Light micrograph of a section through human lung tissue showing fibrinous pleurisy. Pleuritis and pleurisy are the same thing and describe inflammation of the pleural tissue that surrounds the outside of both lungs and lines the inside of the chest cavity. There is a small amount of fluid in the small space between the two layers. When the tissue becomes inflamed, the two layers rub together causing pain in the chest. Pleuritis may be benign, but it can also be caused by pleural mesothelioma (an asbestos-related cancer).