Date: September 30th, 2014
Guest Skeptic: Dr. Marcel Emond. Associate professor, Laval University. Emergency physician the level one trauma centre in Quebec City. Research Director of the Canadian Emergency Team Initiative (CETI).
Case: 21-year-old man loses control of his snowmobile and presents to a small rural hospital with a head and neck injury. His vital signs are stable. Glasgow Coma Scale=7. He is moving all extremities. There is a C3/4 fracture identified on xray. He is intubated at the rural hospital and transferred to you at the trauma centre.
Questions: Is CT angiography accurate for detecting blunt cerebrovascular injury?
Reference: Roberts et al. Diagnostic accuracy of computed tomography angiography for blunt cerebrovascular injury detection in trauma patients: A systematic review and meta-analysis, Ann Surg 2013
- Population: Systematic review of 8 studies enrolling patients >16 years after sustaining blunt trauma with suspected blunt cerebrovascular injury (BCVI) based on risk factors or clinical signs. N=1426 patients presenting to United States trauma centres.
- Intervention: CT angiography (CTA) of carotid and vertebral arteries
- Comparison: Digital subtraction angiography (DSA) of carotid and vertebral arteries
- Outcome: Summary diagnostic accuracy of CTA compared to DSA for blunt cerebrovascular injury.
Authors’ Conclusions: “Existing evidence suggests that the diagnostic performance of CTA varies considerably across studies, likely due to an implicit variation in diagnostic threshold across trauma centers. Moreover, although CTA appears to lack sensitivity to adequately rule out BCVI, it may be useful to rule in BCVI among trauma patients with a high pretest probability of injury.”
Quality Checklist for Systematic Review:
- The diagnostic question is clinically relevant with an established criterion standard. Yes Comment: Though invasive and labour intensive, digital subtraction angiography is currently the criterion standard for detection of cerebrovascular injury.
- The search for studies was detailed and exhaustive. Yes
- The methodological quality of primary studies were assessed for common forms of diagnostic research bias. Yes
- The assessments of studies were reproducible. Yes
- There was low heterogeneity for estimates of sensitivity or specificity. No
- The summary diagnostic accuracy is sufficiently precise to improve upon existing clinical decision making models. No
Key Results: Eight studies with a total 5704 carotid or vertebral arteries in 1426 trauma patients were included. Pool results for blunt cerebrovascular injury detection with CTA vs. digital subtraction angiography.
Sensitivity 66%, Specificity 97%, +LR 20 and -LR 0.35
- Primary Outcome:
- Sensitivity 66% (95% CI 49-79%) I2 =80 (lots of heterogeneity)
- Specificity was 97% (95% CI 91-99%) I2=94
- +LR was 20 (95% CI 6.9-58.4) I2=88
- -LR was 0.35 (95% CI 0.22-0.56) I2=75
This was a well-performed SR/MA. However, most of the studies included had unclear blinding. There was also a problem with heterogeneity was in all the measures between studies. Sources of heterogeneity might include who was reading the CTA, CT modality (16 or fewer slices), or diagnostic threshold variability between studies.
This study discussed likelihood ratios for diagnostic value of the test. If you have a LR of 1 it means no effect. However, if you have a +LR of >10 it is highly diagnositic for ruling in the condition. If you have a –LR of <0.1 it is highly diagnostic of ruling out the condition.
This review shows diagnostic accuracy of CTA for blunt cerebrovascular injury varies across institutions. While the pooled -LR was inadequate to rule-out blunt cerebrovascular injury at 0.35. This is greater than the <0.10 to feel confident about ruling out a condition.
On the other hand, the +LR of 20 warrants consideration in ruling in the injury for those with high pre-test probability. Further study with a standard diagnostic threshold is required.
If ultimately deemed to be specific enough, CTA will allow testing for an easily missed but devastating injury without resorting to a cumbersome and time- consuming procedure. However, this review will not be the last word on the matter.
Comment on Authors’ Conclusion Compared to Our Conclusion: We agree there is significant variability in the sensitivity of CTA for blunt cerebrovascular injury across institutions, a conclusion that, on its own, warrants further study to confirm why this is the case.
SGEM Bottom Line: Blunt cerebrovascular injury is an uncommon but dangerous injury to miss. Unfortunately, the current best test to confirm the problem remains one that is onerous to perform and not as widely available as CT.
Case Resolution: You have a high pre-test probability this man has a blunt cerebrovascular injury. You get a CT angiography which is negative. A digital subtraction angiography is performed and demonstrates a blunt cerebrovascular injury. He is sent to the appropriate referral service to address this rare but critical injury.
Clinical Application A negative CTA in a patient with high suspicion for blunt cerebrovascular injury warrants further work up with digital subtraction angiography.
What Do I Tell My Patient We are uncertain whether a CT scan of the blood vessels in your head and neck will confidently exclude significant injuries. For the time being, if you’ve suffered a serious head or neck injury, it’s better to be at a trauma centre with an interventional radiologist who can perform the more invasive and time-consuming test to exclude these injuries. However, if an interventional radiologist is unavailable and a CT angiogram demonstrates a significant injury, we will consult the surgeons immediately.
Keener Kontest: Winner last week was Dr. Ellie Wallace an Emergency Medicine resident at Boston Medical Center, in Boston, MA. She knew The sphygmomanometer was invented by Samuel Ritter von Basch in 1881.
Listen to the podcast to hear this weeks keener question. If you know the answer send an email to TheSGEM@gmail.com with “keener” in the subject line. The first person to correctly answer the question will receive a cool skeptical prize.