Journal Club: The Canadian Head CT Rule

The purpose of Journal Club is to review papers essential to emergency medicine. The aim is not to summarize the latest and most up-to-date literature recently released. Instead, Journal Club will review the methodology, data, and conclusions of landmark papers which are used in a day to day basis in modern Emergency Medicine. Oftentimes, the conclusions of these studies are used in treatment decisions, but the basics of the studies are not as well known by clinicians.

The Canadian Head CT Rule

The Canadian Head CT Rule is used in day to day practice in the emergency room. The paper was first published in 2001 by Stiell et al in The Lancet and sets down a clinical decision rule for use of CT scans in minor head traumas.

The Rule
In head trauma patients with GCS = 13-15 who lost consciousness, have amnesia to the trauma, or are confused upon initial presentation, a head CT is not necessary if all of the following criteria are negative:

• GCS < 15 at 2 hours after the trauma
• Suspected open or depressed skull fracture
• Signs of basilar skull fracture i.e. hemotympanum, raccoon eyes, Battle’s sign, or otorrhea/rhinorrhea consisting of CSF
• 2 or more episodes of vomiting
• Age > 65
• Retrograde amnesia > 30 minutes to the event
• Dangerous mechanism

If the patient meets any of these criteria, he or she needs a head CT

Study Question

• In patients suffering minor head trauma, which ones need a CT scan of their brain?

Study Design

• Prospective cohort study
• 10 large Canadian hospitals
• Outcome: need for neurological intervention OR clinically important brain injury on CT
• Number of patients: 3121
• Common misconception: this rule doesn’t apply to head trauma patients who are at baseline, have no amnesia, and didn’t lose consciousness

Study Population

• Inclusion criteria:
  • Blunt head trauma causing witnessed loss of consciousness, definite amnesia, or witnessed disorientation
  • GCS of 13-15 upon initial presentation
  • Head injury in the last 24 hours
• Exclusion criteria:
  • < 16 years old
  • Minimal head injury (no LOC, amnesia, or disorientation)
  • No clear history of trauma as the primary event
  • Penetrating skull injury or obvious depressed skull fracture
  • Acute focal neurological deficit
  • Unstable vital signs
  • Seizure before assessment in the ER
  • Bleeding disorder or on anticoagulation
  • Patient who returns to the ER for the same head injury
  • Pregnant patients

Outcomes

• Primary outcome: need for neurosurgical intervention. This is defined as:
  • death within 7 days secondary to head injury
  • need for craniotomy
  • elevation of depressed skull fracture
  • intracranial pressure monitoring
  • intubation for head injury shown on CT
• Secondary outcome: clinically important brain injury on CT requiring hospital admission and neurological followup
  • All brain injuries found on CT were included In this group UNLESS the patient was neurologically intact and had one of the following minor injuries
    • solitary contusion < 5mm in diameter
    • localized subarachnoid hemorrhage less than 1mm thick
    • smear subdural hematoma < 4mm thick
    • isolated pneumocephaly
    • closed depressed skull fracture not through the inner table
  • This definition was standardized after surveys were given to 129 neurosurgeons, neuroradiologists, and ER physicians

Method

• Enrolled patients were low risk head trauma patients as defined above who were evaluated by a clinician trained to identify 22 different criteria which were being studied.
• Enrolled patients either had a head CT (if the ER physician felt it was indicated) OR had a telephone followup 14 days later. Patients were classified as either:
  • Having a need for neurosurgical intervention or clinically important brain injury on CT (as defined above)
  • OR as having a clinically insignificant or no brain injury
    • These patients either had a negative head CT OR met all of the following criteria in their telephone interview 14 days later
      • Mild or absent headache
      • No memory or concentration problems
      • No seizure or focal motor neurological findings
      • Return to daily activities
      • Error score < 10 out of 28 on the Katzman Short Orientation-Memory-Concentration-Test
    • Patient who failed the 14 day telephone interview were recalled to the hospital for a head CT
    • If the followup head CT was negative, the patient was classified as having a clinically insignificant injury

Results

• Study population: 3121
• CT scans: 2078
• Two week follow up interview: 1043
• 363 patients were excluded because they did not have a CT scan and were lost to followup
• Patients requiring neurological intervention: 44
• Clinically important brain injury: 254
• Clinically unimportant lesion (as defined above): 94

Analyses

• Each of the patients were evaluated by trained ER physicians for 24 primary predictor variables.
• Logistic regression and recursive partitioning analyses were used to analyze the data
• The analyses identified 5 high risk criteria and 2 medium risk criteria. When the high risk criteria were combined, one could identify all of the patients who were at risk for requiring neurological intervention. When the medium risk criteria were added, one could additionally identify patients who were at risk for having clinically important lesions

Conclusions

• Patients who meet any of the high risk criteria are at risk for requiring neurological intervention.
• Patients who meet the medium risk criteria are at risk for having clinically important lesions.