CDR Blog

The Canadian CT Head Rule (CCHR), created by Stiell et al (2001), was developed to allow clinicians to rule-out intracranial injuries that might require neurosurgical intervention, without the need for a CT Head. If one or more criteria in the rule are present for a given patient, intracranial injury cannot be ruled out and CT head should be considered. Overall, across multiple studies and jurisdictions, this CDR has been found to be 83-100% sensitive for detecting all “clinically important” intracranial injuries, with the high risk criteria being 100% sensitive for injuries requiring neurosurgical intervention (Stiell et al. 2001; Stiell et al. 2005). Application of this CDR has been reported to enable an approximately 35% reduction in CT head imaging (Smits et al. 2005).

The rule was initially derived in a multi-centre prospective cohort study across EDs in 10 Canadian hospitals, with enrollment of 3,121 consecutive adult patients presenting with acute minor head injuries. Patients were assessed for 22 potential predictor variables before completion of CT head imaging. Primary outcome was the need for neurological intervention, and secondary outcome was “clinically important brain injury” on CT. The 22 predictor variables were each independently assessed by univariate analysis, with the strongest variables then assessed in combination via logistic regression or recursive partitioning methods. Five high-risk clinical factors were found to be 100% sensitive (95% CI: 92-100%) and 68.7% specific (95% CI: 67-70%) in predicting the need for neurological intervention, and the authors stated an opinion that CT should be mandatory for patients meeting high-risk criteria. An additional two medium-risk factors were found to be 98.4% sensitive (95% CI: 96-99%) and 49.6% specific (95% CI: 48-51%) in prediction of clinically important brain injuries likely requiring admission but not requiring neurological intervention. Notably, the study excluded key patient populations including: pregnant patients, patients with bleeding disorders, and those on anticoagulation.

Four major validation studies have been performed. Stiell et al (2005) used a convenience sample of 2707 adults presenting with minor head injury (GCS 13-15) across nine Canadian ED’s and demonstrated sensitivity of 100% (95%CI: 91-100%) for neurosurgical intervention, and 100% (95%CI: 98-100%) for “clinically important brain injury”. It was also determined that the CCHR was associated with fewer CT scans ordered than compared to the New Orleans Criteria (NOC): 52.1% vs 88.0% with NOC, p<0.001. Patients also spent ~2.5 fewer hours in the ED when images were not obtained.

Two major studies compared the CCHR to NOC. Smits et al (2005) validated CCHR against NOC in a large, multi-centre prospective validation study. It used a modified CCHR, treating medium-risk and high-risk features as equivalent. It also removed the exclusion criteria, and instead, used them as additional risk factors favouring CT scan. The study determined sensitivity for traumatic lesion to be 83.4% (95%CI: 77.7%-87.9%) for CCHR and 98.3% (95%CI: 94.0%-99.5%) for NOC. These increased slightly when using the modified CCHR. However, both the original and modified CCHR and NOC had sensitivity of 100% for neurosurgical intervention. Importantly, CT reduction was estimated to be 5.3% (95% C.I.: 4.2%-6.6%) for the original NOC, 3.0% (95% C.I.: 2.4%-3.6%) for the modified NOC, 37.1% (95% C.I.: 35.0%-39.2%) for the original CCHR, and 37.3% (95% C.I.: 35.6%-39.0%) for the modified CCHR. Bouida et al (2013) conducted an observational cohort study compared CCHR to NOC in identifying need for neurosurgical intervention, intubation within 15 days, and presence of traumatic lesions on CT. The study enrolled 1582 patients, of whom 1122 received CT scans. CCHR outperformed NOC in both need for neurosurgical intervention and in detecting clinically important injury. For neurosurgical intervention, CCHR had a sensitivity of 100% (95% C.I.: 90-100), a specificity of 60% (95% C.I.: 44% to 76%) and a negative predictive value (NPV) of 100% (95% C.I.: 99% to 100%). Additionally, for clinically significant brain injury, the study found CCHR to have a sensitivity of 95% (95% C.I.: 92% to 98%), a specificity of 65% (95% C.I.: 62% to 68%) and a NPV of 99% (95% C.I.: 98% to 100%).

Finally, a systematic review by Harnan et al determined that both CCHR and NOC had sensitivities of 99-100% for injuries requiring neurosurgical intervention, however NOC had superior sensitivity for intracranial injury than CCHR (95-100% vs 80-100%). While CCHR had lower sensitivity than NOC, it did not miss any clinically significant findings and allowed for greater reduction in CT scans than NOC.

There remains a paucity of studies illustrating impact of CCHR on patient outcomes. Studies conducted in California and Nairobi demonstrated a decrease in the number of CT scans ordered (5.3% and 73.8%, respectively). Stiell et al (2010) conducted a cluster randomized trial, which demonstrated no significant difference in the use of CT imaging with the use of CCHR.

We classified the Canadian CT Head Rule as CDR Level 1. This CDR has undergone prospective validation testing in multiple settings (Canada, USA, UK, Nairobi), and has been the subject of multiple impact studies. While published results on impact have been somewhat variable, multiple studies have shown a reduction in CT imaging rates, which acts as an important indicator of both reduced healthcare spending, and reduced patient time spent in the ED. Additional studies are required to confirm changes in physician behaviour and improved patient outcomes resulting from use of this CDR.

1. Stiell IG, Clement CM, Grimshaw JM, et al. A prospective cluster-randomized trial to implement the Canadian CT Head Rule in emergency departments. CMAJ. 2010;182(14):1527-1532. doi:10.1503/cmaj.091974

2. Stiell IG, Wells GA, Vandemheen K, et al. The Canadian CT Head Rule for patients with minor head injury. The Lancet. 2001;357(9266):1391-1396. doi:10.1016/S0140-6736(00)04561-X

3. Stiell IG, Clement CM, Rowe BH, et al. Comparison of the Canadian CT Head Rule and the New Orleans Criteria in patients with minor head injury. JAMA. 2005;294(12):1511-1518. doi:10.1001/jama.294.12.1511

4. Smits M, Dippel DWJ, de Haan GG, et al. External validation of the Canadian CT Head Rule and the New Orleans Criteria for CT scanning in patients with minor head injury. JAMA. 2005;294(12):1519-1525. doi:10.1001/jama.294.12.1519\

5. McGinn TG, Guyatt GH, Wyer PC, Naylor CD, Stiell IG, Richardson WS. Users’ guides to the medical literature: XXII: how to use articles about clinical decision rules. Evidence-Based Medicine Working Group. JAMA. 2000;284(1):79-84. doi:10.1001/jama.284.1.79

6. Bouida W, Marghli S, Souissi S, et al. Prediction value of the Canadian CT head rule and the New Orleans criteria for positive head CT scan and acute neurosurgical procedures in minor head trauma: a multicenter external validation study. Ann Emerg Med. 2013;61(5):521-527. doi:10.1016/j.annemergmed.2012.07.016

7. Harnan SE, Pickering A, Pandor A, Goodacre SW. Clinical decision rules for adults with minor head injury: a systematic review. J Trauma. 2011;71(1):245-251. doi:10.1097/TA.0b013e31820d090f

8. Sharp AL, Huang BZ, Tang T, et al. Implementation of the Canadian CT Head Rule and Its Association With Use of Computed Tomography Among Patients With Head Injury. Ann Emerg Med. 2018;71(1):54-63.e2. doi:10.1016/j.annemergmed.2017.06.022

9. Abdalla RO, Qureshi MM, Saidi H, Abdallah A. Introduction of the Canadian CT Head Rule Reduces CT Scan Use in Minor Head Injury. Annals of African Surgery. 2015;12(1). doi:10.4314/aas.v12i1.

10. Boyle A, Santarius L, Maimaris C. Evaluation of the impact of the Canadian CT head rule on British practice. Emerg Med J. 2004;21(4):426-428.

11. Schuur JD, Carney DP, Lyn ET, et al. A top-five list for emergency medicine: a pilot project to improve the value of emergency care. JAMA Intern Med. 2014;174(4):509-515. doi:10.1001/jamainternmed.2013.12688

12. Papa L, Stiell IG, Clement CM, et al. Performance of the Canadian CT Head Rule and the New Orleans Criteria for predicting any traumatic intracranial injury on computed tomography in a United States Level I trauma center. Acad Emerg Med. 2012;19(1):2-10. doi:10.1111/j.1553-2712.2011.01247.x

13. Easter JS, Haukoos JS, Claud J, et al. Traumatic intracranial injury in intoxicated patients with minor head trauma. Acad Emerg Med. 2013;20(8):753-760. doi:10.1111/acem.12184