What is the recommended imaging modality for aneurysmal dilation of the ascending thoracic aorta?

Imaging for Aneurysmal Dilation of the Ascending Thoracic Aorta

For ascending thoracic aortic aneurysms, transthoracic echocardiography (TTE) is recommended at initial diagnosis to assess the aortic root and proximal ascending aorta, but cardiovascular computed tomography (CCT) or cardiovascular magnetic resonance (CMR) must be used to confirm measurements, rule out asymmetry, and establish baseline diameters for surveillance. 1

Initial Diagnostic Approach

Transthoracic Echocardiography (TTE)

• TTE is the recommended first-line imaging modality for screening the aortic root and proximal ascending aorta at diagnosis 1
• TTE effectively visualizes the aortic root and proximal ascending aorta, and provides critical assessment of aortic valve anatomy and function 1
• Major limitation: The mid-ascending aorta requires dedicated views, and the distal ascending aorta is often incompletely visualized 1
• TTE measurements may be limited in obese patients, intubated patients, or those with chest wall alterations, pneumothorax, or emphysema 1

Cross-Sectional Imaging Confirmation

CCT or CMR is mandatory to confirm TTE measurements, rule out aortic asymmetry, and determine baseline diameters for follow-up 1. This is a Class I recommendation from the 2024 ESC Guidelines.

Computed Tomography Angiography (CTA)

CTA is the primary modality for comprehensive assessment of the entire thoracic aorta 1:

• Provides complete 3D visualization of the entire aorta and proximal branch vessels with electrocardiogram-gated acquisition 1
• Allows accurate, reproducible measurements using the double oblique method with multiplanar reconstructions 1
• Short scan time, wide availability, and low operator dependence 1
• Essential before planned operative intervention for comprehensive assessment of the entire aorta and branch vessels 1
• Can simultaneously assess coronary arteries, potentially avoiding invasive coronary angiography 1

Disadvantages: Radiation exposure and risk of contrast nephropathy 1

Cardiovascular Magnetic Resonance (CMR)

CMR is preferred for young patients requiring repetitive studies and long-term surveillance 1:

• No ionizing radiation, making it ideal for serial imaging in younger patients 1
• Superior anatomic assessment of the entire aorta comparable to CT 1
• Can effectively characterize inflammatory medial changes 1
• Provides functional and biomechanical information beyond simple diameter measurements 2

Surveillance Imaging Strategy

For Aortic Root and Proximal Ascending Aorta

• If TTE and CCT/CMR measurements agree (within 3 mm), TTE can be used for follow-up 1
• If measurements differ by ≥3 mm, surveillance must be performed by CMR or CCT 1

For Distal Ascending Aorta, Arch, or Descending Thoracic Aorta

• TTE is NOT recommended for surveillance of these locations 1
• CMR or CCT is required for surveillance of aneurysms at the distal ascending aorta, aortic arch, or descending thoracic aorta 1

Surveillance Intervals

Initial imaging at 6-12 months after diagnosis to ensure stability, then:

• Annually if no expansion/extension, customized according to baseline diameter and underlying condition 1
• Every 6 months if rapid expansion (≥3 mm per year) or approaching surgical threshold (50-55 mm range) 1
• Intervals may be lengthened if stability demonstrated over years, especially in non-genetic aneurysms <45 mm 1

Critical Measurement Technique

The double oblique method is the standardized approach for measuring ascending aortic diameter 1:

• Creates reformatted views perpendicular to blood flow 1
• Corrects for the oblique course and tortuosity of the ascending aorta 1
• Non-standard measurement approaches lead to unreliable reporting and management conflicts 1

Common Pitfalls to Avoid

• Do not rely solely on TTE for distal ascending aorta, arch, or descending aorta - these locations have a "blind spot" for echocardiography 1
• Do not use transverse diameter measurements - these are less accurate than the double oblique perpendicular method 1
• Do not perform surveillance with different imaging modalities - use the same technique and ideally the same center for consistency 1
• Do not forget to assess the entire aorta when an aneurysm is identified at any location 1