CT Head Injury Decision Rule
Canadian CT Head Rule: Determine need for head CT in minor head injury. Reduce unnecessary radiation in African emergency departments.
The Canadian CT Head Rule (CCHR) is a validated clinical decision rule that identifies which adults with minor head injury require CT imaging, safely reducing unnecessary scans and radiation exposure. It applies to patients with a witnessed loss of consciousness, amnesia, or disorientation and an initial GCS of 13-15. Its high sensitivity for clinically important brain injury and need for neurosurgical intervention makes it especially valuable in resource-limited emergency departments.
🧮 Interactive Calculator
📐 Formula
High risk: GCS <15 at 2hr, suspected open/depressed skull fracture, signs of basal skull fracture, ≥2 vomiting episodes, age ≥65. Medium risk: amnesia >30min, dangerous mechanism
Reference: Stiell et al., Lancet 2001
When to Use
- Minor head injury in adults with GCS 13-15 and witnessed loss of consciousness, amnesia, or confusion
- Blunt trauma presenting within 24 hours of injury
- Emergency departments seeking to limit CT use and radiation in low-risk patients
- Triage of head-injured patients where CT access is limited and must be prioritised
How It Works
- The rule uses five high-risk and two medium-risk criteria; presence of any one triggers the corresponding recommendation.
- High-risk criteria (predict need for neurosurgical intervention): GCS <15 at 2 hours post-injury, suspected open or depressed skull fracture, any sign of basal skull fracture (haemotympanum, raccoon eyes, CSF oto/rhinorrhoea, Battle's sign), two or more episodes of vomiting, and age 65 years or older.
- Medium-risk criteria (predict clinically important CT findings): retrograde amnesia of 30 minutes or more before impact, and a dangerous mechanism (pedestrian struck, occupant ejected, fall from >3 feet or 5 stairs).
- The rule is applied only after excluding patients outside its derivation set (see limitations).
- No arithmetic score is produced; it is a Boolean any-positive-criterion decision aid.
Interpreting the Result
- Any high-risk criterion present: perform CT head; these patients are at risk of injury requiring neurosurgical intervention.
- Any medium-risk criterion present (with no high-risk feature): perform CT head to detect clinically important brain injury, though neurosurgery is unlikely.
- No criteria present: CT can be safely omitted with very low risk of missing important injury (sensitivity approaching 100% for neurosurgical lesions).
- The rule identifies the need for imaging, not a probability; a negative rule supports observation and discharge with head-injury advice.
- Clinical judgement overrides the rule when other concerning features (e.g. coagulopathy, focal deficit) are present.
Limitations & Pitfalls
- Validated only for minor head injury with GCS 13-15; not for GCS <13 or moderate/severe injury.
- Excludes patients under 16, those on anticoagulants or with bleeding disorders, obvious open skull fracture, seizure after injury, and no clear history of LOC/amnesia/disorientation.
- Does not apply to pregnancy or to unstable vital signs.
- Anticoagulated and antiplatelet patients were excluded from derivation, so the rule cannot reassure that group; many guidelines mandate CT for them regardless.
- Interobserver assessment of criteria such as dangerous mechanism can vary.
- It predicts intracranial injury, not extracranial trauma, and should not replace overall trauma assessment.
References
- Stiell IG et al. The Canadian CT Head Rule for patients with minor head injury. Lancet. 2001.
- Stiell IG et al. Comparison of the Canadian CT Head Rule and the New Orleans Criteria. JAMA. 2005.
- NICE Guideline NG232: Head injury: assessment and early management. 2023.
- Easter JS et al. Comparison of clinical decision rules for CT in minor head injury. Ann Emerg Med. 2015.
⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.