Pleural Disorders

Your pleura is a large, thin sheet of tissue that wraps around the outside of your lungs and lines the inside of your chest cavity. Between the layers of the pleura is a very thin space. Normally it's filled with a small amount of fluid. The fluid helps the two layers of the pleura glide smoothly past each other as your lungs breathe air in and out.
Disorders of the pleura include

Pleurisy - inflammation of the pleura that causes sharp pain with breathing
Pleural effusion - excess fluid in the pleural space
Pneumothorax - buildup of air or gas in the pleural space
Hemothorax - buildup of blood in the pleural space

Many different conditions can cause pleural problems. Viral infection is the most common cause of pleurisy. The most common cause of pleural effusion is congestive heart failure. Lung diseases, like chronic obstructive pulmonary disease (COPD), tuberculosis, and acute lung injury, cause pneumothorax. Injury to the chest is the most common cause of hemothorax. Treatment focuses on removing fluid, air, or blood from the pleural space, relieving symptoms, and treating the underlying condition.

NIH: National Heart, Lung, and Blood Institute