Imaging for Ascending Aortic Aneurysm
CT angiography (CTA) of the chest is the primary imaging modality for comprehensive assessment of an ascending aortic aneurysm. 1
Why CTA is the Gold Standard
CTA with intravenous iodinated contrast is the primary modality used in the comprehensive assessment of the thoracic aorta, providing complete visualization of the entire aorta and proximal branch vessels with electrocardiogram-gated acquisition. 1 The American College of Radiology explicitly recommends CTA as the next imaging modality for suspected aortic arch and ascending aortic aneurysms, offering high sensitivity and specificity with detailed assessment of aneurysm location, size, and relationship to branch vessels. 2
Key Advantages of CTA
Comprehensive anatomic coverage: CTA visualizes the entire aorta from aortic sinus through the iliac bifurcation, which is critical since patients with thoracic aortic pathology have increased incidence of abdominal aortic disease. 1, 3
Superior technical capabilities: CTA provides short scan time, ability to obtain 3-dimensional datasets, wide availability, and low operator dependence compared to other modalities. 1
Detection of complications: CTA readily identifies acute disease states including aortic dissection, intramural hematoma, penetrating ulcer, and thrombus. 1
Preoperative planning: CTA allows assessment of the coronary arterial system, potentially avoiding the need for invasive coronary angiography before surgical intervention. 1
Critical Technical Requirements
ECG-gated CTA acquisition is essential to minimize cardiac motion artifact and allow for accurate orthogonal measurement of the thoracic aorta. 2 The scan must include three required elements: (1) timing to coincide with peak arterial enhancement, (2) multiplanar reformations, and (3) 3D renderings. 1
Accurate measurement requires the double oblique method using multiplanar reconstructions to create a reformatted view perpendicular to blood flow, correcting for the oblique course and tortuosity of the ascending aorta. 1 This standardized approach is recommended in guideline statements, as nonstandard measurement techniques may lead to unreliable reporting with consequent conflicts in management. 1
When Non-Contrast CT is Acceptable
Non-enhanced CT with multiplanar reconstructions is adequate for initial diagnosis of suspected thoracic aortic aneurysm and for delineating abnormal aortic findings such as atherosclerotic plaque, though it is limited in evaluating acute complications. 1 Non-contrast CT can still provide valuable information about aortic size and wall calcifications in patients who cannot tolerate iodinated contrast, albeit with reduced diagnostic accuracy. 2
Alternative Imaging Modalities
MR Angiography (MRA)
MRA is an acceptable alternative when CTA is contraindicated, providing similar sensitivity and specificity while avoiding ionizing radiation and iodinated contrast. 2 MRA is commonly used for surveillance of thoracic aortic aneurysms, especially in young patients requiring routine follow-up. 1 However, MRA has limitations including longer acquisition times, limited ability to characterize aortic wall calcifications, and reduced availability. 1
Transthoracic Echocardiography (TTE)
TTE is frequently the initial screening test for the aortic root and proximal ascending aorta, but does not provide comprehensive assessment of the entire aorta. 1 The aortic root and proximal ascending aorta are generally easily visualized, whereas the mid-ascending aorta requires dedicated views, and the distal ascending, arch, and descending thoracic aorta are generally incompletely visualized in adult patients. 1
Transesophageal Echocardiography (TEE)
TEE can be considered in unstable patients who cannot be transported for CTA or when rapid bedside assessment is needed, useful for evaluating the aortic root and associated valvular abnormalities. 2 However, TEE has a significant "blind spot" in the anterior aortic arch due to the trachea and left main bronchus blocking sound waves between the esophagus and aorta. 1
Critical Pitfalls to Avoid
Do not rely solely on chest radiography: While findings such as widened mediastinum or aortic tortuosity may suggest aneurysm, CXR is neither sensitive nor specific enough for definitive diagnosis and requires confirmatory cross-sectional imaging. 1, 2
Avoid non-ECG-gated studies when possible: Non-gated acquisitions may have variable image quality through the aortic root and coronary vessels due to cardiac motion artifact. 2
Be aware of device-related artifacts: Streak artifacts from implanted devices can limit CTA evaluation and potentially mimic pathology. 2, 3
Ensure proper measurement technique: Using non-standardized measurement approaches rather than the double oblique method perpendicular to blood flow can lead to inaccurate sizing and inappropriate management decisions. 1