What are the indications for a CT (Computed Tomography) scan after a head injury with loss of consciousness?

Indications for CT Scan After Head Injury with Loss of Consciousness

A CT scan is indicated after head injury with loss of consciousness when patients meet criteria from validated clinical decision rules such as the Canadian CT Head Rule, New Orleans Criteria, or NICE guidelines, as these identify patients at risk for intracranial injury requiring intervention. 1

Major Clinical Decision Rules for CT Scanning After Head Trauma

Canadian CT Head Rule (for GCS 13-15 with blunt trauma)

• Loss of consciousness 1
• GCS score <15 at 2 hours after trauma 1
• Suspected skull base fracture 1
• Vomiting (≥2 episodes) 1
• Age >65 years 1
• Dangerous mechanism of injury 1

New Orleans Criteria (for GCS 15 only)

• Headache 1
• Vomiting 1
• Age >60 years 1
• Drug or alcohol intoxication 1
• Persistent anterograde amnesia 1
• Evidence of trauma above the clavicles 1
• Seizure 1

NICE Guidelines

• GCS <15 at initial assessment 1
• Suspected skull fracture 1
• Any sign of basal skull fracture 1
• Post-traumatic seizure 1
• Focal neurological deficit 1
• More than one episode of vomiting 1
• Amnesia for events >30 minutes before impact 1
• Age ≥65 years 1
• Coagulopathy (including anticoagulant use) 1
• Dangerous mechanism of injury 1

Additional High-Risk Factors Warranting CT Scan

• Duration since injury >12 hours with symptoms 2
• Nausea and vomiting (significantly associated with abnormal CT findings) 3, 2
• Signs of head trauma (significantly associated with abnormal CT findings) 3
• Neurological deterioration after initial assessment 1
• Persistent neurologic deficits unexplained by initial examination 1
• Anticoagulation therapy (especially with initial CT abnormalities) 1

Special Considerations

• Patients with GCS 15 and no symptoms after loss of consciousness have approximately 3% risk of abnormal CT findings 3
• Elderly patients (>60 years) have higher risk of intracranial injury even with minimal symptoms 4
• Patients with occipital or non-frontal impact locations have higher risk of intracranial lesions 4
• Pedestrians in motor vehicle accidents, falls from height, and high-velocity mechanisms carry higher risk 4

Follow-up Imaging Considerations

• Routine repeat CT is not recommended for mild TBI with negative initial CT (class III recommendation) 1
• Follow-up CT is indicated for:
  • Any neurological deterioration (class I recommendation) 1
  • Moderate to severe TBI (evidence level II) 1
  • Anticoagulated patients with abnormalities on initial CT 1

When MRI May Be Indicated Instead of CT

• When CT is normal but persistent unexplained neurological deficits exist 1
• For detection of subtle findings adjacent to calvarium or skull base 1
• For evaluation of small white matter lesions in suspected traumatic axonal injury 1
• Note: MRI is not recommended as initial imaging in acute head trauma (class IIb recommendation) 1

Common Pitfalls to Avoid

• Relying solely on GCS score without considering other risk factors 1
• Discharging patients without proper written instructions about warning signs 1
• Failing to recognize that normal CT does not exclude all traumatic brain injuries, particularly non-hemorrhagic axonal injury 1
• Overuse of repeat CT scanning in mild TBI with negative initial CT and no neurological deterioration 1

By following these evidence-based guidelines, clinicians can appropriately identify patients who require CT scanning after head injury with loss of consciousness while avoiding unnecessary imaging in low-risk cases.