When to Obtain CTA of the Aorta for Dilated Ascending Aorta
CTA of the aorta should be obtained when echocardiography cannot adequately visualize the ascending aorta beyond 4.0 cm from the valve plane, when confirming baseline measurements for surgical planning, or when assessing the entire aortic length in patients with genetic conditions or bicuspid aortic valve. 1
Primary Indications for CTA
Inadequate Echocardiographic Visualization
CTA (or cardiac MRI) is indicated when transthoracic echocardiography cannot accurately assess the morphology of the aortic sinuses, sinotubular junction, or ascending aorta. 1 This commonly occurs when the mid-ascending aorta is obscured by intervening lung tissue, limiting visualization beyond the proximal segments. 1
In patients with bicuspid aortic valve and dilated ascending aorta, if only the aortic sinuses can be visualized on TTE and the ascending aorta cannot be assessed to a distance ≥4.0 cm from the valve plane, additional imaging with CTA or MRI is required. 1
Confirmation and Baseline Establishment
After initial TTE diagnosis of ascending aortic dilation, CTA or MRI is reasonable to confirm the aortic diameters, rule out aortic asymmetry, and establish baseline measurements for future surveillance. 1 This is particularly important because CTA measurements are typically 1-2 mm larger than echocardiographic measurements due to inclusion of the aortic wall and differences in cardiac cycle timing. 1
CTA provides external diameter measurements perpendicular to the long axis of the aorta with higher spatial resolution than echocardiography, allowing for accurate surgical planning when diameters approach intervention thresholds. 1
Complete Aortic Assessment
- When any aortic aneurysm is identified at any location, assessment of the entire aorta is recommended at baseline and during follow-up. 1 CTA or MRI can display 3D reconstruction of the entire aortic length, which echocardiography cannot provide. 1
Specific Clinical Scenarios Requiring CTA
Bicuspid Aortic Valve
- Patients with bicuspid aortic valve require serial evaluation with echocardiography, CMR, or CTA when the aortic diameter exceeds 4.0 cm, with annual imaging recommended when diameter exceeds 4.5 cm. 1 CTA should be obtained if echocardiography is inadequate or when approaching surgical thresholds (≥5.0-5.5 cm). 1, 2
Genetic Conditions
In Marfan syndrome, while TTE is the primary surveillance modality, CTA or MRI is reasonable after initial TTE to confirm diameters and assess the remainder of the thoracic aorta. 1 This is particularly important because descending aortic and abdominal aortic aneurysms can occur, though less commonly than root involvement. 1
Patients with Loeys-Dietz syndrome require complete aortic imaging from cerebrovascular circulation to pelvis at initial diagnosis and 6 months thereafter, necessitating MRI (preferred) or CTA. 1
Surveillance of Distal Segments
- CTA or MRI is recommended for surveillance of aneurysms at the distal ascending aorta, aortic arch, descending thoracic aorta, or thoracoabdominal aorta, as TTE is not recommended for these locations. 1
Imaging Modality Selection: CTA vs MRI
When to Prefer MRI Over CTA
- MRI is preferred over CTA when possible in patients who will require multiple imaging studies over their lifetime due to absence of ionizing radiation exposure. 1 This is particularly relevant for young patients with bicuspid aortic valve or genetic conditions requiring lifelong surveillance.
When CTA is Appropriate
CTA is appropriate when MRI is contraindicated (pacemakers, claustrophobia, renal dysfunction precluding gadolinium), when rapid imaging is needed, or when surgical planning requires detailed anatomic assessment. 1
ECG-gated CTA is superior to non-gated CTA for ascending aortic assessment, reducing pulsation artifacts and improving diagnostic accuracy. 1, 3
Common Pitfalls to Avoid
Measurement Discrepancies
Never directly compare measurements from different imaging modalities without accounting for systematic differences. CTA/MRI measurements are typically 1-2 mm larger than echocardiographic measurements because they include the aortic wall and may represent average rather than end-diastolic values. 1
When establishing baseline measurements or assessing growth rates, use the same imaging modality and measurement technique for serial studies to ensure accuracy. 1
Delayed Advanced Imaging
- Do not delay obtaining CTA or MRI when echocardiographic visualization is suboptimal, particularly when diameters approach 4.5-5.0 cm where surgical decision-making becomes critical. 1, 2 Inadequate surveillance due to poor imaging quality can result in missed opportunities for prophylactic intervention.
Overlooking Distal Aortic Segments
- In patients with ascending aortic dilation, particularly those with bicuspid aortic valve or genetic conditions, failure to assess the entire aorta can miss concomitant arch, descending, or abdominal aortic pathology. 1 Complete aortic imaging with CTA or MRI should be performed at baseline when any thoracic aortic aneurysm is identified. 1