Double density sign | Radiology Signs

Answer:

Enlargement of the left atrium creates a second density superimposed on the right heart border on frontal chest x-ray (CXR), most commonly due to mitral valve disease such as mitral stenosis or regurgitation, leading to left atrial dilatation.

Why is it called so?

It is named for the appearance of two overlapping densities on the right heart border: the usual right atrial shadow and a second distinct shadow from the enlarged left atrium extending posteriorly.

Pathophysiology

Chronic pressure or volume overload of the left atrium, typically from mitral stenosis or insufficiency, causes left atrial enlargement; the posteromedial portion of the enlarged left atrium projects behind the right atrium, creating a discrete second silhouette against the adjacent lung on the frontal projection while remaining hidden on lateral view.

Alternative names: Double density sign, Double right heart border sign

Other associated named signs: Widening of the carinal angle, third mogul sign (prominent left atrial appendage bulge along the left heart border), and the walking man sign, all further radiographic indicators of left atrial enlargement.

References

1. Nam JG et al. Automatic prediction of left cardiac chamber enlargement from chest radiographs using convolutional neural network. Eur Radiol. 2021.