Aortic knob

Last revised by Dr Henry Knipe on 27 Jun 2018

The aortic knob or knuckle refers to the frontal chest x-ray appearance of the distal aortic arch as it curves posterolaterally to continue as the descending thoracic aorta. It appears as a laterally-projecting bulge, as the medial aspect of the aorta cannot be seen separate from the mediastinum. It forms the superior border of the left cardiomediastinal contour.

Related pathology

The aortic knob may become enlarged in:

The aortic knob may be small or absent in:

The aortic knob may be obscured by:

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Cases and figures

  • Figure 1
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  • Case 1: thoracic aortic aneurysm
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