When is a non-contrast vs contrast Computed Tomography (CT) scan recommended for a patient presenting with a headache?

CT for Headache: Non-contrast vs. Contrast Guidelines

For patients presenting with headache, a non-contrast CT scan is recommended as the initial imaging study, with contrast added only when specific indications are present. 1

Initial Imaging Approach

• Non-contrast head CT is the first-line neuroimaging test of choice for headache evaluation 1
• Non-contrast CT can be performed safely and rapidly in all patients presenting with headache
• Non-contrast CT has excellent sensitivity (98%) and specificity (99%) for detecting acute subarachnoid hemorrhage 1

When to Use Non-contrast CT

1. Acute head trauma (mild, moderate, or severe) 2
2. Thunderclap headache to rule out subarachnoid hemorrhage 1, 3
   • Modern CT scanners (16-slice or greater) have 98.7% sensitivity for SAH within 6 hours of headache onset 3
3. Red flag symptoms including:
   • Abnormal neurological signs
   • New onset headache in patients over 50
   • Immunocompromised state
   • Persistent vomiting
   • Headache onset before age 6
   • Progressive or worsening pattern of headache
   • Positional headache
   • History of cancer
   • Pregnancy with atypical headache features 1

When to Add Contrast

Contrast should be added to CT only in specific circumstances:

1. Abnormalities found on initial non-contrast scan requiring further characterization 1
2. Suspicion of infection (meningitis, encephalitis, abscess)
3. Concern for mass lesion requiring better delineation
4. Suspected inflammatory conditions 1

Special Imaging Considerations

• CT Angiography (CTA) should be considered for:

  • Suspected vascular abnormalities
  • Suspected arterial dissection
  • Evaluation after negative non-contrast CT in thunderclap headache 4, 5
  • Research shows CTA can detect aneurysms with 97.9% sensitivity 4

• MR Venography (MRV) may be appropriate for:

  • Suspected cerebral venous thrombosis 1
  • Studies show 3% of patients with acute severe headache may have CVT 5

Important Caveats and Pitfalls

1. False negatives can occur:

   • CT has limited sensitivity for posterior fossa lesions and small brain tumors 1
   • Anemia may reduce sensitivity of CT for subarachnoid hemorrhage 6
   • Consider lumbar puncture if clinical suspicion remains high despite negative CT

2. Repeat imaging considerations:

   • Repeat non-contrast head CTs with the same clinical indication have significantly lower yield (1.8%) compared to first-time scans (4.3%) 7
   • New or different symptoms warrant new imaging despite prior negative scans

3. Overimaging risks:

   • Routine neuroimaging for typical headache patterns with normal neurological examination can lead to detection of incidental findings
   • These incidental findings may cause unnecessary anxiety and further testing 1

4. When to consider MRI instead:

   • MRI without contrast is preferred for subacute or chronic head trauma with unexplained cognitive or neurological deficits 2
   • MRI is more sensitive for posterior fossa lesions

By following these evidence-based guidelines, clinicians can optimize the use of CT imaging for headache evaluation, ensuring appropriate use of contrast when indicated while minimizing unnecessary radiation and contrast exposure.