Pneumothorax is a lung anomaly in which rushing air fills in the pleural space when it is opened from the outside, causing a part of the lung to cave in. In this case the lung no longer follows movement of the thorax and the diaphragm (external pneumothorax). This also occurs if there is a tear in the lung and the visceral pleura and air is able to pass from the respiratory pathways into the pleural space (internal pneumothorax); in this case the mediastinum is pulled toward the healthy side during inspiration, and toward the diseased side during expiration. After closure of the tear, air in the pleural space is reabsorbed within a few days. Pneumothorax can be caused by trauma or can occurs spontaneously by unknown reason.