Pleural Mesothelioma
Pleural mesothelioma is a form cancer that is almost always caused by asbestos exposure and is most commonly found in the outer lining of the lungs called the mesothelium. Pleural mesothelioma is the most common type of mesothelioma and has been studied to a far greater degree than any of the other forms of the disease. The vast majority of treatment options and all of the staging guidelinescurrently utilized in the diagnosis of mesothelioma are based on pleural mesothelioma. Because of this, when most people speak of “mesothelioma,” they are usually speaking of malignant pleural mesothelioma. After pleural mesothelioma, peritoneal mesothelioma accounts for the majority of other diagnoses. Although ongoing research is being conducted to find a cure, or cures, for mesothelioma, all types are still considered to be incurable in the medical community.
Function of the Pleura
Pleural mesothelioma occurs when one of the pleura in the chest cavity becomes malignant. The pleurae are serous membranes, which mean they secrete a lubricating fluid, called serous fluid. There are two pleurae in the chest cavity and their job is to protect and cushion the lungs by secreting fluid that allows the lungs to move smoothly within the chest cavity when breathing. While they certainly serve an important purpose, each pleura can be removed if it becomes damaged or diseased. The ease of which it can be removed is dependent on which of the pleural surfaces becomes malignant: the parietal pleura or the visceral pleura.
The parietal pleura lines the inside of the chest and covers the ribs and the pericardium. It is a fairly thin tissue between two and three millimeters thick and is the more easily removed of the two pleural surfaces. At a single millimeter in thickness, the visceral pleura is barely half the width of the parietal pleura. It directly covers the lung itself, which makes extraction of the visceral pleura without subsequent damage to the lung very difficult.
Development of Pleural Mesothelioma
While science has conclusively shown that mesothelioma is caused only by asbestos exposure, the actual biological processes by which it develops are still being investigated. In essence though, pleural mesothelioma develops when jagged asbestos fibers are inhaled and settle in and around the lungs. The fibers become lodged in its small passageways and in the surface of its lining. The body’s immune system is able to process and breakdown some of these asbestos fibers, but invariably many still remain. Over time, the fibers cause chronic inflammation, the development of pleural fibroses (a thickening of the pleural surfaces) and pleural effusions (buildup of fluid in the pleural spaces) and in many people, cancerous cell development. If the fibers create a malignancy in the lung itself, one is diagnosed with lung cancer. If the malignancy begins in one of the pleural tissues, one is diagnosed with pleural mesothelioma.
It is because of the proximity of the pleurae to the lung that many people mistakenly think of pleural mesothelioma as a form of lung cancer. While a pleural malignancy can invade the lung, the tumor’s origin site is still the pleura, so pleural mesothelioma should never be treated as lung cancer.
