Mesothelium is the anatomical term for a thin membrane surrounding the organs of the chest and abdomen(the plural is mesothelia). The mesothelium surrounding the lungs is more specifically called the pleura. We also have a mesothelium surrounding the heart (the pericardium) and a mesothelium surrounding the abdominal organs (the peritoneum).
In all cases, these membranes consist of two thin layers. The inner layer is wrapped closely around the organ it surrounds, and the outer layer provides a larger sac inside which the organs can move. To make it easier for organs to move freely, the area between the two layers is filled with a lubricating fluid.
Approximately 70% of mesothelioma tumors are found in the pleura, while approximately 20% are in the peritoneum and 10% in the pericardium. In exceptionally rare cases, a tumor may occur in an extension of the peritoneum surrounding the testes, called the tunica vaginalis. 
How Pleural Mesothelioma Occurs
Asbestos is a naturally occurring mineral made up of needle-like fibers. Mining or manufacturing processes frequently release tiny fragments of these fibers into the air as dust where they can be inhaled.
Because the asbestos dust particles are so fine, they escape many of the body’s defense mechanisms designed to keep foreign materials out of the lungs. Defenses such as hair and moisture in the nose, cilia (fine, hair-like structures in the bronchial tubes that trap and move foreign materials upward), and the involuntary cough response all fail to keep the asbestos fibers out.
Ultimately, the fine fibers make their way into the lungs’ tiny air sacs (alveoli) where blood cells give off carbon dioxide and absorb oxygen from the air. Being very small and very hard, a fiber can puncture the alveoli’s exceptionally thin cell walls and trigger the body’s immune system response.
Macrophages, the immune system cells designed to surround and digest invaders, have no effect on the asbestos mineral fibers. Worse, in an attempt to destroy the asbestos, the macrophages themselves are destroyed, which releases their specialized toxins and further damages the alveoli. This process leads to the disease known as asbestosis.
Over a span of decades, constant movement can cause the sharp asbestos fibers to penetrate completely through the alveoli into the mesothelium surrounding the lungs (the pleura). The damage the fibers cause to the mesothelial cells disrupts normal cell reproduction and can cause malignant cells to form. When malignant cells begin reproducing, they eventually create a cancer tumor. The degree to which the tumor spreads within the mesothelium or spreads to other organs varies from individual to individual.
Causes of Pericardial and Peritoneal Mesothelioma
The relationship between breathing asbestos fibers and damage to the tissues in and surrounding the lungs is easy to understand. The process by which asbestos fibers are transported to the tissue surrounding the heart or the abdomen is much less clear.
It’s thought that some instances of these less common mesotheliomas are the result of asbestos fibers working their way from the lungs to other locations in the body, perhaps being carried in the bloodstream. Another theory is that swallowing the fibers may result in some of them penetrating the stomach or intestines.
Probability of Mesothelioma from Asbestos Exposure
Of the millions of people exposed to asbestos dust in the work place before asbestos became intensely regulated, only a small percentage have developed or are expected to develop mesothelioma. This is possibly a testament to the resilience of the body to resist disease processes. Nonetheless, the odds of developing the disease are much higher for people with heavy exposure than for the general population. The heavier and more prolonged the exposure, the higher the risk.
From 2,000 to 3,000 new cases are diagnosed each year, representing approximately 1 in every 50,000 adults.
You must log in to post a comment.