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Pleural plaque

Pleural plaques are the most common manifestation of asbestos related disease 1-2, and can be identified with a very high degree of specificity with CT. 

Epidemiology

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.

Clinical presentation

Pleural plaques are asymptomatic and incidentally found on radiography of the chest.

Pathology

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.

Radiographic features

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 disease1-2.

The plaques may be calcified however most (85-95%) are not 1-2.

Plain film

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 pleural1. Appearance has been likened to that of a holly leaf, which thickened rolled and nodular edges 4

CT

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.

Differential diagnosis

On plain film consider

See also

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