Pleural plaques are the most common condition associated with asbestos exposure; more than 80% of patients with pleural plaques have had a history of asbestos exposure. Pleural plaques develop 20 to 40 years after exposure to asbestos and may occur after low, intermittent exposure. After 20 years, uncalcified pleural plaques can be found in five to 15% of people who were exposed to asbestos at their workplace. Thirty years after the first exposure to asbestos, about a third to one half of people have calcified pleural plaques. A person with pleural plaques may show no other signs of asbestos exposure; however, pleural plaques are present in almost all patients with asbestosis, so the discovery of pleural plaques is a cause for concern.

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Pleural plaques are smooth, white, raised irregular areas of tissue formed from collagen bundles arranged in a basket-weave pattern. They almost always appear on the parietal pleura (the outer lining that surrounds the lung). The plaques may contain asbestos fibers and often become calcified as time goes by. They range from small to large, and if calcified can be more easily seen on a chest x-ray. 

The larger the plaque, the greater the chance that more asbestos fibers will be found in the patient's lungs, especially if the plaque is calcified. However, the absence of pleural plaques is not a guarantee that asbestos hasn't invaded the lungs; some people with no pleural plaques still have a high concentration of asbestos fibers in the lungs and pleura.

 

Information source www.asbestos.net