Pleura mesothelioma is an aggressive form of cancer of the mesothelium membrane that lines the lungs and the walls of the chest cavity. Pleura mesothelioma usually develops unilaterally, which means it forms on one side of the chest or the other. The cancer begins as a series of small white nodules, which spread on the surface of the pleural membrane. The small nodules will gradually grow together and thicken to form a tumor that spreads and invades surrounding tissue. The tumor surrounds the lungs and extends into the pleura membrane and the muscle known as a diaphragm. In the process it inwardly compresses the lung and outwardly invades the chest wall and ribs. As the disease progresses an effusion from the build up of fluids stops the lungs from fully expanding. This causes a progressive shortness of breath while chest pains result from the invasion of the chest wall. Acute symptoms of the disease then become evident.

Pleural effusion will show on an x-ray for most patients, but some patients show little or no fluid build up. In the early stages of pleural mesothelioma, the fluid is free flowing, similar to that seen for other benign situations or that seen in the case of congestive heart failure. An initial diagnosis that includes an x-ray may indicate either of these problems. However, as the disease progresses, the effusion becomes loculated, which means it is contained in the pleural space and the fluid does not move. A CAT scan will provide a more definitive picture of the effusion as well as pleural masses and lymph nodes. A MRI will provide an even more definitive picture. A MRI will indicate the level of any invasion of the chest wall and the extent to which the disease has invaded the diaphragm. A positron emission tomography (PET) will stage the disease by indicating whether the disease has extended to the other lung or to other areas of the body.

 A fluid analysis or biopsy may be used to diagnose and confirm pleural mesothelioma, but such methods have traditionally proved to make a definitive diagnosis for only a small number of patients. A video assisted thoracoscopy (VATS) is a more reliable procedure, providing a definitive diagnosis in greater than 95% of patients who have been given the procedure. A VATS procedure includes a pleural biopsy, drainage of fluid in the pleural membrane and the extraction of tissue samples. The video ensures that adequate tissue samples are extracted to make a definitive diagnosis. Pleural mesothelioma is the only form of mesothelioma for which a staging system exits to identify how far the disease has progressed. Staging is based on the tumor, lymph nodes and metastasis (TNM) staging system, which combines information about tumors, lymph nodes and metastasis into stage grouping and assigns a number to the groupings. The staging for pleural mesothelioma is as follows: 

A surgical procedure may be used to stop fluid from building up and also to relieve patients of some of the symptoms of pleural mesothelioma. This procedure is known as pleurodesis. The procedure involves sealing the space between pleura membrane with either a sterile talc or antibiotic. These substances are expected to irritate the pleura membrane and cause them to stick together, and thus, prevent the build up of fluids.