The Canadian CT Head Rule: A Clinical Decision Tool for Minor Head Injury
The Canadian CT Head Rule is a validated clinical decision tool used to identify patients with minor head injury who require CT scanning, with the goal of reducing unnecessary imaging while ensuring detection of clinically important brain injuries that may require neurosurgical intervention. 1
Patient Selection Criteria
The Canadian CT Head Rule applies to patients with:
- Minor head injury (GCS score 13-15)
- Loss of consciousness, amnesia, or witnessed disorientation
- Injury within the past 24 hours 1
The rule does NOT apply to patients with:
- Unstable vital signs
- Obvious skull fracture
- Seizure
- Coagulopathy or anticoagulant use
- Focal neurologic deficits 1
Risk Factors for CT Scanning
High-Risk Factors (100% sensitive for neurosurgical intervention)
- Failure to reach GCS of 15 within 2 hours of injury
- Suspected open skull fracture
- Any sign of basal skull fracture
- Vomiting more than twice
- Age greater than 65 years 1, 2
Medium-Risk Factors (increase sensitivity for clinically important brain injury)
- Amnesia before impact >30 minutes
- Dangerous mechanism of injury (e.g., pedestrian struck by vehicle, ejection from vehicle, fall from >3 feet or 5 stairs) 1, 2
Comparison with New Orleans Criteria
Both the Canadian CT Head Rule and the New Orleans Criteria have been validated as 100% sensitive for detecting injuries requiring neurosurgical intervention, but they differ significantly in specificity:
- Canadian CT Head Rule: Higher specificity (37.2%-39.7%), potentially reducing CT use by approximately 37% 3, 4
- New Orleans Criteria: Lower specificity (3.0%-5.6%), potentially reducing CT use by only about 3% 3, 4
The New Orleans Criteria includes: headache, vomiting, age >60 years, drug or alcohol intoxication, deficits in short-term memory, physical evidence of trauma above the clavicles, and seizure 5.
Application in Minimal Head Injury
Research has shown that the Canadian CT Head Rule can also be applied to patients with minimal head injury (those without loss of consciousness or disorientation):
- In a study of patients with minimal head injury, the rule was 100% sensitive for detecting intracranial hemorrhage
- The specificity was 29% in this population
- The risk of clinically significant intracranial hemorrhage in minimal head injury patients is very low (2.1% in the study) 6
Clinical Implementation Considerations
- The American College of Emergency Physicians recommends a balanced approach, using the New Orleans Criteria for patients with loss of consciousness or post-traumatic amnesia, and the Canadian CT Head Rule criteria for patients with minimal head trauma 3
- Physician barriers to implementation include concerns about reassurance (both self and patient), patient expectations, and legal liability 6
- Shared decision-making was used in 51% of cases in one study and may be an important approach when applying these rules 6
Pitfalls and Caveats
- Neither rule applies to patients on anticoagulants, who typically require CT scanning regardless of other criteria 1
- The rules were developed for adults and should not be applied to pediatric populations
- While the Canadian CT Head Rule is highly sensitive for detecting injuries requiring neurosurgical intervention, it has lower sensitivity (83.4%-87.2%) for detecting all traumatic CT findings compared to the New Orleans Criteria (97.7%-99.4%) 4
- Clinical judgment should still be exercised, particularly in high-risk populations or when multiple risk factors are present