What type of scan is recommended for diagnosing an ascending and descending aortic aneurysm?

Diagnostic Imaging for Ascending and Descending Aortic Aneurysms

For suspected ascending and descending aortic aneurysms, computed tomography angiography (CTA) is the recommended initial diagnostic imaging modality due to its high sensitivity (up to 100%) and specificity (98-99%) for detecting thoracic aortic disease. 1

Initial Diagnostic Approach

• Chest X-ray is inadequately sensitive to definitively exclude thoracic aortic aneurysms, with sensitivity of only 64% for widened mediastinum and 71% for abnormal aortic contour 1, 2
• CT is preferred over echocardiography for identifying thoracic aortic disease and other conditions that can mimic aortic disease (pulmonary embolism, pericardial disease) 1
• CTA uses thin-section CT acquisition timed to coincide with peak arterial enhancement, with multiplanar reformations and 3D renderings, allowing complete visualization of the entire aorta 1

Specific Imaging Recommendations by Modality

Computed Tomography (CT/CTA)

• CTA provides comprehensive evaluation of the entire aorta, including lumen, wall, and periaortic regions 1
• CTA can identify anatomic variants, branch vessel involvement, and distinguish between different types of acute aortic syndromes 1
• ECG-gated techniques allow motion-free images of the aortic root and coronary arteries 1
• External aortic diameter should be reported for CT measurements, as lumen size may not accurately reflect external diameter in cases with intraluminal clot or wall inflammation 1

Magnetic Resonance Imaging (MRI/MRA)

• MRI may be preferred for patients requiring repeated imaging to follow aortic abnormalities, particularly in younger patients to minimize radiation exposure 1, 2
• MRI has comparable diagnostic accuracy to CT for thoracic aortic disease 2
• MRI may require sedation due to longer examination times and tendency for claustrophobia 1

Echocardiography

• Transthoracic echocardiography (TTE) is useful for evaluating the aortic root and ascending aorta but has limitations for the aortic arch 1
• Transesophageal echocardiography (TEE) provides high-resolution images of the thoracic aorta but is semi-invasive and requires sedation 1
• Echocardiography reports internal diameter measurements, in contrast to CT/MRI which report external diameter 1

Follow-up Imaging Recommendations

• For patients with borderline abnormal renal function (serum creatinine >1.8-2.0 mg/dL), consider the tradeoffs between iodinated contrast for CT (risk of contrast-induced nephropathy) and gadolinium for MRI (risk of nephrogenic systemic fibrosis) 1
• After intervention or open surgery, CT is preferred to detect asymptomatic post-procedural leaks or pseudoaneurysms 1
• Follow-up imaging frequency depends on aneurysm size and growth rate:
  • Ascending aortic aneurysms grow at an average rate of 0.07 cm per year 3
  • Descending aortic aneurysms grow at an average rate of 0.19 cm per year 3
  • Growth rates ≥3 mm/year for thoracic aorta or ≥10 mm/year for abdominal aorta are considered high-risk features 1

Measurement Standards and Critical Thresholds

• Aneurysm is defined as approximately 5.0 cm for the ascending aorta and 4.0 cm for the descending aorta (150% of normal diameter) 1
• Diameters between normal and aneurysm are considered dilated or ectatic 1
• Critical sizes associated with complications (rupture or dissection) are 6.0 cm for the ascending aorta and 7.0 cm for the descending aorta 3
• Standardization of aortic diameter measurements is important for planning potential endovascular treatment 1

Important Considerations

• Radiation exposure should be minimized, especially in neonates, children, and young adults 1
• A centerline of flow measurement technique reduces the error of tangential measurement and allows true short-axis measurement of aortic diameter 1
• Thoracic aortic aneurysms are often asymptomatic and diagnosed incidentally during unrelated imaging or screenings 1
• When evaluating CT or MRI results, measurements should be taken at the same level of the aorta for accurate assessment of progression rates 1

By following these imaging recommendations, clinicians can accurately diagnose and monitor ascending and descending aortic aneurysms, allowing for timely intervention when necessary.