What is the Canadian CT (Computed Tomography) Head Rule?

The Canadian CT Head Rule

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 the potential to reduce CT use by approximately 37% while maintaining 100% sensitivity for detecting injuries requiring neurosurgical intervention. 1

Definition and Criteria

The CCHR consists of five high-risk factors and two medium-risk factors that help clinicians determine which patients with minor head injury should undergo CT scanning:

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

• Failure to reach a Glasgow Coma Scale (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 Factors (for detecting clinically important brain injury)

• Amnesia before impact greater than 30 minutes
• Dangerous mechanism of injury 1, 2

Application and Performance

The CCHR was originally developed for patients with a GCS score of 13-15 who had experienced loss of consciousness, amnesia, or witnessed disorientation. When applied to this population, the CCHR demonstrates:

• 100% sensitivity (95% CI 92-100%) for predicting need for neurosurgical intervention
• 98.4% sensitivity (95% CI 96-99%) for detecting clinically important brain injury
• Potential to reduce CT scanning by approximately 37% 2

More recent validation studies have confirmed these findings, with the CCHR maintaining 100% sensitivity for detecting injuries requiring neurosurgical intervention across multiple studies 3, 4.

Comparison with Other Decision Rules

When compared to the New Orleans Criteria (NOC), the CCHR demonstrates:

• Equal sensitivity (100%) for detecting injuries requiring neurosurgical intervention
• Lower sensitivity (83.4%-87.2% vs. 97.7%-99.4%) for detecting all neurocranial traumatic findings
• Significantly higher specificity (37.2%-39.7% vs. 3.0%-5.6%)
• Greater potential for reducing unnecessary CT scans (37.3% vs. 3.0%) 4

This makes the CCHR particularly valuable in resource-constrained settings where minimizing unnecessary imaging is important.

Extended Applications

While originally developed for patients with GCS 13-15 who had loss of consciousness or disorientation, research has shown that the CCHR can also be applied to:

1. Patients with minimal head injury (no loss of consciousness or disorientation)

   • Maintains 100% sensitivity for detecting intracranial hemorrhage
   • May help reduce unnecessary CT scanning in this low-risk population 5

2. Elderly patients from residential care facilities

   • Implementation of the CCHR reduced CT brain scans by 20% without missing clinically significant injuries
   • No adverse outcomes were observed when the rule was applied in this population 6

Clinical Implementation Considerations

When implementing the CCHR in clinical practice, consider these important points:

• The rule should be applied only to patients with blunt trauma to the head resulting in witnessed loss of consciousness, definite amnesia, or witnessed disorientation
• Patients should have a GCS score of 13-15 upon assessment in the emergency department
• The rule is not applicable to patients:
  • Under 16 years old
  • On anticoagulants or with bleeding disorders
  • With obvious open skull fractures
  • With focal neurological deficits
  • With seizure prior to emergency department assessment
  • Returning for reassessment of the same head injury 1, 2

Clinical judgment should still be exercised, particularly in high-risk populations or when multiple risk factors are present, even when the CCHR suggests CT may not be necessary.

By applying the CCHR appropriately, clinicians can ensure that patients who need neuroimaging receive it while reducing unnecessary CT scans, radiation exposure, and healthcare costs.