What sort of disease is a collapsed lung?

Lung collapse: A collapsed lung can be spontaneous and associated with a variety of diseases (emphysema for example or alpha-1- antitrypsin deficiency) or traumatic. Various conditions can result in which if untreated the lung may remain collapsed or produce a tension pneumothorax demanding emergent treatment.

Pneumothorax: A leak of air from a lung can fill the pleural cavity, the normally-empty sac around it. This air does not allow the lung to expand, collapsing it. A chest tube or pigtail will drain the air until the leak seals. Causes are ruptured blebs from emphysema, trauma from rib fractures or central line placement, mechanical ventilation, or unknown. Recurrent pneumothoraces may need lung surgery.

Air in wrong place: Pneumothorax is an accumulation of air outside your lung but inside your chest. It is commonly described as a "collapsed lung" because the air in this space displaces your lung and prevents complete expansion of your lung.