From the Guidelines
Cardiac-gated CT or MRI is the recommended imaging modality for diagnosing an ascending aortic aneurysm, with the choice between them depending on patient characteristics, institutional expertise, renal function, affordability, and radiation exposure concerns. When considering the best approach for imaging an ascending aortic aneurysm, it's crucial to prioritize modalities that offer superior visualization of the aortic root and ascending aorta. According to the 2022 ACC/AHA guideline for the diagnosis and management of aortic disease 1, cardiac-gated CT or MRI provides the best images of these areas, especially when transthoracic echocardiography (TTE) is inadequate.
The advantages of CT include its wide availability, speed, and ability to provide detailed information about the aneurysm's relationship to adjacent structures and branch vessels. However, for patients with contraindications to CT, such as renal insufficiency or contrast allergy, MRI is an excellent alternative that avoids radiation and iodinated contrast 1. MRI's role is particularly valued in stable patients with contraindications to iodinated contrast, where it can serve as the preferred modality for diagnosis.
Key considerations in choosing between CT and MRI include:
- Patient characteristics, such as renal function and history of contrast reactions
- Institutional expertise and availability of the imaging modalities
- Affordability and concerns about radiation exposure
- The specific clinical questions to be answered by the imaging study
While transthoracic echocardiography (TTE) may be used as an initial screening tool, it has limitations in fully visualizing the ascending aorta. Transesophageal echocardiography (TEE) provides better visualization but is more invasive. The choice of initial imaging modality should be based on the patient's history, clinical presentation, and the specific clinical questions to be answered, as well as institutional availability and expertise 1.
Regular follow-up imaging is essential once an ascending aortic aneurysm is diagnosed, typically using the same modality as the initial diagnosis to ensure consistent measurements. The frequency of follow-up imaging depends on factors such as aneurysm size, growth rate, and underlying etiology, but generally occurs every 6-12 months for aneurysms approaching surgical thresholds.
From the Research
Imaging Modalities for Diagnosing Ascending Aortic Aneurysm
The diagnosis of an ascending aortic aneurysm can be achieved through various imaging modalities, each with its strengths and limitations. The choice of imaging modality depends on several factors, including the location of the aneurysm, the reason for the study, and patient characteristics.
- Ultrasound: Ultrasound, including transthoracic echocardiography (TTE), is highly useful in the diagnosis and follow-up of proximal ascending aorta aneurysms 2, 3. However, it may have limitations in assessing the entire aorta and adjacent structures.
- Computed Tomography (CT): CT plays a central role in the diagnosis, risk stratification, and management of most aneurysms, particularly those located distal to the proximal ascending aorta 2, 4, 5. CT offers rapid image acquisition, multiplanar capacity, and high spatial resolution, but it involves radiation exposure and the need for nephotoxic contrast administration.
- Magnetic Resonance Imaging (MRI): MRI is less readily available but overcomes the limitations of CT, including radiation exposure and the need for contrast administration 2, 4. MRI is mainly indicated in young individuals who require repetitive studies and long-term follow-up.
- Transesophageal Echocardiography (TEE): TEE is frequently limited to perioperative indications but can provide valuable information on the ascending aorta and adjacent structures 2, 3.
Comparison of Imaging Modalities
Studies have compared the accuracy of different imaging modalities in measuring ascending aortic aneurysms. For example, a study found that inner-to-inner "cusp to cusp" diameter measured on an ECG-gated CT should be used for comparison with 2D TTE aortic diameter at the level of the sinuses of Valsalva in patients with thoracic aortic aneurysms 6.
Multimodality Imaging
Multimodality imaging, including CT, MRI, and echocardiography, has advanced the field of aortic imaging and is critical in identifying acute aortic syndromes and other associated complications of aortic aneurysms, as well as in long-term follow-up 4, 3.