Canadian CT Head Rule

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Stiell IG, et al. "The Canadian CT Head Rule for patients with minor head trauma". The Lancet. 2001. 357(9266):1391-96.
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Clinical Question

Among patients with minor head trauma, is it possible to develop a sensitive and specific tool to determine the necessity of CT head imaging?

Bottom Line

The Canadian CT head rule is a rapid method of determining which patients need CT imaging upon presentation to the emergency department with head trauma.

Major Points

Many experts rely on clinical gestalt to identify patients at high risk who should undergo head CT imaging for trauma. The Canadian rules were designed to identify a set of objective criteria for determining whether trauma patients are likely to require neurological intervention or have clinically important brain injury. The rule identifies two sets of criteria, one for high-risk patients and the other for low-risk patients. The first, a set of high-risk criteria, identifies with 100% sensitivity (95% CI 0.92-1.00) patients at risk for emergent neurological intervention, when any of the following are present:

  1. GCS score <15 at 2h post injury
  2. Suspected open or depressed skull fracture
  3. Any sign of basal skull fracture (raccoon eyes, battles sign, etc.)
  4. >1 episode of emesis
  5. Age ≥64 years

A second group of patients, identified with 95% sensitivity, is at moderate risk; namely, they are at risk of having clinically important brain injury when any of the following are present:

  1. Have amnesia of 30 minutes or greater prior to trauma
  2. Trauma from dangerous mechanism (eg, fall greater than 3 feet, MVA with ejection from vehicle, or pedestrian vs. motor vehicle accident)


  • Prospective cohort derivation study
  • N=3121
  • Setting: 10 Canadian emergency departments
  • Enrollment: 1996-1999


Inclusion Criteria

  • Blunt trauma to the head
  • Witnessed loss of consciousness or disorientation
  • Definite amnesia
  • GCS ≥13 in the ED
  • Injury within 24 hours

Exclusion Criteria

  • Age <16 years
  • Minimal head injury (no loss of consciousness, amnesia, or disorientation)
  • Absence of clear history of trauma as inciting event (eg, syncope or seizure as inciting event)
  • Penetrating skull injury or depressed skull fracture
  • Acute focal neurological deficit
  • Unstable vital signs
  • Seizure prior to ED assessment
  • Bleeding disorder
  • On oral anticoagulation
  • Had returned for reassessment of same head injury
  • Pregnancy

Baseline Characteristics

  • Mean age: 39 years
  • Men: 69%
  • Mean time between injury and physician assessment: 3.1 hours
  • Arrival by ambulance: 73%
  • Transfer from outside hospital: 13%
  • Witnessed loss of consciousness: 46%
  • Amnesia: 87%
  • Initial GCS score:
    • 15: 80%
    • 14: 17%
    • 13: 4%
  • Mechanism of injury:
    • Fall: 31%
    • MVA: 26%
    • Assault: 11%
    • Sports: 10%
    • Bicycle: 7%
    • Pedestrian struck: 6%
    • Head struck/hit by object: 6%
    • Motorcycle: 4%
    • Other: 1%


  • Consecutive patients presenting with head trauma with above inclusion criteria were enrolled
  • All patients were assessed by study investigator using one-hour session to review 22 different clinical features
  • Decision to obtain CT head imaging was made by treating physician (not investigators)
  • All patients received follow-up telephone interview at 14 days, evaluated for memory loss, difficulty concentrating, seizure or other neurological deficits, and a score of ≥10 on Katzman Short Orientation-Memory-Concentration Test. Presence of any of these prompted interviewers to advise a return visit to the ED. Absence of all of these features indicated a lack of clinically important brain injury
  • Patients who received CT head were compared to those who did not
  • Various statistical methods used to determine risk factors for need for neurological intervention and clinically important brain injury


Performance of high-risk decision rule, consisting of 5 criteria.

High risk by decision rule, requiring neurological intervention
Sensitivity 100% (95% CI 0.92-1.00)
Specificity 68.7% (95% CI 0.67-0.70)

Performance of all factors, consisting of 7 criteria.

Moderate risk by decision rule, with clinically important injury
Sensitivity 98.4% (95% CI 0.96-0.99)
Specificity 49.6% (95% CI 0.48-0.51)


  • 363 patients who did not meet CT criteria were not included in the final statistical analysis, because they were lost to follow-up.
  • 1358 patients presented to the study center EDs for minor head trauma, however were not enrolled in the study.
  • The 14-day follow-up telephone interview had not been evaluated for precision/reliability in ruling out clinically relevant brain injury.
  • The Canadian Head CT Rule allows for minor or clinically unimportant brain injury to go unimaged and without hospital admission, which in some countries, like the United States, is considered important and to many clinicians usually necessitates both imaging and admission.


Funding provided by the Medical Research Council of Canada and the Ontario Ministry of Health, Emergency Health Services Committee.