From the Guidelines
The best imaging modality for suspected aortic dissection is CT angiography (CTA) with intravenous contrast. This recommendation is based on the most recent and highest quality study, which emphasizes the importance of rapid and accurate diagnosis in suspected aortic dissection cases 1.
Key Points to Consider
- CTA should be performed immediately when aortic dissection is suspected, as it offers rapid acquisition, high sensitivity (95-100%), and specificity (95-98%), as well as widespread availability in emergency settings.
- The scan should include the entire aorta from arch to iliac bifurcation to evaluate the full extent of dissection.
- CTA provides excellent visualization of the intimal flap, false lumen, branch vessel involvement, and complications such as rupture or malperfusion.
- Alternative options include transesophageal echocardiography (TEE) for unstable patients who cannot be transported, or MRI for patients with contrast allergies or renal dysfunction, though MRI takes longer and may not be feasible in emergent situations.
- Conventional chest X-rays may show mediastinal widening but lack sensitivity and should not delay definitive imaging.
Clinical Considerations
- Time is critical in aortic dissection management, as mortality increases approximately 1-2% per hour without treatment, so obtaining appropriate imaging rapidly is essential for timely surgical or medical intervention.
- The choice of imaging modality should be based on the patient's history, clinical presentation, and institutional availability, as well as the specific clinical questions to be answered 1.
- Electrocardiogram (ECG)-gated acquisition protocols are crucial in reducing motion artifacts of the aortic root and thoracic aorta, and high-end MSCT scanners are preferred for their higher spatial and temporal resolution 1.
From the Research
Imaging Modalities for Suspected Aortic Dissection
The best imaging modality for suspected aortic dissection can depend on various factors, including the patient's condition, availability of equipment, and potential contraindications. The following are some of the commonly used imaging modalities:
- Computed Tomography (CT) Angiography: CT angiography is a highly sensitive and specific imaging modality for detecting aortic dissection 2, 3, 4. It can provide detailed images of the aorta and its branches, and is particularly useful for evaluating the extent of the dissection and identifying any complications.
- Magnetic Resonance (MR) Angiography: MR angiography is another highly sensitive and specific imaging modality for detecting aortic dissection 2, 5, 3. It is particularly useful for patients with contraindications to CT angiography, such as renal insufficiency or iodinated contrast allergy.
- Transesophageal Echocardiography (TEE): TEE is a sensitive and specific imaging modality for detecting aortic dissection, particularly in the ascending aorta 2, 3. It is also useful for evaluating the aortic valve and detecting any complications such as aortic regurgitation.
- Helical Computed Tomography: Helical computed tomography is a type of CT scan that uses a spiral motion to image the aorta and its branches 3. It is highly sensitive and specific for detecting aortic dissection, and can provide detailed images of the aorta and its branches.
Advantages and Disadvantages of Each Modality
Each imaging modality has its advantages and disadvantages, including:
- CT Angiography:
- Advantages: highly sensitive and specific, rapid imaging time, widely available
- Disadvantages: uses ionizing radiation, may require contrast agents
- MR Angiography:
- Advantages: highly sensitive and specific, no ionizing radiation, can be used in patients with contraindications to CT angiography
- Disadvantages: may require longer imaging time, may not be available in all institutions
- TEE:
- Advantages: highly sensitive and specific, can be used in patients with contraindications to CT angiography, provides real-time imaging
- Disadvantages: may be uncomfortable for patients, requires specialized equipment and training
- Helical Computed Tomography:
- Advantages: highly sensitive and specific, rapid imaging time, widely available
- Disadvantages: uses ionizing radiation, may require contrast agents
Clinical Decision Support and Radiation Exposure
The use of clinical decision support systems can help reduce radiation exposure in patients suspected of having aortic dissection 4. By implementing a dedicated CT protocol that forgoes routine abdominopelvic imaging, radiation dose can be significantly reduced without compromising diagnostic accuracy. Additionally, the use of reformatted images can be crucial in evaluating patients with fibromuscular dysplasia, a condition that may increase the risk of aortic dissection 6.