Pulmonary effusion is actually a common name for what is clinically known as pleural effusion. There are many causes of pleural effusion, and its severity needs to be analyzed in the context of specific situations. Pleural effusion next to pneumonia is the most common type of pleural effusion, mostly due to pleural exudation caused by pneumonia, and is usually not serious. Tuberculous pleural effusion is also common and is caused by tuberculosis, which is a relatively serious condition that can be prolonged if left untreated. Connective tissue diseases can also cause pleural effusion, such as rheumatoid arthritis and erythromelalgia, which are also relatively serious and require active treatment of the primary disease. Malignant tumors of the lung and pleura, resulting in more serious pleural effusion, often indicate the existence of metastasis of the tumor and should be actively treated. When pleural effusion occurs, it is recommended that you should go to the respiratory medicine department of the hospital in time to have the doctor determine the cause of the effusion and provide symptomatic treatment. When the amount of fluid accumulation is large, thoracentesis treatment is needed to extract excessive fluid.