The presence of excessive fluid in the pleural cavity for any reason is called pleural effusion, commonly known as pleural fluid. Pleural effusion is a clinical symptom with a variety of causes including infection, tumor, trauma and other diseases. Normally, there are 5 to 15 ml of fluid in the pleural cavity, which acts as a lubricant when breathing. The formation and absorption of 500-1000 ml of fluid in the pleural cavity every day. A variety of diseases can lead to increased production and decreased absorption of fluid in the pleural cavity, resulting in pleural effusion. Pleural effusions are divided into leaky pleural effusions and exudative pleural effusions. Common disease causes of pleural effusions, common disease causes of leaky pleural effusions, such as pleural effusions caused by cirrhosis, superior vena cava syndrome, nephrotic syndrome, glomerulonephritis, mucinous edema from dialysis, etc. The common underlying causes of exudative pleural effusion, such as malignant tumors of the pleura, connective tissue diseases such as systemic lupus erythematosus, lymphoma, myeloma, etc.; infections of the chest and lung, such as bacterial, viral, fungal, parasitic, mycobacterium tuberculosis infections; diseases of the digestive system, such as liver abscess, esophageal rupture, viral hepatitis, etc.; drugs can cause pleural diseases, such as bromocriptine, levodopa, etc.. Others are caused by diseases such as hemothorax, uremia, endometrial displacement, and radioactive injury. The clinical manifestations of pleural effusion are chest tightness, dyspnea, pain, symptoms of the primary disease, etc. Pleural effusion is mainly detected by clinical signs and symptoms, imaging, chest ultrasound, CT MRI, etc., and also by thoracentesis and fluid aspiration.