Head CT for New Onset Headaches in Adults
For an adult with new onset headaches and no red flag features, neuroimaging is generally not indicated; however, when imaging is warranted based on clinical red flags, a noncontrast head CT is the appropriate first-line modality.
Clinical Decision Framework
The decision to image depends entirely on the presence or absence of "red flag" features that suggest serious underlying pathology 1:
Red Flags Requiring Imaging 1
- Age ≥50 years - significantly increases risk of serious pathology 2
- Sudden severe onset ("thunderclap" or "worst headache of life") - concern for subarachnoid hemorrhage 1, 3
- Focal neurologic deficits - suggests structural lesion 4
- Altered mental status or cognitive changes - warrants immediate evaluation 4
- Immunocompromised state or active cancer - higher risk of infection or metastases 1
- Recent head trauma - even minor trauma in older patients 2
- Headache associated with activity, position, or Valsalva - concern for mass effect or increased intracranial pressure 1
- Progressive worsening pattern - suggests evolving pathology 1
- Pregnancy - unique considerations for secondary causes 1
Imaging Modality: Noncontrast Head CT
When imaging is indicated, CT head without IV contrast is the appropriate initial study 4. This recommendation is based on several key factors:
- Speed and availability - can be completed within minutes in emergency settings 5, 6
- High sensitivity for acute hemorrhage - the most critical time-sensitive diagnosis to exclude 6, 3
- Detects neurosurgical emergencies - including hemorrhage, herniation, hydrocephalus, and mass effect 5
- Universal availability - present in all emergency departments 5
Why Contrast is NOT Needed Initially
IV contrast administration is not indicated for initial evaluation of new onset headache 4, 6. The evidence shows:
- No relevant literature supports routine use of contrast CT for headache evaluation 4
- Contrast delays diagnosis and is unnecessary for detecting the most critical pathology (hemorrhage) 6
- Contrast is only considered after hemorrhage is excluded, for specific suspected diagnoses like venous thrombosis or vascular malformations 6
Special Clinical Scenarios
Thunderclap Headache (Sudden Severe Onset)
For patients presenting with sudden severe headache peaking within one hour:
- Noncontrast CT has 100% sensitivity when performed within 6 hours of onset 3
- Modern third-generation CT identifies all cases of subarachnoid hemorrhage when interpreted by a qualified radiologist within this timeframe 3
- CT angiography (CTA) may be considered after negative noncontrast CT to exclude aneurysm with >99% posttest probability, potentially avoiding lumbar puncture 7
Known Migraineurs
Even migraineurs reporting "worst headache of life" have extremely low yield on CT scanning (0% critical findings) when they lack other red flags such as cancer, immunocompromise, intracranial pathology, or recent trauma 8. The value of scanning these patients is questionable 8.
Common Pitfalls to Avoid
Misattribution of Symptoms
- Do not assume chronic sinusitis findings on CT explain acute headache - these findings occur with equal frequency (17-22%) in headache patients and controls, suggesting they are incidental 9
- Do not delay imaging when red flags are present - waiting for "medical stabilization" when intracranial hemorrhage is suspected can worsen outcomes 5, 6
Inappropriate Imaging Choices
- Never order MRI as the initial test in acute presentations with potential hemorrhage - it takes too long and patients may be too unstable 5, 6
- Do not routinely add contrast to every headache CT - the number needed to scan to find clinically significant abnormality is prohibitively high 6
Clinical Assessment Errors
- Do not attribute declining consciousness to other causes (drugs, metabolic disorders) when clear red flag features are present 5
- Do not assume nosebleed with headache is purely local ENT problem - may indicate hypertensive emergency, coagulopathy, or intracranial pathology requiring CT 6
When Imaging is NOT Required
For patients with new onset headache without red flags - particularly young patients with typical migraine or tension-type features, normal neurologic examination, and no concerning historical features - neuroimaging is not indicated 1. The vast majority of headaches are benign and idiopathic, resolving spontaneously or with minor therapeutic measures 1.
Post-Imaging Management
If CT is negative but headaches persist or worsen, monitor for red flag symptoms including progressive worsening, new focal deficits, altered mental status, severe refractory pain, or orthostatic features 2. In such cases, repeat neuroimaging with MRI is preferred over repeat CT 2.