NEXUS Head CT Instrument

Why did you develop the NEXUS Head CT Instrument? Was there a particular clinical experience or patient encounter that inspired you to create this tool for clinicians?

We developed the NEXUS Head CT instrument to provide clinicians with a single highly reliable tool they could use to make imaging decisions for all blunt head injury patients. Prior rules, such as PECARN or CHALICE, applied only to specific subgroups of patients, while the inclusion and exclusion criteria of other rules, such as the Canadian Head CT Rule, preclude their application in over one-third of blunt head injury cases. We also wanted to address methodological concerns that validation of these earlier rules had been inadequate, with lower confidence intervals for sensitivity falling below 90%, leaving significant potential for serious missed injuries.

In addition, we wanted to take advantage of the fact that physicians are already very good at identifying and imaging patients with significant injuries (sensitivity approaching 100%), with research showing their performance equals or exceeds existing tools in identifying patients who require imaging. Decision tools provide little benefit, and in some cases because of their impaired sensitivity, could actually prove harmful if used indiscriminately to identify patients who need imaging. On the other hand, physicians frequently order imaging for patients who do not have injuries (physicians exhibit poor specificity) and could benefit from a rule that improves specificity by identifying patients who do not have injuries and who could safely be excluded from imaging. To this end we developed the NEXUS Head CT Instrument as a “one-way” rule that helps clinicians identify blunt head imaging patients who do not require CT imaging. In clinical application, the NEXUS Instrument should be applied whenever Head CT imaging is being considered in the evaluation of a blunt head injured patient. Low-risk classification would indicate that imaging could be safely omitted, while imaging would proceed for all other cases.

What tips do you have for users of this tool? Do you know of cases when it has been applied, interpreted, or used inappropriately?

The optimal use of the tool requires clinicians to conduct an initial evaluation and decide if imaging might be useful. The decision tool should then be applied to determine whether imaging might be safely omitted through “low-risk” classification. While the NEXUS Head CT tool can be used as a two-way tool, and specifically used to determine who needs imaging, its sensitivity of 100% is no better than the 100% sensitivity of clinical judgment (NEXUS, like other decision tools, provides no improvement over clinical judgment in detecting injuries) but could generate false positive results that would in turn increase unnecessary imaging.

It is also important to note that NEXUS classification relies on careful assessments of all of the component criteria. Low risk classification is specifically precluded in cases where one or more of the criteria cannot be completely assessed and documented as low risk.

What recommendations do you have for doctors once they have applied the NEXUS Head CT Instrument? Are there any adjustments or updates you would make to the score based on new data or practice changes?

Head CT imaging decisions are only a part of the evaluation of blunt head injury patients. Brain injuries can sometimes evolve and initially inconsequential injuries can become significant over time. Physicians need to provide appropriate counseling to all of their patients (whether imaged or not) along with adequate return instructions.

CT imaging tools such as the NEXUS Head CT instrument provide limited information on concussions and post concussive syndromes. Low risk classification and negative imaging do not preclude concussive injuries that can result in long-term brain injury and impairment. Again, physicians need to provide appropriate counseling to their patients along with appropriate follow up care.

Do you use this tool in your own clinical practice? Can you give an example of a scenario in which you use it?

Patients with minor head injuries frequently request CT brain imaging. A careful evaluation of the patient, in conjunction with an informative discussion on the manifestations of brain injury and the risks of imaging (primarily lethal malignancy from radiation exposure) can typically resolve most patients’ concerns. I employ the NEXUS rule in cases where I truly have concerns about potential injuries, and unless the rule provides a low risk classification, I proceed with imaging.

Any other research in the pipeline that you’re particularly excited about?

We are currently in the process of developing a NEXUS tool to guide abdominal/pelvic imaging of blunt trauma patients. Upon the completion of this project we will have completed the development of tools to guide core (head, neck, chest, abdomen and pelvis) CT imaging of blunt trauma patients. We are also focusing on ways to exploit artificial intelligence and neural networks to provide the next generation of clinical decision support tools.

William R. Mower, MD, PhD, is a physician at the UCLA Emergency Medical Center. He is also a professor of medicine at the University of California Geffen School of Medicine. Dr. Mower’s primary research is focused on computed tomography and diagnostic radiology.