INFO/WWW: Surgical (subcutanous) emphysema may be caused by trauma to the thorax with leaking air into the soft tissue. A pneumothorax is an accumulation of air in the pleural space. Often spontaneous due to rupture of a pleural bleb. Other causes are trauma - also iatrogen CVC lines, asthma, TB, pneumonia and others. Pneumothorax will show as an area devoid of lung.
Pay attention tension pneumothorax. A tension pneumothorax results from leaking air into the pleural space on inspiration - but on expiration the leakage is closed by tissue or anything else. So the pressure in the pleural space increases on insparation - a clinical emergency. As the pressure in the pleural space arises, the surrounding structures, such as mediastinum, and heart can be displaced.