Pericardial fat tag sign (pneumothorax)

The pericardial fat tag sign is a sign of pneumothorax on supine CXR where the cardiac border has a lumpy contour.

When gas is located in the pleural space between the lung and mediastinum, the pericardial fat is no longer compressed against the mediastinum and therefore can hang or dangle laterally, giving a lumpy or mogul appearance to the cardiac border/s.

It is not commonly seen and may be seen in the absence or presence of all the other chest x-ray signs of a supine pneumothorax.