Pleural effusion occurs when too much fluid collects in the pleural space (the space between the two layers of the pleura). It is commonly known as "water on the lungs." It is characterized by shortness of breath, chest pain, gastric discomfort (dyspepsia ), and cough.
There are two thin membranes in the chest, one (the visceral pleura) lining the lungs, and the other (the parietal pleura) covering the inside of the chest wall. Normally, small blood vessels in the pleural linings produce a small amount of fluid that lubricates the opposed pleural membranes so that they can glide smoothly against one another during breathing movements. Any extra fluid is taken up by blood and lymph vessels, maintaining a balance. When either too much fluid forms or something prevents its removal, the result is an excess of pleural fluid—an effusion. The most common causes are disease of the heart or lungs, and inflammation or infection of the pleura.
Pleural effusion itself is not a disease as much as a result of many different diseases. For this reason, there is no "typical" patient in terms of age, sex, or other characteristics. Instead, anyone who develops one of the many conditions that can produce an effusion may be affected.
There are two types of pleural effusion: the transudate and the exudate. This is a very important point because the two types of fluid are very different, and which type is present points to what sort of disease is likely to have produced the effusion. It also can suggest the best approach to treatment.
A transudate is a clear fluid, similar to blood serum, that forms not because the pleural surfaces themselves are diseased, but because the forces that normally produce and remove pleural fluid at the same rate are out of balance. When the heart fails, pressure in the small blood vessels that remove pleural fluid is increased and fluid "backs up" in the pleural space, forming an effusion. Or, if too little protein is present in the blood, the vessels are less able to hold the fluid part of blood within them and it leaks out into the pleural space. This can result from disease of the liver or kidneys, or from malnutrition.
An exudate—which often is a cloudy fluid, containing cells and much protein—results from disease of the pleura itself. The causes are many and varied. Among the most common are infections such as bacterial pneumonia and tuberculosis; blood clots in the lungs; and connective tissue diseases, such as rheumatoid arthritis. Cancer and disease in organs such as the pancreas also may give rise to an exudative pleural effusion.
Special types of pleural effusion
Some of the pleural disorders that produce an exudate also cause bleeding into the pleural space. If the effusion contains half or more of the number of red blood cells present in the blood itself, it is called hemothorax. When a pleural effusion has a milky appearance and contains a large amount of fat, it is called chylothorax. Lymph fluid that drains from tissues throughout the body into small lymph vessels finally collects in a large duct (the thoracic duct) running through the chest to empty into a major vein. When this fluid, or chyle, leaks out of the duct into the pleural space, chylothorax is the result. Cancer in the chest is a common cause.
Causes and symptoms
Causes of transudative pleural effusion
Among the most important specific causes of a transudative pleural effusion are:
- Congestive heart failure. This causes pleural effusions in about 40% of patients and is often present on both sides of the chest. Heart failure is the most common cause of bilateral (two-sided) effusion. When only one side is affected it usually is the right (because patients usually lie on their right side).
- Pericarditis. This is an inflammation of the pericardium, the membrane covering the heart.
- Too much fluid in the body tissues, which spills over into the pleural space. This is seen in some forms of kidney disease ; when patients have bowel disease and absorb too little of what they eat; and when an excessive amount of fluid is given intravenously.
- Liver disease. About 5% of patients with a chronic scarring disease of the liver called cirrhosis develop pleural effusion.
Causes of exudative pleural effusions
A wide range of conditions may be the cause of an exudative pleural effusion:
- Pleural tumors account for up to 40% of one-sided pleural effusions. They may arise in the pleura itself (mesothelioma ), or from other sites, notably the lung.
- Tuberculosis in the lungs may produce a long-lasting exudative pleural effusion.
- Pneumonia affects about three million persons each year, and four of every ten patients will develop pleural effusion. If effective treatment is not provided, an extensive effusion can form that is very difficult to treat.
- Patients with any of a wide range of infections by a virus, fungus, or parasite that involve the lungs may have pleural effusion.
- Up to half of all patients who develop blood clots in their lungs (pulmonary embolism ) will have pleural effusion, and this sometimes is the only sign of embolism.
- Connective tissue diseases, including rheumatoid arthritis, lupus, and Sjögren's syndrome may be complicated by pleural effusion.
- Patients with disease of the liver or pancreas may have an exudative effusion, and the same is true for any patient who undergoes extensive abdominal surgery. About 30% of patients who undergo heart surgery will develop an effusion.
- Injury to the chest may produce pleural effusion in the form of either hemothorax or chylothorax.
The key symptom of a pleural effusion is shortness of breath. Fluid filling the pleural space makes it hard for the lungs to fully expand, causing the patient to take many breaths so as to get enough oxygen. When the parietal pleura is irritated, the patient may have mild pain that quickly passes or, sometimes, a sharp, stabbing pleuritic type of pain. Some patients will have a dry cough. Occasionally a patient will have no symptoms at all. This is more likely when the effusion results from recent abdominal surgery, cancer, or tuberculosis. Tapping on the chest will show that the usual crisp sounds have become dull, and on listening with a stethoscope the normal breath sounds are muted. If the pleura is inflamed, there may be a scratchy sound called a "pleural friction rub."
When pleural effusion is suspected, the best way to confirm it is to take chest x rays, both straight-on and from the side. The fluid itself can be seen at the bottom of the lung or lungs, hiding the normal lung structure. If heart failure is present, the x-ray shadow of the heart will be enlarged. An ultrasound scan may disclose a small effusion that caused no abnormal findings during chest examination. A computed tomography scan is very helpful if the lungs themselves are diseased.
In order to learn what has caused the effusion, a needle or catheter is often used to obtain a fluid sample, which is examined for cells and its chemical make-up. This procedure, called a thoracentesis, is the way to determine whether an effusion is a transudate or exudate, giving a clue as to the underlying cause. In some cases—for instance when cancer or bacterial infection is present—the specific cause can be determined and the correct treatment planned. Culturing a fluid sample can identify the bacteria that cause tuberculosis or other forms of pleural infection. The next diagnostic step is to take a tissue sample, or pleural biopsy, and examine it under a microscope. If the effusion is caused by lung disease, placing a viewing tube (bronchoscope) through the large air passages will allow the examiner to see the abnormal appearance of the lungs.
The best way to clear up a pleural effusion is to direct treatment at what is causing it, rather than treating the effusion itself. If heart failure is reversed or a lung infection is cured by antibiotics, the effusion will usually resolve. However, if the cause is not known, even after extensive tests, or no effective treatment is at hand, the fluid can be drained away by placing a large-bore needle or catheter into the pleural space, just as in diagnostic thoracentesis. If necessary, this can be repeated as often as is needed to control the amount of fluid in the pleural space. If large effusions continue to recur, a drug or material that irritates the pleural membranes can be injected to deliberately inflame them and cause them to adhere close together—a process called sclerosis. This will prevent further effusion by eliminating the pleural space. In the most severe cases, open surgery with removal of a rib may be necessary to drain all the fluid and close the pleural space.
When the cause of pleural effusion can be determined and effectively treated, the effusion itself will reliably clear up and should not recur. In many other cases, sclerosis will prevent sizable effusions from recurring. Whenever a large effusion causes a patient to be short of breath, thoracentesis will make breathing easier, and it may be repeated if necessary. To a great extent, the outlook for patients with pleural effusion depends on the primary cause of effusion and whether it can be eliminated. Some forms of pleural effusion, such as that seen after abdominal surgery, are only temporary and will clear without specific treatment. If heart failure can be controlled, the patient will remain free of pleural effusion. If, on the other hand, effusion is caused by cancer that cannot be controlled, other effects of the disease probably will become more important.
Culture— A test that exposes a sample of body fluid or tissue to special material to see whether bacteria or another type of microorganism is present.
Dyspepsia— A vague feeling of being too full and having heartburn, bloating, and nausea. Usually felt after eating.
Exudate— The type of pleural effusion that results from inflammation or other disease of the pleura itself. It features cloudy fluid containing cells and proteins.
Pleura or pleurae— A delicate membrane that encloses the lungs. The pleura is divided into two areas separated by fluid-the visceral pleura, which covers the lungs, and the parietal pleura, which lines the chest wall and covers the diaphragm.
Pleural cavity— The area of the thorax that contains the lungs.
Pleural space— The potential area between the visceral and parietal layers of the pleurae.
Pneumonia— An acute inflammation of the lungs, usually caused by bacterial infection.
Sclerosis— The process by which an irritating material is placed in the pleural space in order to inflame the pleural membranes and cause them to stick together, eliminating the pleural space and recurrent effusions.
Thoracentesis— Placing a needle, tube, or catheter in the pleural space to remove the fluid of pleural effusion. Used for both diagnosis and treatment.
Transudate— The type of pleural effusion seen with heart failure or other disorders of the circulation. It features clear fluid containing few cells and little protein.
Because pleural effusion is a secondary effect of many different conditions, the key to preventing it is to promptly diagnose the primary disease and provide effective treatment. Timely treatment of infections such as tuberculosis and pneumonia will prevent many effusions. When effusion occurs as a drug side-effect, withdrawing the drug or using a different one may solve the problem. On rare occasions, an effusion occurs because fluid meant for a vein is mistakenly injected into the pleural space. This can be prevented by making sure that proper technique is used.
National Heart, Lung and Blood Institute. P.O. Box 30105, Bethesda, MD 20824-0105. (301) 251-1222. 〈http://www.nhlbi.nih.gov〉.
"Pleural Effusion." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. (June 26, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/pleural-effusion
"Pleural Effusion." Gale Encyclopedia of Medicine, 3rd ed.. . Retrieved June 26, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/pleural-effusion
Pleural effusion is the accumulation of fluid in the pleural space. The pleural space is the region between the outer surface of each lung (visceral pleurae) and the membrane that surrounds each lung (parietal pleurae). Under normal conditions, the pleurae are kept wet with pleural fluid to allow movement of the lungs within the chest. The pleural fluid comes from cells that make up the pleurae. Pleural fluid is continuously being produced and removed, a process that is precisely controlled by many factors. Cancer can interfere with this delicate balance within the pleural space causing fluid to accumulate.
Cancer is responsible for 40% of all pleural effusions, which are then called malignant pleural effusions. Pleural effusion is the first symptom of cancer for up to 50% of the patients. Thirty-five percent of the cases of malignant pleural effusion are caused by lung cancer, 23% by breast cancer , and 10% by lymphoma .
Chest x rays and computed topography scans may be performed to diagnose pleural effusion. Thoracentesis , the removal of pleural fluid through a long needle, is usually performed for diagnostic purposes. Fluid removed by thoracentesis will be sent to the lab to be thoroughly evaluated. Thoracoscopy , in which a wand-like lighted camera (endoscope) is inserted through the chest, may be conducted to diagnose pleural effusion. During thoracoscopy, samples (biopsy ) of pleura may be taken.
Pleural effusion can hinder the normal function of the lungs. Symptoms of pleural effusion include chest pain, chest heaviness, breathing difficulties, and a dry cough. Patients with malignant pleural effusions tend to be weak and have a short-span life expectancy. The prognosis depends on the type of cancer. Sixty-five percent of patients with malignant pleural effusions die within three months and 80% die within six months. However, patients with pleural effusion related to breast cancer have a longer life expectancy.
Malignant pleural effusions are most often associated with lymphomas, leukemia, breast cancer, gastrointestinal cancer, lung cancer, and ovarian cancer . For the majority of patients, pleural effusion occurs in the lung on the same side as the cancer. For one third of the patients, pleural effusion occurs in both lungs.
Pleural effusion in cancer patients can be caused by several different conditions. Blockage of the lymphatic system, a series of channels for drainage of body fluids, interferes with the removal of pleural fluid. Blockage of the veins of the lungs increases the pressure at the pleurae which causes fluid accumulation. Cancerous cells may seed onto pleurae and cause inflammation which increases fluid in the pleural space. High numbers of cancerous cells may collect in the pleural space (tumor cell suspensions) which causes extra fluid to be released. Accumulation of fluid in the abdominal cavity may cross over to the pleural space.
Management of pleural effusion strives to relieve symptoms and improve quality of life. Cure is not always possible. The treatment method depends on the patient's age, prognosis, and location of the first tumor. Treatment for patients with pleural effusion who are asymptomatic (do not have symptoms) consists solely of observation.
Treatment options for pleural effusion include:
- Thoracentesis. Removal of the excess pleural fluid often relieves the symptoms of pleural effusion. However, effusion usually recurs within a few days. Repeat thoracentesis is not recommended, unless the patient has end-stage disease.
- Tube thoracostomy. A tube is inserted through the chest and into the pleural space to drain pleural fluid. When used alone, recurrence is very common.
- Indwelling pleural catheters. A thin flexible tube (catheter) is placed between the pleural cavity and the chest skin to allow drainage of pleural fluid. This method allows for continual drainage of pleural fluid without much pain.
- Pleurodesis . After tube thoracostomy, one of any number of chemicals (sclerosing agents) is put into the pleural space to cause the visceral and parietal pleurae to stick together. Chemical pleurodesis is considered to be the treatment of choice for patients with malignant pleural effusion.
- Pleurectomy. Surgical removal of the parietal pleura through an incision in the chest wall (thoracotomy ) is nearly 100% effective. Pleurectomy is not routinely performed and is reserved for patients for whom other treatments have failed. To be eligible for pleurectomy, the patient must have a long life expectancy and be able to tolerate major surgery.
- Pleuroperitoneal shunt. This procedure places a rubber tube between the pleural space and the abdominal cavity. A pump is used to move excess fluid out of the pleural space and into the abdominal cavity, where it would be absorbed. The patient must press the pump for several minutes four times daily. Although not frequently used, this is an effective treatment for cases that failed tube thoracostomy and pleurodesis.
- External radiation. Patients who have pleural effusion caused by blockage of a lymph duct may be treated by radiation therapy . External radiation therapy is successful for patients with pleural effusion related to lymphoma.
- Supportive care. Patients with end-stage cancer may not receive treatment for pleural effusion. Pain medications and oxygen therapy can be provided to keep the patient comfortable.
Belinda Rowland, Ph.D.
—The membrane that surrounds each lung.
—The space between the visceral and parietal pleurae.
—The outer surface of each lung.
"Pleural Effusion." Gale Encyclopedia of Cancer. . Encyclopedia.com. (June 26, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/pleural-effusion-0
"Pleural Effusion." Gale Encyclopedia of Cancer. . Retrieved June 26, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/pleural-effusion-0