Fallen lung sign

The fallen lung sign (also known as CT fallen lung sign) describes the appearance of collapsed lung away from the mediastinum encountered with tracheobronchial injury (in particular those >2 cm away from the carina). It is helpful to look for this rare but specific sign, in cases of unexplained persistent pneumothorax. It can be seen on both plain radiographs and CT.

History and etymology

The sign was first described in a 1970 case report as the lung falling away from the mediastinum when the bronchus is completely transected, and the vascular structures of the hilum remain intact.