What is Mesothelioma?
Malignant mesothelioma is a cancer which affects the thin membranes which line the chest and lung (called pleural mesothelioma), the abdomen (called peritoneal mesothelioma) or the sack like space around the heart (pericardium mesothelioma).
The mesothelium is the cell tissue that forms the lining of the chest and abdomen. Mesothelioma is the cancer that is found in these linings.
Types of Mesothelioma
This is a cancer found in the linings of the chest and lung. It is by far the most common mesothelioma accounting for approximately 90 to 95% of mesotheliomas, in the UK.
The pleural lining has two layers. There is an inner (called visceral) layer which lines the lung and an outer layer (called the parietal) which lines the chest wall. The pleura (these two linings) produce fluid to lubricate the space between the two layers allowing the layers to slide comfortably over each other during breathing.
Pleural mesothelioma causes the pleura to thicken. This may make it press on the lung or attach itself to the chest wall. Fluid, sometimes as much as several litres often collects between the two layers and causes breathlessness. This is known as a pleural effusion.
The peritoneal (the abdomen) also has two layers. The inner (visceral) layer is next to the abdominal organs and the outer (parietal) layer lines the abdominal wall. Mesothelioma causes the peritoneum to thin and for fluid to collect in the abdomen. This fluid is called ascites and causes abdomen swelling.
Peritoneal mesothelioma is much less common than pleural mesothelioma in the United Kingdom, accounting for only 5 to 10% of mesotheliomas.
There is uncertainty as to how asbestos exposure leads to the development of peritoneal mesothelioma. One school of thought is that the asbestos fibres are ingested, and that the asbestos fibres make their way from digestive organs into the peritoneal membrane. An alternative possibility is that the asbestos fibres are inhaled and that they travel to the peritoneal membrane through the lymphatic system. What is clear is that over time the asbestos fibres irritate the mesothelioma cells leading to changes in the cells and ultimately the cancer.
Very occasional mesothelioma tumours arise in other sites such as the pericardium (the sack like space around the heart); and also very occasionally the testes.