Indications for Cranial CT Scan After Head Trauma
Non-contrast head CT is indicated in head trauma patients based on validated clinical decision rules that stratify risk according to presence of loss of consciousness (LOC) or post-traumatic amnesia (PTA), combined with specific clinical features. 1
Algorithm for CT Decision-Making
The 2021 ACR Appropriateness Criteria, incorporating the 2008 ACEP Clinical Policy, provides the most current evidence-based framework 1:
For Patients WITH LOC or PTA (Level A Recommendation)
Obtain non-contrast head CT if any one or more of the following are present:
- Headache
- Vomiting
- Age >60 years
- Drug or alcohol intoxication
- Deficits in short-term memory
- Physical evidence of trauma above the clavicle
- Post-traumatic seizure
- GCS score <15
- Focal neurologic deficit
- Coagulopathy (including anticoagulant medications like warfarin)
For Patients WITHOUT LOC or PTA (Level B Recommendation)
Consider non-contrast head CT if any of the following are present:
- 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 motor vehicle, pedestrian struck by vehicle, fall from height >3 feet or 5 stairs)
Clinical Context and Nuances
This approach balances the highly sensitive New Orleans Criteria (97.7-99.4% sensitivity) for patients with LOC/PTA against the more specific Canadian CT Head Rule (37.2-39.7% specificity) for minimal trauma without LOC/PTA 1. Both rules have been validated as essentially 100% sensitive for detecting mild head trauma requiring neurosurgical intervention 1.
Important caveat: These guidelines apply to patients ≥16 years of age. Pediatric head trauma requires different criteria 1.
Coagulopathy Considerations
While most guidelines recommend CT for all head trauma patients with coagulopathy, recent evidence suggests this may be overly broad 2. However, the current standard remains to image these patients given the potential for delayed hemorrhage, though controversy exists regarding antiplatelet therapy alone in minimal trauma 1.
Moderate to Severe Trauma
For moderate (GCS 9-12) or severe (GCS 3-8) head trauma, non-contrast head CT is always appropriate and should be performed immediately 1. Clinical decision rules are unnecessary in these populations.
Common Pitfalls to Avoid
- Do not use skull radiographs - they have been replaced by CT, which is far more sensitive for neurosurgical lesions 1
- Do not routinely use MRI for initial evaluation - it has no role in acute head trauma imaging 1
- Do not perform CTA, MRA, or advanced imaging unless there is specific suspicion for vascular injury 1
- Avoid imaging patients with truly minimal trauma who meet none of the above criteria - the yield is extremely low (approximately 2% abnormality rate) 3
Recent research confirms that headache, LOC/amnesia, and alcohol intoxication are the strongest predictors of abnormal CT findings 4, while GCS <15, somnolence, and clinical signs of fracture also significantly increase risk 5.