Pleural Effusion (Fluid in the Lungs) is the medical term for when too much fluid collects between the tissue layers that line your lungs and your chest. A certain amount of fluid is normal and necessary, but excessive amounts can be caused by certain diseases and conditions, such as mesothelioma.
A pleural effusion (fluid in the lungs) that's caused by abnormal lung pressure—congestive heart failure is a typical cause—produces watery fluid (transudative). A pleural effusion that develops because the pleura (the surface linings of the lungs) are inflamed and swollen is often a result of a serious lung problem such as lung cancer, mesothelioma, infections like tuberculosis, drug reactions, or asbestosis disease. These produce fluid that's full of protein (exudative).
Fluid build-up is one of mesothelioma's symptoms. It will occur in whatever area of the body the cancer strikes—in the lungs it is pleural mesothelioma and produces excess pleural fluid. In the abdomen (peritoneum) it produces ascites fluid in the peritoneum.
Your abdomen is lined with a double layer of tissue called the peritoneum. One of its layers covers the wall of your abdomen. The other protects the organs inside your abdomen. Normal amounts of peritoneal fluid help lubricate your abdominal organs so they can move around inside. But when too much of this fluid builds up between the two layers, and/or the peritoneal fluid is found to contain infection, it's called ascites fluid, and causes a condition similar to a Pleural Effusion (Fluid in the Lungs).
When the amount of fluid present between the layers of the peritoneum or in the lungs or around the heart becomes excessive, it's called ascites fluid and indicates a Pleural Effusion (Fluid in the Lungs) problem—an infection or possibly a disease such as mesothelioma or other cancer. If you are having chest or abdominal discomfort and doctors notice that you have ascites fluid accumulating, they will want to withdraw some of this fluid to test for microorganisms. A test of ascites fluid is not necessarily sufficient, though. Your doctor will want to perform additional tests before making a diagnosis.