From the Guidelines
Computed tomography (CT) is the preferred initial imaging modality for suspected aortic dissection due to its high sensitivity and specificity, rapid acquisition time, and widespread availability, as recommended by the 2022 ACC/AHA guideline for the diagnosis and management of aortic disease 1.
Key Considerations for Imaging
- The choice of imaging modality should be based on the patient's history and clinical presentation, as well as institutional availability and expertise 1.
- CT is widely available and can quickly diagnose the underlying aortic dissection, show the full extent of the dissection, and detect complications like malperfusion or rupture 1.
- Magnetic resonance angiography (MRA) is an excellent alternative for patients with contrast allergies or renal dysfunction, but it takes longer and may not be suitable for unstable patients 1.
- Transesophageal echocardiography (TEE) is valuable in unstable patients or when CT is unavailable, offering bedside assessment of the ascending aorta, arch, and proximal descending aorta with high sensitivity 1.
Imaging Protocol
- The CT scan should include the entire aorta from arch to iliac bifurcation with intravenous contrast to visualize the true and false lumens, entry tears, branch vessel involvement, and complications like malperfusion or rupture 2.
- Non-enhanced CT, followed by CT contrast-enhanced angiography, is the recommended protocol, particularly when intramural hematoma (IMH) or aortic dissection (AD) are suspected 3.
- Electrocardiogram (ECG)-gated acquisition protocols are crucial in reducing motion artefacts of the aortic root and thoracic aorta 3.
Follow-up Imaging
- Follow-up imaging is essential after initial diagnosis, typically with CT or MRA at 1, 3, 6, and 12 months, then annually thereafter, adjusting frequency based on stability and growth rate 1.
- Imaging selection should consider the patient's hemodynamic stability, with unstable patients requiring the fastest available modality, typically CT or bedside TEE 1.
From the Research
Imaging Modalities for Aortic Dissection
- Computed Tomography (CT) is a primary imaging modality for the diagnosis of aortic diseases, including aortic dissection, due to its minimal invasiveness and agility 4.
- Other imaging modalities used for diagnosing aortic dissection include transesophageal echocardiography (TEE), helical CT, and magnetic resonance imaging (MRI) 5, 6.
- These imaging techniques have comparable sensitivity and specificity, with pooled sensitivity ranging from 98-100% and specificity ranging from 95-98% 5.
- The choice of imaging modality may depend on the patient's risk profile and the presence of complications, such as aortic regurgitation 7.
Comparison of Imaging Modalities
- Spiral CT, multiplanar TEE, and MR imaging have been compared in the diagnosis of thoracic aortic dissection, with spiral CT showing superior sensitivity and specificity in detecting aortic arch vessel involvement 6.
- Intravascular ultrasound (IVUS) imaging has also been evaluated in the assessment of aortic dissection, demonstrating high accuracy in detecting intimal flaps and tears, as well as evaluating the size of the vessel and the extent of dissection 8.
- IVUS has been shown to be particularly useful in evaluating the abdominal aorta and determining the relation of branches to the false lumen 8.
Clinical Applications
- CT angiography (CTA) is considered the gold standard test for diagnosing aortic dissection, but may not always be foolproof, highlighting the importance of clinical suspicion and further imaging with TTE/TEE in certain cases 7.
- The use of multiple imaging modalities can provide complementary information and improve diagnostic accuracy in patients with suspected aortic dissection 5, 6, 7, 8.