When to perform a computed tomography (CT) scan in a 35-year-old woman with persistent headache one month after a concussion?

CT Scan for Persistent Headache One Month After Concussion

Brain MRI is the recommended imaging modality for a 35-year-old woman with persistent headache one month after concussion, not a CT scan. 1

Rationale for Imaging Selection

Acute vs. Subacute/Chronic Phase Considerations

• In acute head trauma (0-7 days), CT is the preferred initial imaging modality due to its speed and sensitivity for detecting acute hemorrhage and neurosurgical emergencies 1
• For subacute/chronic head trauma (>7 days, including at one month post-injury), MRI becomes the preferred imaging modality 1

Why MRI is Superior at One Month Post-Concussion

• MRI is more sensitive than CT for detecting:

  • Subtle findings adjacent to the calvarium or skull base
  • Focal encephalomalacia (from previous contusions)
  • Small white matter lesions/microbleeds from traumatic axonal injury
  • Diffuse axonal injury (DAI) that may explain persistent cognitive or neurologic deficits 1

• Only 10% of diffuse axonal injuries are detectable on CT, as >80% of lesions are not associated with macroscopic hemorrhage 1

When CT Might Still Be Appropriate at One Month

CT remains a valid option in specific scenarios:

• When there is a specific question not requiring high soft-tissue contrast resolution 1
• For patients presenting with gradual decline after trauma (e.g., due to subacute/chronic subdural hematoma) 1
• When MRI is contraindicated (e.g., non-MRI compatible implants, severe claustrophobia)

Clinical Context of Persistent Post-Concussive Symptoms

• Persistent neurocognitive/postconcussive symptoms affect approximately 58% of patients at 1 month after mild TBI 1
• Headache is a common post-concussive symptom that may persist despite normal imaging
• If initial CT was normal in the acute phase but symptoms persist, MRI may reveal abnormalities in approximately 27% of patients 1

Special Considerations

• If the patient is on anticoagulant therapy, they are at higher risk for delayed intracranial complications, which may warrant different management 2
• If there are new or worsening neurological symptoms beyond just headache, urgent imaging may be indicated

Algorithm for Decision-Making

1. Determine if this is the first imaging study since the concussion

   • If no prior imaging was done, MRI is preferred at one month
   • If prior CT was normal but symptoms persist, MRI is indicated
   • If prior CT showed abnormalities, follow-up MRI is recommended

2. Assess for red flags requiring urgent evaluation:

   • New focal neurological deficits
   • Worsening or progressive symptoms
   • Seizures (highly predictive of intracranial abnormality) 3
   • Use of anticoagulants 2

In conclusion, at one month post-concussion with persistent headache, brain MRI is the appropriate imaging modality of choice rather than CT scan, as it offers superior sensitivity for detecting subtle abnormalities that may explain persistent symptoms.