The Canadian CT Head Rule [Classics Series]

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1. The Canadian CT Head Rule consists of 7 predictor variables to assess the need for CT imaging in patients with minor head injuries.

2. This study demonstrates that the rule is highly sensitive and may help to reduce the number of CT scans ordered.

Study Rundown: The Canadian CT Head Rule was developed in this prospective cohort study. It is a highly sensitive clinical decision rule for patients with minor head injuries and has helped standardize the management of these patients. Moreover, these findings suggest that the Rule can help to reduce the number of CT scans ordered in assessing patients with minor head injuries.

In sum, the Canadian CT Head Rule is a clinical decision rule to standardize the management of patients presenting to the emergency department with minor head injury.

Please click to read study in The Lancet

In Depth [prospective cohort study]: First published in The Lancet in 2001, the Canadian CT Head Rule was designed to identify patients who required computed tomography (CT) after suffering minor head injuries. The definition of a minor head injury is a history of loss of consciousness, amnesia, or disorientation and a Glasgow Coma Scale (GCS) score of 13-15. At the time, there were conflicting guidelines regarding the use of CT in patients suffering these injuries, and the Canadian CT Head Rule sought to standardize the management of patients while reducing the number of unnecessary CT scans. This prospective cohort study was carried out in 10 Canadian community and academic centres. The primary outcome was the need for neurological intervention (i.e., death within 7 days due to head injury, or need for craniotomy, elevation of skull fracture, intracranial pressure monitoring, or intubation for head injury within 7 days), while the secondary outcome was the presence of clinically important brain injury identified on CT.

Patients requiring a CT were identified by standardized physician assessments, which included assessing for pre-determined predictor variables. Patients not requiring a CT were followed-up with a phone call 14 days after their assessment. A total of 3,121 patients were enrolled, and 2,078 of these patients received CT scans. Logistic regression was carried out to develop a model for identifying cases with clinically important brain injury, and the model was used to generate the 7 predictors in the Canadian CT Head Rule.

Canadian CT Head Rule
CT head is only required for minor head injury patients with any of these findings:
High risk (for neurological intervention)
  1. GCS score <15 at 2 hours after injury
  2. Suspected open or depressed skull fracture
  3. Any sign of basal skull fracture (i.e., hemotympanum, “racoon” eyes, CSF otorrhea/rinorrhea, Battle’s sign)
  4. Vomiting ≥2 episodes
  5. Age ≥65 years
Medium risk (for brain injury on CT)
  1. Amnesia before impact ≥30 minutes
  2. Dangerous mechanism (i.e., pedestrian struck by motor vehicle, occupant ejected from motor vehicle, fall from elevation ≥3 feet/5 stairs)

Subsequent analyses demonstrated that the 5 high risk factors had a sensitivity of 100% (95% CI 92-100%) and specificity of 68.7% (95% CI 67-70%) for neurological intervention, while CT scans would have been ordered in 32.2% of patients. When all 7 factors were considered, the sensitivity was 98.4% (95% CI 96-99%) and specificity was 49.6% (95% CI 48-51%) for clinically important brain injury on CT, while CT scans would have been ordered in 54.3% of patients.

By Adrienne Cheung, Andrew Cheung, M.D.

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