Chest ImagingPleural plaques
focal areas of
pleural thickening. They are composed of hyalinized fibrous tissue within which asbestos fibres can be seen with electron microscopy. They are caused by transpleural migration of asbestos fibres, particularly chrysotile, the least fibrogenic type of asbestos. The more fibrogenic and carcinogenic crocidolite is more likely to be trapped within the lungs. Plaques are seen 20 - 30 years after initial exposure to asbestos and the incidence increases with dose. They occur on the parietal layer of the
pleura, most frequently over the
diaphragm and posterolateral chest wall, especially along the line of the ribs. With increasing age, plaques may increase in size and
calcification is common.
Pleural plaques are the most frequent radiological manifestation of exposure to asbestos. On the frontal radiograph, plaques are seen as focal elevations of the pleura, detected most easily where they are in profile along the peripheral margins of the lungs. Plaques are usually multiple, with reasonable left-right symmetry and may enlarge over time and coalesce, producing sheets of thickened pleura. Characteristically, there is sparing of the apices, costophrenic angles and mediastinal contours.
Calcification is common; it is usually linear or lacelike and may produce a "holly leaf" appearance. CT is significantly more sensitive than chest radiography for the detection of plaques which are seen as focal areas of thickened pleura, usually adjacent to the inner surface of ribs or vertebral bodies (Fig.1, Fig.2). Plaques are often calcified and are usually slightly denser than adjacent intercostal muscles even when not calcified. Plaques may coalesce to form extensive sheet like lesions of diffuse pleural thickening.
Pleural plaques can usually be diagnosed with confidence on the basis of their characteristic radiographic and CT appearances. Occasionally biopsy is necessary to confirm the benign nature of the lesion when a plaque is unduly large or there is diffuse pleural thickening. Rarely, surgery with decortication is required if there is marked impairment of respiratory function. Pleural plaques are not necessarily associated with pulmonary parenchymal disease and pulmonary function is usually normal or only slightly reduced. There is no evidence that pleural plaques degenerate into malignant mesothelioma and plaques are not a significant marker of an increased risk of the development of malignant mesothelioma.
CF - HM
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CT image on mediastinal windows demonstrates multiple, bilateral, pleural plaques.
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Pleural plaques, Fig.1 | | Pleural plaques, Fig.2 | |