Pneumothorax on an erect chest radiograph is easy to diagnose, but on supine films it is difficult because air in the pleural cavity takes a non dependent position.
Signs of pneumothorax on supine radiographs are:
-
deep sulcus sign: air in the pleural cavity collects in the anterolateral pleural space outlining the deep costophrenic angle
- increased clarity or sharpness of the ipsilateral hemidiaphragm
- double diaphragm sign
- increased sharpness of the mediastinal or cardiac outline