Flat waist sign

Last revised by Craig Hacking on 13 Feb 2019

The flat waist sign refers to flattening of the left heart border, specifically the contours of the aortic arch and adjacent pulmonary trunk. It is seen in severe left lower lobe collapse and is caused by leftward displacement and rotation of the heart.

It is different to the straight left heart border sign on CXR seen in hemopericardium secondary to penetrating chest trauma.

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Cases and figures

  • Case 1: partial flattening of the left heart border due to LLL collapse
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