Best Imaging Modality Following Head Trauma
Noncontrast head CT is the gold standard and only appropriate initial imaging modality for acute head trauma in adults aged 16 years and older. 1, 2
Why CT is the Clear Choice
CT has revolutionized head trauma management since the 1970s by rapidly detecting neurosurgical emergencies—hemorrhage, herniation, and hydrocephalus—that require immediate intervention to prevent secondary injury and death. 1, 2 The speed and sensitivity of CT for acute hemorrhage make it irreplaceable in the emergency setting, where minutes matter for patient survival. 2, 3
Modalities That Should NOT Be Used Initially
The American College of Radiology explicitly states there is no relevant literature supporting the following for initial evaluation of acute head trauma: 1
- MRI (too slow, patient often too unstable) 1, 2
- MR angiography (MRA) 1
- CT angiography (CTA) (unless vascular injury suspected) 1
- Skull radiographs (replaced by CT, which is far more sensitive) 1
- PET/CT 1
- MR spectroscopy 1
- Functional MRI 1
- Diffusion tensor imaging (DTI) 1
- Catheter angiography 1
When to Order CT: Clinical Decision Rules
Not every head trauma requires imaging. Use validated clinical decision rules to determine who needs CT scanning, as only 10% or less of mild head trauma shows positive findings on CT, and only 1% or less requires neurosurgical intervention. 1
For Patients WITH Loss of Consciousness (LOC) or Post-Traumatic Amnesia (PTA):
Level A Recommendation: Order noncontrast head CT if ANY of the following are present: 1, 4
- Headache
- Vomiting
- Age >60 years
- Drug or alcohol intoxication
- Short-term memory deficits
- Physical evidence of trauma above the clavicle
- Post-traumatic seizure
- GCS score <15
- Focal neurologic deficit
- Coagulopathy
For Patients WITHOUT LOC or PTA:
Level B Recommendation: Consider noncontrast head CT if ANY of the following are present: 1, 4
- Focal neurologic deficit
- Vomiting
- Severe headache
- Age ≥65 years
- Physical signs of basilar skull fracture
- GCS score <15
- Coagulopathy
- Dangerous mechanism of injury (ejection from vehicle, pedestrian struck, fall >3 feet or 5 stairs)
For Moderate to Severe Head Trauma:
Always order noncontrast head CT immediately for: 2, 4, 5
- Moderate head trauma (GCS 9-12)
- Severe head trauma (GCS 3-8)
- Progressive neurologic deterioration
- Declining GCS (e.g., from 15 to ≤8)
Technical Considerations
Multiplanar reformatted images should be included with head CT as they increase diagnostic accuracy. 1 Review both bone and brain windows systematically to optimize detection of fractures, hemorrhage, mass effect, and signs of increased intracranial pressure. 3
Critical Pitfalls to Avoid
Never delay CT imaging for "medical stabilization" in acute trauma—this worsens outcomes. 2 Time is brain tissue when intracranial hemorrhage or herniation is present.
Never order MRI first in acute trauma with declining mental status—it wastes precious time that could be used for life-saving intervention. 2 While MRI is more sensitive for subtle parenchymal injury and diffuse axonal injury, this advantage is meaningless if the patient herniates while waiting 45 minutes for an MRI scan. 6, 7
Do not attribute declining consciousness to drugs, alcohol, or metabolic causes when clear trauma history with high-risk features exists—get the CT first. 2
Remember that patients on anticoagulants require imaging even with minimal trauma due to coagulopathy risk. 5
Role of MRI (Not Initial, But Has a Place)
MRI becomes appropriate only after initial CT evaluation in specific scenarios: 1, 4, 6
- Subacute to chronic head trauma with persistent symptoms
- When CT findings don't adequately explain the clinical picture
- Follow-up imaging (MRI is more sensitive for parenchymal changes than repeat CT)
- Suspected diffuse axonal injury after negative or minimally positive CT
For follow-up and chronic symptoms, MRI is superior to CT for detecting subtle white matter lesions and parenchymal changes. 4, 6, 7