Pleural effusion is a medical condition characterized by the buildup of excess fluid between the layers of the pleura outside the lungs. The pleura are thin membranes that line the lungs and chest cavity. Normally, only teaspoons of watery fluid are in the pleural space, which allows the lungs to move smoothly in the chest cavity when breathing. Pleural effusion can occur by itself or can be the result of surrounding parenchymal disease like infection, malignancy, or inflammatory conditions.

The seriousness of the condition depends on the primary cause of pleural effusion, whether breathing is affected, and whether it can be treated effectively. Some patients with pleural effusion have no symptoms, with the condition discovered on a chest x-ray that is performed for another reason. The patient may have unrelated symptoms due to the disease or condition that has caused the effusion. Symptoms of pleural effusion include shortness of breath, chest pain, cough, fever, and difficulty breathing.

A wide range of things can cause a pleural effusion, including congestive heart failure, pneumonia, malignancy, and pulmonary embolism. Certain medications, abdominal surgery, and radiation therapy may also cause pleural effusions. Pleural effusion may occur with several types of cancer including lung cancer, breast cancer, and lymphoma. In some cases, the fluid itself may be malignant (cancerous), or may be a direct result of chemotherapy.

The tests most commonly used to diagnose and evaluate pleural effusion include chest x-ray, CT scan, ultrasound, and thoracentesis. Treatment for pleural effusion depends on the underlying cause. Causes of pleural effusion that can be effectively treated or controlled include an infection due to a virus, pneumonia, or heart failure. Treatment may involve draining the fluid from the pleural space using a needle or catheter, treating the underlying condition, or both.