Recommended Imaging for Suspected Aortic Dissection
CT angiography (CTA) of the chest is the first-line imaging modality for suspected aortic dissection in the emergency setting. 1
Why CTA is the Preferred Initial Test
CTA has emerged as the standard of reference for diagnosing aortic dissection due to several critical advantages:
- Diagnostic accuracy is exceptional, with pooled sensitivity of 100% and specificity of 98% for detecting aortic dissection 1
- Speed and availability are unmatched, with 24/7 accessibility in emergency departments and rapid image acquisition that allows for quick diagnosis and treatment 1
- Comprehensive anatomic detail shows the full extent of dissection, entry tear sites, branch vessel involvement, and complications including malperfusion syndromes, pericardial effusion, hemopericardium, periaortic or mediastinal hematoma, and pleural effusion 1
- Sensitivity and specificity exceed 99% in multiple studies, making it highly reliable for ruling in or ruling out dissection 2
Optimal CTA Protocol
Order ECG-gated CTA with both non-contrast and contrast-enhanced phases:
- ECG-gated acquisition reduces motion artifacts of the aortic root and thoracic aorta, improving diagnostic accuracy 1
- Non-enhanced CT followed by contrast-enhanced angiography is the recommended protocol, particularly important for detecting intramural hematoma which may be missed on contrast-only studies 1
- Scan the entire aorta from the aortic sinus through the iliac bifurcation, as patients with thoracic aortic pathology have increased incidence of abdominal aortic disease 3
However, a chest-only protocol can be considered initially to reduce radiation exposure, with abdominopelvic imaging added only if clinically indicated, as this approach reduces radiation dose by 14.6% without compromising diagnostic accuracy 4
When to Use Alternative Imaging
Transesophageal echocardiography (TEE) should be ordered when:
- The patient has a contraindication to iodinated contrast (severe contrast allergy or renal failure) 1
- The patient is too hemodynamically unstable to transport to the CT scanner 1
- Rapid bedside assessment is needed in a critically ill patient 1
MRI/MRA should be considered when:
- The patient is stable but has a contraindication to iodinated contrast 1
- Follow-up imaging is needed to reduce cumulative radiation exposure 1
Critical Pitfalls to Avoid
Do not rely on chest X-ray alone to rule out dissection—while abnormal in 60-90% of cases, it lacks the sensitivity and specificity needed for definitive diagnosis 5
Be aware of CT artifacts that can mimic dissection, including:
- Motion artifacts in the ascending aorta that can create false positives 1
- Streak artifacts from implanted devices 3
- Periaortic structures such as aortic arch branches, mediastinal veins, and pericardial recesses that may simulate dissection 6
Do not delay imaging in patients with moderate to high clinical suspicion—mortality increases by 1-2% per hour in untreated aortic dissection 5, 7
Consider ordering a second imaging test if the first is negative and clinical suspicion remains high (probability >15-35% depending on initial test used), as the benefits of a second test outweigh the risks when obtained within 10 hours 7