Effusion is an increase in fluid in the plasma cavity of the body. If the fluid appears in the chest cavity, it is called pleural effusion; if it appears in the abdominal cavity, it is called peritoneal effusion; if it appears in the pelvic cavity, it is called pelvic effusion; if it appears in the joint cavity, it is called joint effusion. What is pleural effusion? Pleural effusion is a pathological phenomenon called pleural effusion in which the fluid in the chest cavity is produced excessively or absorbed less for any reason, causing the fluid in the chest cavity to exceed the normal range. The causes that can lead to pleural effusion include infectious diseases, circulatory system diseases, tumors, hypoproteinemia, trauma, hemopneumothorax, etc.