The "fallen lung with absent hilum" signs of complete bronchial transection.

A 19-year-old pedestrian who was the victim of a motor vehicle accident had a left pneumothorax with a large air leak. Despite a well-placed chest tube, a chest radiograph showed that the left lung had fallen down and away from the mediastinum and that no hilar structures were visible. This "fallen lung with an absent hilum" is considered virtually diagnostic of complete mainstem bronchus transection.