The mesothelium is a membrane that covers and protects most of the internal organs of the body. It is composed of two layers of cells: One layer immediately surrounds the organ; the other forms a sac around it. The mesothelium produces a lubricating fluid that is released between these layers, allowing moving organs (such as the beating heart and the expanding and contracting lungs) to glide easily against adjacent structures.
Mesothelioma (cancer of the mesothelium) is a disease in which cells of the mesothelium become abnormal and divide without control or order. They can invade and damage nearby tissues and organs. Mesothelioma cancer is almost always caused by previous exposure to asbestos. Most people who develop mesothelioma cancer have worked on jobs where they inhaled asbestos particles, or have been exposed to asbestos dust and fibre in other ways, such as by washing the clothes of a family member who worked with asbestos, or by home renovation using asbestos cement products. Unlike lung cancer, there is no association between mesothelioma and smoking.
Mesotheliomas are uncommon cancers, although they are becoming more frequent. Currently, about 1800 people in the UK are diagnosed with mesothelioma cancer each year. Mesothelioma of the lining of the lungs (pleural mesothelioma) is much more common than mesothelioma in the peritoneum. For every person with peritoneal mesothelioma there will be about 12 people who have pleural mesothelioma.
1. Pleural mesothelioma cancer
The pleura has two layers: the inner (visceral) layer, which is next to the lung; and the outer (parietal) layer, which lines the chest wall. The two layers of the pleura are usually in contact and slide over each other as we breathe. The membranes produce fluid, which allows them to slide over each other easily.
When a mesothelioma cancer develops in the pleura (pleural mesothelioma), the delicate membranes thicken and may press inwards on the lung. Fluid may also collect between the two layers of the pleura: this is known as a pleural effusion.
2. Peritoneal mesothelioma cancer
The lining of the abdomen is known as the peritoneum. It also has two layers: the inner (visceral) layer, which is next to the abdominal organs; and the outer (parietal) layer, which lines the abdominal wall.
If the mesothelioma is in the peritoneum it is called peritoneal mesothelioma and causes thickening of the membranes surrounding the abdominal organs and a collection of fluid in the abdomen. The collection of fluid is called ascites and causes swelling of the abdomen.
