61 scans) 2

Important Caveats

• Overimaging patients with typical headache patterns and normal neurological examination can lead to detection of incidental findings that cause unnecessary anxiety and further testing 2
• CT has limited sensitivity for posterior fossa lesions, small brain tumors, and early ischemic changes 1
• When evaluating pediatric patients, MRI is generally preferred over CT due to radiation concerns, though CT may be necessary in emergency situations 1

By following these evidence-based guidelines, clinicians can appropriately utilize CT brain imaging for headache evaluation while avoiding unnecessary radiation exposure and healthcare costs.