In an older adult with cardiovascular risk factors, what is the preferred imaging study to evaluate a pleural effusion and delineate a thoracic aortic aneurysm, considering possible contrast contraindications?

CT Imaging for Pleural Effusion and Thoracic Aortic Aneurysm

CT angiography (CTA) of the chest with intravenous contrast is the preferred single imaging study to simultaneously evaluate both pleural effusion and thoracic aortic aneurysm, providing comprehensive anatomic information with near 100% sensitivity and 98% specificity for aortic pathology while also characterizing pleural disease. 1, 2

Optimal Imaging Protocol

Primary Recommendation: CTA Chest with IV Contrast

For patients who can receive iodinated contrast, perform ECG-gated CTA chest with IV contrast as the definitive study. 1, 2 This single examination addresses both clinical concerns:

• Aortic aneurysm evaluation: CTA provides complete 3D dataset of the entire thoracic aorta, accurately measuring aneurysm size, detecting dissection, intramural hematoma, penetrating ulcers, thrombus, and atherosclerotic disease 1
• Pleural effusion characterization: Contrast-enhanced CT distinguishes between transudates and exudates, identifies pleural thickening, nodules, and loculations that indicate exudative effusions 3

Technical Specifications

ECG-gated acquisition is essential to eliminate cardiac motion artifacts in the ascending aorta and ensure reproducible measurements in the same cardiac phase 1, 2. Studies demonstrate 5-10% variation in proximal descending aortic measurements between systole and diastole 1.

Dual-phase protocol (non-contrast followed by contrast-enhanced) should be performed when intramural hematoma or aortic dissection are suspected 1. The non-contrast phase detects subtle IMH changes that may be masked on contrast images 1.

Multiplanar reconstructions and 3D rendering are mandatory components of CTA, not optional enhancements 1, 2. These allow accurate orthogonal measurements of the aorta and comprehensive surgical planning 1.

Management of Contrast Contraindications

If Contrast is Contraindicated

For patients with severe renal insufficiency or contrast allergy, MRA chest is the appropriate alternative for aortic evaluation, though it provides less information about pleural effusion 2, 4.

Non-contrast CT chest alone has limited utility but can detect:

• Changes in aortic diameter and identify intramural hematoma 1
• Presence and extent of pleural effusion 3
• Mediastinal or pericardial hemorrhage suggesting aortic rupture 1

However, non-contrast CT cannot adequately characterize the aortic aneurysm morphology, detect dissection flaps, or differentiate pleural effusion etiologies 1, 3.

Staged Approach for High-Risk Patients

If contrast risk is moderate, consider risk stratification: The radiation dose from thoracic CTA averages 10-15 mSv, and iodinated contrast carries risks of allergic reactions and contrast-induced nephropathy 1. However, the diagnostic accuracy of CTA (sensitivity 100%, specificity 98-99%) far exceeds alternative modalities for aortic disease 1, 5.

Field of View Considerations

Extend imaging from thoracic inlet through the pelvis if surgical or endovascular repair is being considered 1. This provides critical information about:

• Iliofemoral artery diameters, calcification, and tortuosity for TEVAR planning 1
• Branch vessel involvement 1
• Complete extent of aortic pathology 1

For isolated thoracic pathology on prior imaging, chest-only CTA is acceptable for follow-up studies 1.

Critical Pitfalls to Avoid

Non-ECG-gated CT creates motion artifacts in the ascending aorta that can simulate aortic dissection—the "double contour" or pseudodissection appearance 1, 5. This is a common diagnostic trap that leads to unnecessary intervention.

Standard "CT chest with contrast" ordered from routine protocols typically lacks:

• ECG gating 1
• Thin-section acquisition 1
• Arterial-phase bolus timing 1
• 3D rendering 1

Explicitly order "CTA chest" to ensure proper protocol, not simply "CT chest with contrast" 1, 2.

Measurements must be orthogonal to the aortic longitudinal axis, not in the axial plane, using multiplanar reformatted images with centerline correction 1, 2. Axial measurements systematically overestimate aneurysm size in tortuous aortas.

Alternative Modalities: Limited Roles

Transesophageal echocardiography has a critical "blind spot" in the distal ascending aorta due to tracheal and bronchial interposition, making it unreliable for complete thoracic aortic evaluation 1, 2, 5. TEE requires sedation, blood pressure control, and esophageal disease exclusion 1.

Chest radiography cannot adequately evaluate either condition and should only serve as an initial screening tool 5.