External validation of computed tomography decision rules for minor head injury: prospective, multicentre cohort study in the NetherlandsBMJ 2018; 362 doi: https://doi.org/10.1136/bmj.k3527 (Published 24 August 2018) Cite this as: BMJ 2018;362:k3527
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Re: External validation of computed tomography decision rules for minor head injury: prospective, multicentre cohort study in the Netherlands
Foks et al have made a significant contribution to understanding the accuracy of four decision rules commonly used to identify conscious patients with head injury who should have a CT scan because of their risk of intracranial complications. Based on the data on the sensitivity and specificity of each of the four rules in identifying patients with a brain injury detected radiologically, they recommend wider adoption of the CT in Head Injury Patient (CHIP) rule. Before the CHIP replaces existing guidelines based on the Canadian CT Head Rule, however, such as the NICE head injury guideline, we think that two limitations of the study need to be further considered.
The first is the use of radiological (CT) outcome measures. The clinical significance of brain injuries identified radiologically in patients with differing characteristics is not well established. In our recent systematic review, the majority of initially conscious (Glasgow Coma Scale 13-15) patients with injuries identified by CT imaging do not have clinically significant sequelae. The risk of adverse outcomes including neurosurgery and death is determined not only by the nature of the injury identified but also patient factors. The Canadian CT Head Rule derivation study measured neurosurgery or death, which represents a more clinically useful outcome. As the acuity of CT imaging increases the use of any radiologically identified injury as a primary outcome in such research may mean that studies are assessing an ever-more frequent outcome that has a diminishing relationship to clinically important end points. It would be useful if the researchers could report how accurately the various rules identified patients who subsequently underwent neurosurgery or died.
The second concern we have is the implication that the only important trade-off is between the number of unnecessary CT scans performed on conscious patients with head trauma (specificity) against the number of clinically significant injuries that a clinician is prepared to risk missing (sensitivity). The use of a more sensitive rule with a lower specificity increases the rate of imaging and, therefore the radiological identification of more injuries that have uncertain clinical significance in alert patients. These diagnoses increase radiation exposure in young people, may lead to unnecessary patient concern and costly hospital admissions solely for observation.[3 4] Ongoing prognostic studies that aim to better risk stratify conscious patients with injuries identified by CT imaging will improve the understanding of the clinical consequences and costs of these different imaging strategies. These studies will also inform appropriate further management once an injury is identified.[5 6]
The CHIP rule, as the authors suggest, may be the best available. However, it needs further assessment of its performance in relation to clinical and health economic outcome measures before it replaces Canadian CT Head based rules.
1. Foks KA, van den Brand CL, Lingsma HF, et al. External validation of computed tomography decision rules for minor head injury: prospective, multicentre cohort study in the Netherlands. BMJ 2018;362:k3527. doi: 10.1136/bmj.k3527 [published Online First: 2018/08/26]
2. Marincowitz C, Lecky FE, Townend W, et al. The Risk of Deterioration in GCS13-15 Patients with Traumatic Brain Injury Identified by Computed Tomography Imaging: A Systematic Review and Meta-Analysis. J Neurotrauma 2018;35(5):703-18. doi: 10.1089/neu.2017.5259 [published Online First: 2018/01/13]
3. Goodacre S. Hospital admissions with head injury following publication of NICE guidance. Emerg Med J 2008;25(9):556-7. doi: 10.1136/emj.2007.055723
4. Marincowitz C, Lecky FE, Allgar, et al. The impact of the SIGN head injury guidelines and NHS 4-hour Emergency Target on hospital admissions for head injury in Scotland: An Interrupted Times Series. BMJ Open Under Review
5. Marincowitz C, Lecky FE, Townend W, et al. A protocol for the development of a prediction model in mild traumatic brain injury with CT scan abnormality: which patients are safe for discharge? Diagnostic and Prognostic Research 2018;2(1):6. doi: 10.1186/s41512-018-0027-4
6. Maas AI, Menon DK, Steyerberg EW, et al. Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI): a prospective longitudinal observational study. Neurosurgery 2015;76(1):67-80. doi: 10.1227/NEU.0000000000000575
Competing interests: No competing interests