Should a CT scan for a patient with headaches be ordered with or without contrast?

CT Scan for Headache Evaluation: With or Without Contrast

For patients with headaches, a non-contrast CT scan should be ordered as the initial imaging study, with contrast added only when specific indications are present.

Initial Imaging Approach

Non-contrast head CT is the first-line neuroimaging test of choice for headache evaluation and can be performed safely and rapidly in all patients 1. This approach is supported by multiple guidelines:

• The American College of Radiology (ACR) recommends non-contrast head CT as the initial imaging modality for headache evaluation 1, 2
• Non-contrast CT is particularly valuable for detecting acute conditions like subarachnoid hemorrhage, with 98% sensitivity and 99% specificity 2
• For suspected head trauma with headache, non-contrast CT is the standard initial imaging approach 1

When to Add Contrast

Contrast should be added only in specific circumstances:

• When abnormalities are found on the initial non-contrast scan
• When there is suspicion of infection
• When there is concern for mass lesion
• When inflammatory conditions are suspected 2

The use of contrast-enhanced head CT as a first-line test in acute headache settings does not add significant value over non-contrast examinations 1.

Decision Algorithm for Headache Imaging

1. For acute severe headache with normal neurological exam:

   • Begin with non-contrast head CT
   • If normal and high suspicion for subarachnoid hemorrhage remains, consider lumbar puncture 3
   • CT angiography may be considered if vascular abnormalities are suspected 4, 5

2. For chronic headache with normal neurological exam:

   • Non-contrast MRI is preferred over CT if available 2
   • The yield of neuroimaging in primary headache disorders without red flags is extremely low (number needed to scan: 61) 4
   • CT without contrast is appropriate if MRI is unavailable or contraindicated

3. For headache with red flags:

   • Non-contrast CT for initial rapid assessment
   • Add contrast only if initial findings suggest need for enhanced imaging
   • Red flags include: thunderclap headache, abnormal neurological signs, new onset headache in patients over 50, immunocompromised state, or when there is suspicion of mass lesion 2

Important Considerations

• CT has limited sensitivity for posterior fossa lesions, small brain tumors, and early ischemic changes 2
• The diagnostic yield of CT in patients with chronic headache and normal neurological exam is low (0.9% pre-test probability of significant findings) 6
• Overimaging patients with typical headache patterns can lead to detection of incidental findings (15% of scans) that cause unnecessary anxiety and further testing 2, 7
• For suspected vascular abnormalities after initial non-contrast CT, consider CT angiography rather than adding contrast to the initial scan 2, 5

Special Populations

• For head trauma patients with headache: non-contrast CT is the standard approach 1
• For patients over 50 with new-onset headache: non-contrast CT is appropriate, but also consider temporal arteritis evaluation with ESR and CRP 2
• For suspected CSF leak: non-contrast head CT is the initial imaging of choice 1

Remember that most primary headaches can be diagnosed based on history and examination alone, with minimal reliance on imaging studies. Reserve imaging for patients with concerning features or atypical presentations.