What are the criteria for ordering a computed tomography (CT) scan after head trauma?

CT Criteria After Head Trauma

Use validated clinical decision rules—specifically the Canadian CT Head Rule or New Orleans Criteria—to determine which head trauma patients require CT scanning, rather than imaging all patients or relying on clinical gestalt alone. 1

Severity Classification by Glasgow Coma Scale

Head trauma severity guides imaging decisions and is classified as: 1

• Mild: GCS 13-15 (>75% of all head trauma cases)
• Moderate: GCS 9-12
• Severe: GCS ≤8
• Minimal: GCS 15 without loss of consciousness or amnesia

Canadian CT Head Rule (Preferred for Specificity)

This rule achieves 100% sensitivity for neurosurgical intervention while reducing CT utilization by 37%, making it the most efficient validated tool. 2, 3, 4

High-Risk Criteria (Any ONE requires immediate CT):

• GCS <15 at 2 hours post-injury 2
• Suspected open or depressed skull fracture 2
• Any sign of basilar skull fracture (hemotympanum, raccoon eyes, Battle's sign, CSF otorrhea/rhinorrhea) 2
• Vomiting ≥2 episodes 2
• Age ≥65 years 2, 5

Medium-Risk Criteria (Any ONE requires CT for brain injury detection):

• Amnesia >30 minutes before impact 2
• Dangerous mechanism of injury: pedestrian struck by vehicle, occupant ejected from vehicle, fall from height >3 feet or >5 stairs 2, 6

The high-risk criteria identify 100% of patients requiring neurosurgical intervention and would necessitate CT in only 32% of patients. 3 The medium-risk criteria achieve 98.4% sensitivity for clinically important brain injury with 49.6% specificity, requiring CT in 54% of patients. 3

New Orleans Criteria (Higher Sensitivity, Lower Specificity)

This rule is more sensitive (97.7%-99.4%) but less specific (3.0%-5.6%) than the Canadian CT Head Rule, reducing CT utilization by only 3%. 4 Use when you cannot tolerate missing any traumatic CT finding:

Criteria (Any ONE requires CT):

• Headache 6
• Vomiting 6
• Age >60 years 6
• Drug or alcohol intoxication 6
• Persistent anterograde amnesia (short-term memory deficits) 6
• Physical evidence of trauma above the clavicles 6
• Seizure 6

Mandatory CT Regardless of Clinical Decision Rules

Anticoagulation/Coagulopathy

All patients on anticoagulants (warfarin, DOACs) or with coagulopathy require CT regardless of other criteria. 2, 6 Anticoagulated patients have 3.9% risk of intracranial hemorrhage versus 1.5% in non-anticoagulated patients. 2 There is ongoing controversy about whether antiplatelet therapy alone (aspirin, clopidogrel) mandates CT in minimal trauma, but most guidelines recommend imaging. 1

Moderate-to-Severe Trauma

All patients with GCS ≤12 require immediate CT. 1 These patients have substantially higher rates of positive CT findings and neurosurgical intervention needs.

Focal Neurological Deficits

Any focal neurological signs mandate CT. 6, 5 This includes motor weakness, sensory deficits, cranial nerve abnormalities, or asymmetric reflexes.

When CT Can Be Safely Avoided

CT is not indicated for patients meeting ALL of the following: 6

• GCS 15 maintained throughout evaluation
• No loss of consciousness or amnesia
• No headache or vomiting
• No physical evidence of trauma above clavicles
• Not on anticoagulant therapy
• No dangerous mechanism of injury
• Age <60-65 years

Only 10% of mild head trauma shows positive CT findings, and only 1% requires neurosurgical intervention, justifying selective rather than universal imaging. 1

Special Population Considerations

Elderly Patients (≥65 years)

Age ≥65 is an independent high-risk criterion requiring CT. 2, 5 The Florida Geriatric Head Trauma CT Rule, specifically validated for patients ≥65, assigns points for: arrival via EMS, GCS <15, antiplatelet medications, loss of consciousness, basilar skull fracture signs, and headache, with CT recommended for scores ≥25. 5

Intoxicated Patients

Drug or alcohol intoxication is an indication for CT because reliable neurological examination is impossible and these patients cannot be safely observed. 6

Common Pitfalls to Avoid

• Do not rely on clinical gestalt alone—mathematical models show that clinical decision rules with ≥97% sensitivity outperform both "CT all" and "discharge all" strategies for quality-adjusted life years. 1
• Do not skip CT in elderly patients with "minor" mechanisms—age ≥65 is itself a high-risk criterion regardless of mechanism. 2
• Do not observe anticoagulated patients without imaging—their hemorrhage risk is 2.6-fold higher. 2
• Do not use the Canadian CT Head Rule in patients with GCS <13—it was validated only for GCS 13-15. 3
• Do not delay CT beyond 2 hours in patients with initial GCS <15—the 2-hour reassessment is critical for the Canadian CT Head Rule. 2, 3

Algorithmic Approach

1. Assess GCS score: If ≤12, proceed directly to CT 1
2. Check anticoagulation status: If on anticoagulants, proceed directly to CT 2
3. Apply Canadian CT Head Rule high-risk criteria: If any present, proceed to CT 2
4. Apply Canadian CT Head Rule medium-risk criteria: If any present, proceed to CT 2
5. If all criteria negative: CT not indicated; observe and discharge with head injury precautions 6

Recent data from 2025 shows that 57% of all head CTs and 80.2% of mild trauma CTs are potentially avoidable when guidelines are not followed, emphasizing the importance of adherence to validated decision rules. 7