Pleural plaques, calcified

Involvement of the pleura, i.e. formation of pleural plaques (fibrotic masses on the pleura) may accompany asbestosis or occur independently, that is, as lesions with no obvious causal relationship (Whitwell, 1978). Pleural plaques only occasionally cause symptoms, as when they restrict the motion of the lung by thickening the membrane (pleura) around the lung or disrupting tissue viability by calcifying. 

Fig. 7.16. Thin-section computed tomography of a calcified pleural plaque (arrow) showing adjacent interstitial parenchymal lines...

Macroscopically, pleural plaques are discrete, raised, and irregularly shaped areas (Roberts 1971). They vary in size from a few millimeters to 10 cm. The thinner plaques are only slightly raised above the pleural surface, vdiile the thicker plaques are either smooth or show a fine or coarse nodularity. Most of the plaques have a leathery consistency, but as pleural plaques tend to calcify with time, more heavily calcified plaques are brittle and can be fractured (Roberts 1971). 

Fig. 8.3. Postero-anterior chest radiograph shows calcified pleural plaques appearing as bilateral dense opacities...

Fig. 8.4. Postero-anterior chest radiograph shows diaphragmatic calcified pleural plaques seen in profile (arrows), parallel to the X-ray beam...

Radiography, thus, has some limitations. A first limitation is that thin pleural plaques may be overlooked, especially if non-calcified and if viewed en face. Autopsy studies have shown that the plain radiograph demonstrates only a small percentage of pleural plaques detected by autopsy (Hourihane et al. 1966 Svenes et al. 1986). Oblique films, which bring off-midline, en face plaques into profile, have been suggested to increase the detection of plaques on radiographs. However, the routine use of oblique views has certain limitations. Normal peripheral densities, such as companion shadows and slips of the internal intercostal muscles, become more apparent and erroneously may be identified as pleural plaques (McLoud et al. 1985). Oblique films are. 

No study has investigated the diagnostic performance of CT in detecting pleural plaques by comparison with autopsy as the method of reference, but more plaques are detected using CT than radiography and, except for obviously calcified plaques, CT eliminates false-positive diagnoses of asbestos-related pleural disease caused by extrapleural fat (Friedman et al. 1988). CT is, thus, now widely recommended to detect pleural plaques in asbestos-exposed workers and plays an important role in medico-legal and compensation issues. 

Fig. 8.12. Computed tomography scan of the chest shows posterior calcified pleural plaque appearing as a discrete smooth line of calcium attenuation (arrows)...

Fig. 8.15a,b. Computed tomography scan of the chest photographed in mediastinal (a) and pulmonary (b) window settings shows a small amount of remnant fluid within the right pleural cavity in a patient who had a benign asbestos pleurisy. Note the presence of bilateral calcified pleural plaques, and parenchymal bands and rounded atelectasis in the right lower lobe... 

Fig. 8.20. Computed tomography scan of the chest shows a rounded atelectasis in the right lower lobe. Note the backward displacement of the major fissure as the evidence of lung volume loss in the surrounding lung. Other findings are the right calcified diffuse pleural thickening and the left calcified pleural plaque...

Sargent EN, Felton JS, Barnes LT (1981) Calcified interlobar pleural plaques visceral involvement due to asbestos. Radiology 140 634... 

Sargent EN, Boswell WD, Ralls PW, Markovitz A (1984) Sub-pleural fat pads in patients exposed to asbestos distinction from non-calcified pleural plaques. Radiology... 

Fig. 9.3a,b. Asbestos exposure in a 56-year-old man with malignant pleural mesothelioma, a Axial non-enhanced computed tomography scan shows concentric nodular pleural thickening. Bilateral calcified pleural plaques are seen (arrows). Note reduction in volmne of the affected hemithorax. b Axial enhanced computed tomography scan demonstrates that pleural nodules enhance following contrast administration... 

The pleura are connective tissue membranes composed of matrix, mesotheli-al cells, and fibroblasts. There are two types of pleural responses benign responses, such as thickening of the matrix, formation of plaques (which may calcify) or effusions, and fluid accumulation in the interpleural spaces between the visceral and parietal pleurae and neoplastic disease, or the malignancy known as mesothelioma. 

Solomon A, Sluis-Cremer GK, Thomas RG, Wright VMF (1984) Calcified plaques on mediastinal pleural reflections asso-... 

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