On a plain chest radiograph, which sign indicates a left-sided aortic arch with aberrant right subclavian artery (arteria lusoria)?

• A Right-sided aortic knuckle
• B Double aortic arch with bilateral vascular impressions on the trachea
• C Absent aortic knuckle on plain X-ray
• D Normal left aortic knuckle with an oblique soft-tissue band crossing the superior mediastinum from left to right at the level of T3–T4 ✓

Explanation

An aberrant right subclavian artery (the most common aortic arch anomaly, ~0.5% of population) arises as the last branch of a left aortic arch. On plain CXR, it may be visible as a soft-tissue band obliquely crossing the superior mediastinum from left-inferior to right-superior, at the level of T3–T4, posterior to the oesophagus. The aortic knuckle remains on the left. Double aortic arch causes bilateral tracheal indentations. Right-sided aortic knuckle indicates a right-sided aortic arch.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.