The protective tissue that covers serous membranes of the lungs, heart, and abdominal organs is called the mesothelium. Depending on its location, the mesothelium may be called as the pleura¬, the membrane surrounding the lungs; pericardium, the sac that protects the heart; and the peritoneum, the membrane that lines the abdominal organs. When a person has mesothelioma or the cancer of the mesothelium, the organs mentioned above are most likely affected.
It has been suggested that the pathogenesis of mesothelioma begins when a person inhales asbestos fibers that may lodge deep into the lungs that may penetrate the pleural linings. This deposition of the asbestos fibers is recognized by the immune system that causes the attraction of macrophages (special types of white blood cells) leading to localized inflammation and cellular changes. This will eventually lead to the formation of a malignant tumor that is very difficult to treat.
There are 3 types of mesothelioma, pericardial, pleural, and peritoneal mesothelioma. Basically, it is a similar disease process but the symptoms may vary because of its distinct location. There is also a possibility that various types may occur simultaneously.
Pleural mesothelioma means that the tumour arises from the pleura or the delicate membrane enclosing the lungs. The pleura can be divided into two layers–the visceral pleura, the layer that covers the lung, and the parietal pleura, which line the chest wall. In between, there is a space that holds a small volume of fluid that serves as a lubricant, making it possible for the two layers to slide efficiently over each other as the lungs expand and contract with each respiration.
Because of lung involvement, pleural mesothelioma manifests as lung problems. The person may experience pleural effusion, or the abnormal accumulation of fluid in the spaces between the two layers of pleural membrane. This may manifest as shortness of breath, non-productive cough, chest wall pain, and difficulty of breathing. Mesothelioma that affects the pleura may also cause fever, fatigue, blood in the sputum, anemia, and subsequent weight loss.
Majority of mesothelioma cases affects the pleura, making up 70% of all mesothelioma.
Mesothelioma that develops in the membrane that lines the entire abdominal cavity is termed as peritoneal mesothelioma. Also known as abdominal mesothelioma, this type of cancer may cause severe abdominal pain and swelling due to the build up of intraperitoneal fluid within the peritoneal membrane called, ascites. This may also cause fever and increase in abdominal girth. A person may experience changes in bowel habits such as diarrhea and constipation which will eventually lead to weight loss.
Typically, the manifestations of mesothelioma appear 20 to 50 following exposure to asbestos.
Another type of mesothelial tissue is found on the sac covering the heart for protection and lubrication. This is called the pericardium.
Similar to the abovementioned mesothelial tissues, the pericardium may also become affected with mesothelioma. This type is very deadly as this already involves the major organ of circulation. However, this form of mesothelioma is very uncommon and makes up about 1-5% of the total diagnosed cases.
The development of pericardial mesothelioma is not clearly understood. One theory is that asbestos particles may be transported from the lungs to the bloodstream which may lodge to the linings of the heart and cause chronic inflammation leading to cancerous tumour growth. This may cause rapid expansion of the pericardial sac resulting to the accumulation of fluid called pericardial effusion. A person may experience chest pain, palpitations, irregular heart beat (arrhythmia), and some degree of difficulty of breathing. The cancerous growths may also metastatize (spread) to nearby organs such as the lungs.
The special thing about mesothelioma is that this cancer has a specific cause–asbestos.
Exposure to asbestos, may it be from one’s occupation, environment, and asbestos products, has been considered a major risk factor for the development of mesothelioma.
Working in the asbestos industry has posed a number of health risks for the workers and their families. Several illnesses have already been linked to asbestos inhalation such as lung and throat cancer, gastrointestinal tumors, diffuse pleural thickening, mesothelioma, and asbestosis. Family members of workers in asbestos factories also have an increased risk of developing these ailments because of the dust particles that may have settled in the worker’s clothing and hair.
Asbestos has been widely used around the globe because of its useful properties. It is present in a wide array of materials such as vinyl asbestos tile, drywall jointing compounds, plaster, cement panels, brakes pads, shoes, insulation in floors, ceiling, pipes, ducts, and walls, fireproofing, gaskets and many more products. Through these materials, the public may be put at risk for asbestos exposure. A good example for this is the destruction of the World Trade Center that was thought to release a lot of asbestos particles in the air. But even without such happenings, as long as asbestos exists in home and building materials, people are being killed silently.
Because of the long-term and fatal effects of asbestos and to put to an end the damages caused by asbestos to people, it has been banned by many countries including Australia (2003), France (1997), Italy (1992), Japan (2004), New Zealand (1984), and United Kingdom (2006). Several nations and environmental groups have also imposed policies and controls in asbestos handling and disposal.