X-ray showing the left lung (right of image) affected by pneumothorax, a condition in which air enters the pleural cavity. The lung collapses and shrinks towards the centre of the rib cage, visible as a faint shadow running downwards at right. Treatment involves the removal of the air through a suction tube (extreme right) which is kept in place for several days. Pneumothorax may occur spontaneously, or as a complication of a lung disease, or it may follow an injury such as a fractured rib. If there is continual leakage of air pneumothorax may become fatal because of compression on the heart.