Most pleural effusions are caused by inflammation of the pleura, whether it is tuberculous pleurisy or pleurisy caused by common infection, there is inflammation of the mural pleura and the dirty pleura. The pathological changes of inflammation are metaplasia, exudation and hyperplasia. Once the pleura becomes inflamed, there is fibrin exudation, exudate to the pleural cavity, granulation tissue hyperplasia, and secondary thickening of the pleura. Generally, limited pleural thickening has relatively little effect on respiratory function and does not require treatment. Extensive pleural thickening can affect respiratory function and requires pleurodesis, which involves stripping the dirty pleura and the wall pleura to facilitate lung reopening.