The pleura is a membrane that lines the chest cavity wall, and that also provides an outer protective covering for the lungs. That portion of the pleura that covers the chest wall is called the parietal pleura; the outer lung lining is called the visceral pleura. Under normal circumstances there is a thin coat of fluid between the two facing surfaces that allows the lungs to slide easily against the chest wall membrane when the lungs are inhaling and exhaling. The pleura is a portion of a larger membrane called the mesothelium, which surrounds many organs in the body and lines the wall of the abdominal cavity as well. Malignant mesothelioma develops in various areas of the mesothelium – hence the name for the disease.
Pleural Thickening and Mesothelioma
Pleural thickening is one of the symptoms of pleural mesothelioma, by far the most common form of the disease. The tissue surrounding the lungs, and/or lining the chest wall develops inflammation thickens as abnormal cells are generated by the presence of asbestos fibers. Pleural thickening is often accompanied by pleural effusion when the active disease is malignant mesothelioma. Effusion is the generation of excess fluid in the area; the combination of the fluid and thickened membranes can put substantial pressure on the lungs. Excess fluid can cause inflammation of the pleura and can be a direct cause of pleural thickening.
Pleural thickening can also occur with benign mesothelioma, which is the generation of diffuse benign tumors on the pleura. The body generates excessive connective tissue in an attempt to rid itself of the asbestos fibers. This condition is called pleural fibrosis; it can lead not only to thickening but also to a reduction in the flexibility of the pleura as well. Sarcoidosis, which is a chronic inflammation of the pleura unrelated to mesothelioma, can cause pleural thickening as well.
With benign mesothelioma there may not be the presence of excess fluid, and in some cases of malignant mesothelioma there may an absence of fluid generation as well. Pleural thickening in these circumstances can lead to the chest wall and the lungs rubbing against each other during the breathing process, a condition that can be extremely painful for the patient.
Another condition associated with the presence of asbestos fibers in the pleura is pleural plaques. These are small growths that undergo calcification and can lead to thickening in some areas of the pleural surface. Diffuse pleural thickening occurs when there is widespread fibrosis; when pleural effusion causes a general inflammation, and when diffuse mesothelioma tumors begin to develop.
Symptoms of Pleural Thickening
The first symptoms of pleural thickening in mesothelioma patients are mild shortness of breath and the accompanying loss of stamina. As the disease progresses difficulty in breathing generally increases and this may be due to a number of causes, causing any or all of the following symptoms in patients with pleural thickening:
- Chest pain
- Shortness of breath
- Decreased physical ability
- Sound of friction rub
- Tightness in the chest
Pleural effusion can cause shortness of breath and certainly the presence of tumors will impact respiratory ability, but the existence of diffuse pleural thickening with fibrosis characteristics will cause a substantial reduction in breathing capacity. The accompanying chest pain may be due to pressure on the lungs from the thickened pleura, or there may be a friction rub between the chest wall and the lungs, or both.
Diagnosis of Pleural Thickening
Often the medical examination of pleural thickening will also be a process of trying to determine whether the cause is a benign disturbance of the chest cavity or a malignant disease such as mesothelioma. A CT scan is used to some effect, although the thickening must have reached a certain dimension in order to be distinguishable. The use of positron emission tomography (PET) utilizes a different type of imaging and can provide a more accurate analysis of the presence and to a degree, the cause of pleural thickening.
The imaging procedures can establish the existence of pleural thickening but establishing the cause will require a tissue or fluid sample. These may be retrieved by thoracentesis, inspection through a thorascopy procedure, or a biopsy retrieved through a minor surgical procedure.
Pleural Thickening Treatment
Normally, physicians will treat pleural thickening in mesothelioma patients by attempting to relieve the pressure placed upon the lungs. Without treatment, the pleural thickening in mesothelioma can lead to extreme discomfort and substantial respiratory difficulty. In extreme cases, physicians may combat the pleural thickening in mesothelioma patients through a process called pleurectomy, which is removal of the pleura. Usually this procedure is utilized only when there is an advanced case of diffuse pleural thickening with fibrosis that has hardened the pleura to the point that it is restricting the lungs. In the case of mesothelioma a pleurectomy can be part of the surgical procedure to remove malignant tissue.
Treatment of pleural thickening in mesothelioma patients may also involve reducing pleural effusion that may be contributing to the thickening. This procedure is called thoracentesis and involves removal of the fluid with a long needle inserted into the chest cavity. For cases of pleural thickening related to benign diseases there are not a lot of treatment protocols designed to reduce the inflammation.
- Clinical consequences of asbestos-related diffuse pleural thickening: Journal of Occupational Medicine and Toxicology, Miles et al, Sept. 2008
- PET for the Evaluation of Pleural Thickening Observed on CT, Kramer et al, The Journal of Nuclear Medicine, Vol. 45 2004