When to order a computed tomography (CT) scan in patients with a chief complaint (c/o) of head trauma according to the Canadian CT Head Rule?

Canadian CT Head Rule for Head Trauma

According to the Canadian CT Head Rule, a CT scan is indicated in patients with head trauma who have a GCS score of 13-15 and any one of the following high-risk criteria: GCS <15 at 2 hours post-injury, suspected open or depressed skull fracture, signs of basilar skull fracture, vomiting ≥2 episodes, age ≥65 years, amnesia >30 minutes before impact, or dangerous mechanism of injury. 1

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

• GCS score <15 at 2 hours after injury 1
• Suspected open or depressed skull fracture 1
• Any sign of basilar skull fracture (hemotympanum, raccoon eyes, Battle's sign, CSF otorrhea/rhinorrhea) 1
• Vomiting ≥2 episodes 1
• Age ≥65 years 1, 2

Medium-Risk Criteria (for brain injury detection)

• Amnesia before impact >30 minutes 1
• Dangerous mechanism of injury (pedestrian struck by vehicle, occupant ejected from vehicle, fall from height >3 feet or 5 stairs) 1, 3

Important Clinical Considerations

• The Canadian CT Head Rule was originally developed for patients with GCS 13-15 with witnessed loss of consciousness, amnesia, or disorientation 1
• The rule has been validated to be 100% sensitive for detecting injuries requiring neurosurgical intervention 4, 5
• While the New Orleans Criteria has higher sensitivity for detecting any traumatic brain injury (97.7%-99.4%), the Canadian CT Head Rule offers better specificity (37.2%-39.7% vs 3.0%-5.6%) 1, 5
• The Canadian CT Head Rule could potentially reduce CT scan usage by approximately 37%, while the New Orleans Criteria would only reduce scans by about 3% 1, 5

Special Populations

Patients with Minimal Head Injury (no LOC or disorientation)

• The Canadian CT Head Rule has been validated in patients with minimal head injury (no loss of consciousness or disorientation) with 100% sensitivity and 29% specificity for detecting intracranial hemorrhage 6
• Risk of clinically significant injury in minimal head trauma patients is very low 6

Anticoagulated Patients

• Both the Canadian CT Head Rule and American College of Emergency Physicians guidelines recommend CT for all patients with coagulopathy (including those on anticoagulant medications) regardless of other criteria 1, 7
• Anticoagulated patients have a significantly higher risk of intracranial hemorrhage (3.9%) compared to non-anticoagulated patients (1.5%) 7

Algorithmic Approach

1. Assess GCS score (must be 13-15 to apply the rule) 1
2. Check for high-risk criteria (requires immediate CT if any present) 1
3. Check for medium-risk criteria (consider CT if any present) 1
4. For patients on anticoagulants, proceed directly to CT regardless of other criteria 7
5. For elderly patients (≥65 years), maintain a lower threshold for CT as age is a strong independent predictor of intracranial injury 3, 2

Comparative Performance

• In validation studies, the Canadian CT Head Rule demonstrated 100% sensitivity for neurosurgical intervention with specificity of 60-76% 4
• The Canadian CT Head Rule showed better performance than the New Orleans Criteria in a Japanese tertiary referral hospital study 8
• An Austrian trial found that the Canadian CT Head Rule detected the need for neurosurgical intervention with 80% sensitivity and 72% specificity 2

Remember that while the Canadian CT Head Rule is highly sensitive for detecting injuries requiring neurosurgical intervention, it has lower sensitivity (83.4%-87.2%) for detecting all traumatic intracranial findings 1, 5. Clinical judgment should supplement the rule, especially in high-risk populations like the elderly and those on anticoagulants.