Pneumothorax: a collection of air within the pleural cavity, arising either from the outside or from the lung. Pneumothoraces may be traumatic, iatrogenic, or spontaneous. A tension pneumothorax is a particular type of pneumothorax where the air may enter (though a defect of the chest wall, lung, or airways) on inspiration, but cannot exit on expiration. Each breath increases the amount of trapped air in the chest cavity, leading to further lung compression. This is often an urgent situation and may progress to a medical emergency if there is compromise of the venous return to the heart causing hypotension and rarely shock.
Pleural plaques: discrete fibrous or partially calcified thickened area which can be seen on X-rays of individuals exposed to asbestos. Although pleural plaques are themselves asymptomatic, in some patients this develops into pleural thickening.