A pleural effusion is a build-up of fluid between the layers of the membrane that lines the lungs.
Ordinarily, there is only 15 to 20cc of fluid in this space which is known as the pleural cavity.
Symptoms include cough, shortness of breath, and chest pain that worsens with coughing.
With lung cancer, people sometimes develop a pleural effusion that contains cancer cells. This is known as a malignant pleural effusion.