What are the next steps if a chest X-ray shows an atypical left cardiomediastinal contour suggesting an aortic (Aorta) aneurysm or a left hilar mass, and how can I determine if it's an artifact or a pathological finding?

Atypical Left Cardiomediastinal Contour: Diagnostic Approach

Proceed immediately to definitive cross-sectional imaging with CT angiography, as chest X-ray findings of abnormal aortic contour or left hilar mass have only 64-71% sensitivity for detecting significant thoracic aortic disease and cannot reliably distinguish artifact from true pathology. 1

Why Chest X-Ray Alone is Insufficient

• Chest X-ray has a specificity of only 86% for aortic pathology, meaning false positives are common and further imaging is mandatory to avoid missing life-threatening conditions 1
• The sensitivity for detecting aortic disease is particularly poor (47%) when pathology is confined to the proximal/ascending aorta, even when abnormalities are visible on chest film 2
• Mediastinal contour abnormalities are more often false positive than true positive, especially in trauma cases where venous bleeding can mimic aortic injury 1
• A completely normal chest X-ray lowers the likelihood of aortic disease only in very low-risk patients, but abnormal findings mandate definitive imaging regardless of clinical risk 1, 3

Immediate Next Step: CT Angiography

Order contrast-enhanced CT angiography of the chest as the first-line definitive imaging study. 1, 3

Why CT is Preferred:

• Near-universal availability with sensitivity up to 100% and specificity of 98-99% for thoracic aortic disease 1, 3
• Images the entire aorta including lumen, wall, and periaortic regions in a single rapid study 1
• Distinguishes between aortic aneurysm, dissection, intramural hematoma, and penetrating ulcer 1
• Identifies alternative diagnoses that can mimic aortic disease (pulmonary embolism, hiatal hernia, mediastinal masses) 4
• Can definitively differentiate a true left hilar mass from vascular pathology with contrast enhancement 5, 6

CT Protocol Specifics:

• Use ECG-gated technique if available for motion-free images of the aortic root 1
• Include both pre-contrast and post-contrast phases to detect intramural hematoma 1
• Ensure coverage from thoracic inlet to diaphragm to capture entire thoracic aorta 1

Alternative Imaging in Specific Scenarios

For hemodynamically unstable patients: Use transesophageal echocardiography (TEE) at bedside, which provides immediate assessment of aortic pathology and valve function while allowing continuous monitoring 3

If CT is contraindicated (renal failure, contrast allergy): MRI provides comparable diagnostic accuracy and is preferred for serial follow-up imaging 3

Critical Clinical Context to Assess

Before ordering imaging, rapidly evaluate these high-risk features that increase pretest probability of true aortic pathology (not artifact): 1

• Pain characteristics: Abrupt onset, severe intensity, ripping/tearing quality
• High-risk conditions: Marfan syndrome, Loeys-Dietz syndrome, vascular Ehlers-Danlos, Turner syndrome, known aortic aneurysm, recent aortic manipulation
• Physical examination: Pulse deficit, blood pressure differential >20 mmHg between limbs, new aortic regurgitation murmur, focal neurologic deficits
• Family history: Aortic dissection or thoracic aneurysm in first-degree relatives

What CT May Reveal

The differential diagnosis for atypical left cardiomediastinal contour includes: 5, 6

• Aortic aneurysm: Look for fusiform or saccular dilatation, mural calcification ("porcelain aorta"), mural thrombus 1
• Aortic pseudoaneurysm: Narrow "neck" leading to contained rupture, often post-traumatic 1, 5
• Anatomic variants: Right-sided aortic arch with aberrant vessels, aortic unfolding/tortuosity in elderly 7
• True hilar mass: Lung cancer, lymphoma, lymphadenopathy - distinguished by lack of vascular enhancement and presence of mediastinal adenopathy 5
• Artifact: Isolated aortic bands or contour irregularities without mediastinal hematoma, especially when other findings are absent 6

If Initial CT is Negative but Suspicion Remains High

Obtain a second imaging study using a different modality (TEE or MRI) if clinical features strongly suggest aortic disease despite negative CT. 3 This is particularly important in patients with high-risk pain features or examination findings, as no single imaging test has 100% sensitivity.

Common Pitfalls to Avoid

• Never rely on chest X-ray alone to exclude aortic pathology - even a "normal" mediastinal contour does not rule out dissection or aneurysm 1, 3, 2
• Do not assume abnormal contour is artifact without definitive imaging - the consequences of missing aortic dissection or rupture are catastrophic 1, 2
• Beware of isolated mediastinal hematoma on CT without direct aortic injury signs - this often represents venous bleeding rather than arterial injury and may not require aortography 6
• Consider anatomic variants in asymptomatic patients - right-sided aortic arch or aberrant vessels can create unusual contours but still warrant full aortic imaging to document anatomy 7