What is the Canadian Head Computed Tomography (CT) rule for minor head injury?

The Canadian CT Head Rule for Minor Head Injury

The Canadian CT Head Rule (CCHR) is a highly sensitive clinical decision tool that identifies patients with minor head injury who require CT scanning, with 100% sensitivity for detecting injuries requiring neurosurgical intervention while allowing for a potential reduction in CT use by approximately 37%. 1

Criteria for Application

The CCHR applies to patients with:

• Minor head injury (GCS 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 after injury
• Coagulopathy or anticoagulant use
• Focal neurologic deficits
• Age under 16 years 1

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

CT scan is recommended for patients with any of these five high-risk factors:

1. Failure to reach GCS of 15 within 2 hours of injury
2. Suspected open skull fracture
3. Any sign of basal skull fracture
4. Vomiting more than twice
5. Age greater than 65 years 1, 2

Medium-Risk Criteria

Additional factors that increase risk of clinically important brain injury:

1. Amnesia before impact >30 minutes
2. Dangerous mechanism of injury (e.g., pedestrian struck by vehicle, ejection from vehicle, fall from height >3 feet or 5 stairs) 1, 2

The combination of high and medium-risk factors is 98.4% sensitive for predicting clinically important brain injury 2.

Comparison with Other Decision Rules

The CCHR has been compared to other clinical decision rules, most notably the New Orleans Criteria (NOC):

• Sensitivity: Both rules are 100% sensitive for detecting injuries requiring neurosurgical intervention 3
• Specificity: CCHR has higher specificity (37.2%-39.7%) compared to NOC (3.0%-5.6%) 3
• CT Reduction: CCHR could potentially reduce CT use by approximately 37%, while NOC would only reduce CT use by about 3% 4, 3

Evidence for Expanded Use

The CCHR has been evaluated in patients with minimal head injury (no loss of consciousness or disorientation):

• In a study of 240 patients with minimal head injury, the CCHR was 100% sensitive for detecting intracranial hemorrhage 5
• All cases of intracranial hemorrhage occurred in patients who met either high-risk criteria (age) or medium-risk criteria (mechanism) 5
• No patients with intracranial hemorrhage required ICU care or intervention 5

Implementation Considerations

When implementing the CCHR in clinical practice:

• The rule was developed and validated in adult populations and should not be applied to pediatric patients 1
• Patients on anticoagulants typically require CT scanning regardless of other criteria 1
• Clinical judgment should still be exercised, particularly with high-risk populations or when multiple risk factors are present 1

Common Pitfalls

• Applying the rule to patients who don't meet inclusion criteria (e.g., pediatric patients, patients on anticoagulants)
• Failing to recognize signs of basal skull fracture (e.g., hemotympanum, raccoon eyes, Battle's sign, CSF otorrhea/rhinorrhea)
• Not waiting the full 2 hours to assess for return to normal GCS when applicable
• Underestimating the significance of vomiting (must be >2 episodes)
• Overlooking dangerous mechanisms of injury when taking history

The CCHR provides an evidence-based approach to determining the need for CT scanning in patients with minor head injury, balancing the need to identify clinically significant injuries while reducing unnecessary imaging.