A pleural effusion is a condition where excess fluid builds up around the lung, between the membrane that covers the lung and the membrane that lines the inside of the chest cavity (pleura). Normally, there are up to five teaspoons of fluid between the two pleural membranes, but this can increase and cause symptoms if too much fluid is produced, or if the rate of fluid removal decreases. A pleural effusion might be caused by heart failure, end-stage kidney disease, liver disease (cirrhosis), a pulmonary embolus, autoimmune conditions, infections, tumors or trauma. While a small pleural effusion that is free of infection or inflammation may not cause symptoms, a larger effusion or one that is infected can cause you to feel short of breath and have chest pain (especially when inhaling deeply, called "pleuritic chest pain"), fever or a cough.
In this article, we'll examine the basic idea of CAT scans. While the computer technology involved is fairly advanced, the fundamental concept at work is really very simple.
A pleural effusion can be diagnosed by ultrasound, as well as by physical examination, a chest X-ray or a CT scan. To diagnose fluid around the lungs using ultrasound, a probe is placed on the skin and images are formed when sound waves bounce off structures inside the body. A doctor can see these pictures on a screen and can see if the fluid around the lungs is free-flowing or, more seriously, if it is becoming thickened and hard. If there is only a small amount of fluid, the doctor can use ultrasound to help identify exactly where the effusion is located.
A small effusion may be left untreated, but for a larger, symptomatic one, doctors might drain the fluid by inserting a thin catheter over a needle into the pleural space, called thoracocentesis. Ultrasound guidance can be helpful, because it can allow the doctor to see exactly where the needle is going. Usually, a sample of the fluid is sent for analysis, to help doctors diagnose the underlying problem causing the build-up of fluid.