Pleural plaques are the most common manifestation of asbestos related disease, and can be identified with a very high degree of specificity with CT.
Pleural plaques are strongly associated with inhalational exposure to asbestos. There is an extremely long latency (typically 20 to 30 years) after the onset of exposure 1. As asbestos is primarily used in construction and machinery environments, asbestos related diseases in general, including pleural plaques, are primarily seen in men.
Pleural plaques are asymptomatic and incidentally found on radiography of the chest.
Fibres are thought to reach the pleural space via the lymphatic system. Macroscopically pleural plaques appear as grey-white regions of pleural thickening, often thickest at the margins, giving rise to the holly leaf appearance (aside from the colour of course).
Microscopically, they are composed of dense hyalinised collagen and are relatively acellular. The collagen is usually arranged in a loose 'basket-weave' pattern. Although asbestos fibres are sometimes seen, asbestos bodies are not a feature 1,3.
Pleural plaques typically arise from the parietal pleura, most frequently from the lower portions of the chest, sparing the apices and costophrenic angles. They are also frequently found arising from the mediastinal pleura. Visceral pleura may also be affected infrequently. When such visceral plaques are present, they are typically associated with underlying parenchymal abnormalities and extensive pleural disease 1-2.
The plaques may be calcified, however, most (85-95%) are not 1-2.
Pleural plaques exhibit the so called "incomplete border sign" on chest radiograph. The inner margin is often well defined because it is tangential to the x-ray beam and the adjacent lung is a good contrast medium. The tapering outer margin is indistinct as it is en face to the x-ray beam and the chest wall provide less tissue contrast. Calcified plaques is more obvious than non-calcified plaques to be identified. Locations most commonly encountered include posterolateral, mediastinal and diaphragmatic pleural 1. Appearance has been likened to that of a holly leaf, which thickened rolled and nodular edges 4.
CT is the modality of choice for assessment of pleural plaques, able to identify plaques anywhere in the chest, whether calcified or not. Sensitivity and specificity are both very high (95-100%) 1. With coronal and sagittal reconstructions, the diaphragmatic domes and apices are also well imaged.
Visceral pleural plaques have a predilection for the interlobar fissures and are usually associated with adjacent parenchymal abnormalities. In some instances, short linear regions of fibrosis are seen extending radially away from the the plaque (so-called hairy plaques) 1.
Treatment and prognosis
Pleural plaques are benign are require no treatment of follow-up.
On plain film consider:
- diffuse asbestos related pleural thickening: diffuse pleural thickening
- extrapleural fat
- rib fracture
- pleural tumours
- pleural pseudoplaques
- 1. Roach HD, Davies GJ, Attanoos R et-al. Asbestos: when the dust settles an imaging review of asbestos-related disease. Radiographics. 2002;22 Spec No : S167-84. Radiographics (link) - Pubmed citation
- 2. Kim KI, Kim CW, Lee MK et-al. Imaging of occupational lung disease. Radiographics. 21 (6): 1371-91. Radiographics (full text) - Pubmed citation
- 3. Roggli VL, Oury TD, Sporn TA. Pathology of asbestos-associated diseases. Springer Verlag. (2004) ISBN:0387200908. Read it at Google Books - Find it at Amazon
- 4. Cugell DW, Kamp DW. Asbestos and the pleura: a review. Chest. 2004;125 (3): 1103-17. doi:10.1378/chest.125.3.1103 - Pubmed citation
- 5. Hansell DM, Bankier AA, Macmahon H et-al. Fleischner Society: glossary of terms for thoracic imaging. Radiology. 2008;246 (3): 697-722. Radiology (full text) - doi:10.1148/radiol.2462070712 - Pubmed citation