Pleurisy. X-rays of the lungs of a 65 year old patient with pleurisy, an inflammation of the membranes (pleura) that line the chest cavity and lungs. In the left image, a large area of inflammation (white mass at centre left) is obstructing the patient's right lung. Inflammation of the pleura leads to the lungs rubbing against the chest wall, which causes sharp pain on breathing. In this case, fluid had accumulated in the space between the membranes, causing breathing difficulties, so the lung needed to be drained to remove it. The right image shows the lung after drainage of the fluid. The underlying cause also needs to be treated, which may be a bacterial infection, viral infection, cancer or an embolism.