What is the Canadian Head CT (Computed Tomography) rule, including its sensitivity and specificity for determining the need for a head CT scan in patients with minor head injuries?

The Canadian CT Head Rule for Minor Head Injury

The Canadian CT Head Rule is a highly sensitive clinical decision tool for determining the need for head CT in patients with minor head injury, with 100% sensitivity for detecting injuries requiring neurosurgical intervention while maintaining a specificity of 37.2%-39.7%, allowing for a potential reduction in CT use by approximately 37%. 1, 2

Components of the Canadian CT Head Rule

High-Risk Criteria (100% sensitive for neurosurgical intervention)

• Failure to reach GCS score 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

Medium-Risk Criteria (98.4% sensitive for clinically important brain injury)

• Amnesia before impact >30 minutes
• Dangerous mechanism of injury (e.g., ejection from vehicle, pedestrian struck by vehicle, fall from >3 feet or 5 stairs)

Sensitivity and Specificity

The Canadian CT Head Rule has been extensively validated in multiple studies:

• For neurosurgical intervention: 100% sensitivity (95% CI 64.6%-100%) 3
• For any traumatic brain injury: 83.4%-87.2% sensitivity 1, 3
• For specificity: 37.2%-39.7%, significantly higher than the New Orleans Criteria (3.0%-5.6%) 1, 3

When compared to the New Orleans Criteria in head-to-head studies:

• Both rules are 100% sensitive for detecting injuries requiring neurosurgical intervention
• The Canadian CT Head Rule has lower sensitivity but much higher specificity for detecting any intracranial injury
• The Canadian CT Head Rule could potentially reduce CT use by approximately 37% compared to only 3% with the New Orleans Criteria 1, 3

Application to Minimal Head Injury

While originally developed for patients with GCS 13-15 with loss of consciousness or witnessed disorientation, the Canadian CT Head Rule has also been validated in patients with minimal head injury (no loss of consciousness):

• In a study of patients with minimal head injury, the Canadian CT Head Rule maintained 100% sensitivity (95% CI 40%-100%) for detecting intracranial hemorrhage
• Specificity was 29% (95% CI 23%-35%) in this population 4

Patient Selection Criteria

The Canadian CT Head Rule was designed for patients with:

• Minor head injury (GCS 13-15)
• Loss of consciousness, amnesia, or witnessed disorientation
• Injury within the past 24 hours 2

Important Exclusions

The rule does not apply to patients with:

• Unstable vital signs
• Obvious skull fracture
• Seizure after injury
• Coagulopathy or anticoagulant use
• Focal neurologic deficits
• Age under 16 years 1, 2

Clinical Implementation

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
• Using the Canadian CT Head Rule for patients with minimal head trauma without loss of consciousness 1

This approach maximizes sensitivity while maintaining reasonable specificity to reduce unnecessary CT scans.

Pitfalls and Caveats

• Clinical judgment should still be exercised, particularly with high-risk populations
• The rule was developed for adults and should not be applied to pediatric populations
• Patients on anticoagulants typically require CT scanning regardless of other criteria 2
• Physician comfort with not ordering CT scans may be influenced by factors such as reassurance (both physician and patient), patient expectations, and medicolegal concerns 4

The Canadian CT Head Rule represents a well-validated approach to reducing unnecessary CT scans while maintaining excellent sensitivity for clinically significant injuries requiring intervention.