The pleura is a part of the mesothelium, a membrane that lines the chest and abdomen. The pleura lines the chest wall and wraps around the lungs providing a protective covering. This is the area where asbestos fibers can become embedded and cause mesothelioma. Other parts of the mesothelium surround the heart and the abdominal cavity. Malignancy can develop in the abdomen (peritoneal mesothelioma); in the membrane around the heart (pericardial mesothelioma); or in the lining on the outside of the lungs (pleural mesothelioma).
The lining on the chest wall is called the parietal pleura; the membrane wrapped around the lungs is known as the visceral pleura. These two membranes in the chest cavity are where seventy percent or more of all malignant mesothelioma cases develop. The term "effusion" is used for medical purposes to denote the abnormal buildup of fluid. Pleura effusion, then, is the development of excess fluid in the pleural space or pleural cavity – the area between the two pleural membranes.
Asbestos and Pleural Effusion
There is also a further division of the pleural mesothelium – that portion wrapped around the lungs is called the visceral pleura, while the lining of the chest wall is known as the parietal pleura. These two surfaces have a thin layer of liquid between them that provides lubrication during the breathing process; because the pleural surfaces are separated by fluid they do not rub together with every breath.
Asbestos fibers most often make their way into the human body through inadvertent inhalation. They are invisible to the eye and go unnoticed when inhaled in a cloud of industrial dust. Often they make their way through the lung wall and into the outer lining, or visceral pleura. As time passes, the fibers become an irritant and eventually cause the growth of deformed malignant cells that begin reproducing at an uncontrollable rate, causing inflammation of the pleura. This symptom often triggers the production of excess fluid in the area, resulting in pleural effusion. The malformed cells cause the pleural surfaces to thicken and an excess of fluid develops between them; these are the elements of pleural effusion.
This mesothelioma symptom is always asymmetrical; it develops on one side of the body or the other, impacting one lung or the other. Localized effusion is present in over 50% of all mesothelioma patients, and in a higher percentage of pleural mesothelioma victims.
Types of Pleural Effusion
There are two types of fluid that develop in the pleural area; one is called an exudate and the other a transudate. The first is associated with localized conditions such as cancer growth and the second with systemic failure such as congestive heart failure or cirrhosis. Exudative pleural effusion indicates that the medical problem may be a viral infection, pneumonia or a cancerous condition in the pleural area. If the medical problem is mesothelioma a tissue sample extracted through biopsy may confirm that the condition is malignant pleural effusion caused by cancerous mesothelial cells. Often fluid is extracted through a thoracentesis procedure by inserting a needle into the pleural cavity. This fluid can then be put through lab tests in order to find markers for malignant cells or for indicators of other types of disease.
Pleural Effusion Symptoms
Symptoms can vary for pleural effusion, from no discernable physical complications at all to extreme discomfort. Where there is substantial pleural effusion pressure on the lungs can lead to difficulty breathing unless in a sitting or standing position. Chest pain is a common symptom, usually a dull ache and often associated with the breathing process. On occasion pleural effusion and the displacement of pleural fluid can lead to friction rubbing between the two pleural membranes which can cause sharp chest pains. A dry cough can also be a common symptom of pleural effusion development.
Fatigue, swelling or fluid accumulation in the lower extremities, limited mobility and reduced appetite all can accompany the onset of pleural effusion. Treatment of the condition can become important as the effusion begins to take a significant toll on the quality of life, independent of any malignancy that may be causing it.
Pleural Effusion & Lung Cancer
Mesothelioma is not technically classified as lung cancer. It is cancer of the lining of the lungs, which in its late stages may lead to development of a tumor or tumors within the lung. Generally, pleural mesothelioma exhibits diffuse small tumors which cause the thickening of the pleural membrane and the development of exudative pleural effusion.
However pleural effusion with lung cancer is a standard pairing of symptom and diagnosis as well. Pleural effusion can also be symptomatic of pneumonia and other viral infections, which is one reason why mesothelioma is often not diagnosed until its late stages. It shares symptoms with a number of other, much more common diseases.
"Mesothelioma lung cancer" is a term that is often associated with pleural effusion; it should be noted that mesothlelioma also causes effusion, or fluid buildup, in those instances when it develops in the pericardial mesothelium around the heart or the peritoneal mesothelium on the abdominal wall. According to the National Cancer Institute, malignant pleural effusions are caused most commonly by carcinomas of the breast, lung, gastrointestinal tract or ovary and by lymphomas; they are common to many diseases.
While lung cancer may or may not cause malignant pleural effusion, the symptom will develop with pleural mesothelioma on virtually all occasions except those rare instances when the disease is treated in its early stages. Pairing asbestos with pleural effusion is unfortunately only one of many potential diagnoses and too often goes ignored until every other option is ruled out.
Treatment for Pleural Effusion
Withdrawal of the excess fluid can be accomplished through the use of a needle, but that does not stop recurrence of fluid buildup. One option is a procedure called pleurodesis which injects an agent between the two pleural membranes causing them to fuse and eliminate the space where fluid buildup occurs. This process can be extremely painful.
The surgical option is a pleurectomy, or removal of the two membranes. When this is done in conjunction with a diagnosis of malignant mesothelioma often the goal is also to remove malignant tissue. Medical imaging and biopsies are employed to determine what, if any, existence of malignant tissue exists. For the treatment of pleural effusion caused by a benign disease, a pleurectomy is not necessarily a superior choice over pleurodesis.
The third option is insertion of a tube to provide ongoing drainage of the pleural cavity. Some physicians see this as an excellent palliative treatment while managing the root cause of the pleural effusion. It is a symptom and condition associated with many serious human illnesses, all of which are more common than mesothelioma. For that reason research for more sophisticated treatment options continues.
- Mesothlelioma, Winston Tan MD, Mayo Medical School, Medscape, http://emedicine.medscape.com/article/280367-overview
- Frontline Assessment of Common Pulmonary Presentations, National Lung Health Education Project, http://www.nlhep.org/books/pul_Pre/pleural-effusion.html
- Malignant Pleural Effusions PDQ, National Cancer Institute, http://www.cancer.gov/cancertopics/pdq/supportivecare/cardiopulmonary/Patient/page3
- Management of Malignant Pleural Effusion and Ascites… Inan, DeSousa et al, World Journal of Surgical Oncology, August 2008