Asbestos-Related Pleural Disease
Asbestos is a family of naturally occurring silicates whose heat-resistant and structural properties made it useful for inclusion in construction and shipbuilding materials, automobile brakes, and some textiles. Chrysotile (a serpentine fiber), crocidolite, and amosite (amphibole, or straight fibers) are the 3 main types of asbestos that cause disease.
Asbestos can cause pleural disease other than mesothelioma, including benign asbestos effusion and benign pleural plaques. Such pleural disease causes effusion but few symptoms. Asbestos-related pleural disease can cause restrictive lung disease and impairment in diffusing capacity of carbon monoxide, even without the presence of interstitial fibrosis.
All pleural changes are diagnosed by chest x-ray or CT, though chest CT is more sensitive than chest x-ray for detecting pleural disorders. Treatment is rarely needed.
Benign asbestos pleural effusions (BAPE) are typically unilateral and occur 15 to 45 years after initial asbestos exposure. Unlike asbestosis, there is not a clear dose-response correlation to the amount of asbestos exposure. CT of the chest confirms the diagnosis in a patient with a history of asbestos exposure. Analysis of the pleural effusion demonstrates an exudative process and can be serous, serosanguinous, or overtly bloody. The presence of pleural plaques increases the likelihood of mesothelioma, thus diagnostic evaluation should be undertaken to rule out malignancy. BAPE can resolve overtime. BAPE alone does not predict risk of malignancy.
Discrete plaques, which occur in up to 60% of workers exposed to asbestos, typically affect the parietal pleura between the 5th and 9th ribs bilaterally and adjacent to the diaphragm. The apices and costophrenic angles tend to be spared. Plaque calcification is common and can lead to misdiagnosis of severe pulmonary disease when radiographically superimposed on lung fields. CT can distinguish pleural from parenchymal disease in this setting. Fat stripes may be mistaken for pleural plaques on chest x-ray. CT can distinguish pleural disease from fat.
Diffuse thickening affects visceral as well as parietal pleurae. It may be an extension of pulmonary fibrosis from parenchyma to the pleurae or a nonspecific reaction to pleural effusion. With or without calcification, pleural thickening can cause a restrictive defect.
Rounded atelectasis is a benign manifestation of pleural thickening in which invagination of pleura into the parenchyma can entrap lung tissue, causing atelectasis. On chest x-ray and CT, it typically appears as a curvilinear, scar-like mass, often in the lower lung zones, and can be confused with a pulmonary cancer.