Visceral pleural thickening in asbestos exposure: the occurrence and implications of thickened interlobar fissures

Neoplastic and nonneoplastic conditions of serosal membrane origin: CT findings

Computed tomography (CT) is an important imaging modality for diagnosis and follow-up of neoplastic or nonneoplastic conditions of the serosal membrane. The characteristic CT findings of malignant pleural mesothelioma include unilateral pleural effusion, thickening of the mediastinal pleura, and circumferential and nodular pleural thickening of greater than 1 cm. Malignant peritoneal mesothelioma manifests as a large mass or diffuse peritoneal thickening without a definable mass and is difficult to differentiate from peritoneal carcinomatosis or tuberculosis. The imaging features of primary serous papillary carcinoma of the peritoneum resemble those of peritoneal carcinomatosis; however, the ovary is usually of normal size. The possibility of desmoplastic small round cell tumor should be considered in children or young adults with multiple peritoneal masses and no identifiable primary malignancy. The CT findings of secondary tumors include a variable amount of fluid in the serosal cavity, thickening of the serosal lining (irregular and nodular), and serosal implants. Nonneoplastic conditions manifest as focal or diffuse thickening of the serosal membrane, a variable amount of fluid in the serosal cavity, and a soft-tissue mass at CT. Although the CT findings of some of the conditions overlap, knowledge of the typical findings is helpful in narrowing the differential diagnosis.

Imaging of Pleural Disease

Imaging plays an important role in the diagnosis and subsequent management of patients with pleural disease. The presence of a pleural abnormality is usually suggested following a routine chest x-ray, with a number of imaging modalities available for further characterization. This article describes the radiographic and cross-sectional appearances of pleural diseases, which are commonly encountered in every day practice. The conditions covered include benign and malignant pleural thickening, pleural effusions, empyema and pneumothoraces. The relative merits of CT, MRI and PET in the assessment of these conditions and the role of image-guided intervention are discussed.

Radiology in pleural disease: State of the art

Diseases of the pleura and pleural space are common and present a significant contribution to the workload of the chest radiologist. The radiology department plays a crucial role in the imaging and management of pleural disease. This review aims to describe and illustrate the appearances of common pleural pathologies on various radiological modalities including plain film, ultrasound, CT, magnetic resonance imaging and positron emission tomography. The review will also address the state-of-the-art techniques used to image pleural disease and discuss image-guided intervention in the management of pleural disease.

Imaging of nonmalignant occupational lung disease

The radiologist plays an important partnership role in detecting presymptomatic disease in those at risk for occupational lung disease, contributing to the specificity of the diagnosis and recognizing sentinel events. Medicolegal roles for imaging include confirming the presence of a morphologic abnormality compatible with occupational lung disease, identifying other potential causes for disability, and determining the morphologic extent of disease. This article describes and illustrates the imaging appearance of a wide range of occupational lung diseases.

The suction mechanism as a factor in intrathoracic oedema, connective tissue or pleural effusion

In pathological conditions, the negative intrapleural pressures (Ppl) may increase unequally. At some sites they may remain increased. We maintain that at these sites the increased pressures may lead to the production of oedema in the adjacent pleural walls and in adjacent pre-existing connective tissue, which may remain as oedema or may become connective tissue. Occasionally the increased negative Ppl may contribute to the production of pleural effusion. We term all these processes the suction mechanism (SM). This mechanism affords an interpretation of a series of images observed in chest X-rays. According to this view, lung shrinkage, narrowing of the pulmonary vessels and impairment of the lung function are not caused by the diffuse pleural fibrosis, but result from damage to the lung parenchyma. We also interpret the apical cap, the blunting of the costophrenic sulci, the broadening of the mediastinum and the retrosternal stripe in terms of the SM.

Asbestos-related benign pleural disease

Benign pleural disease is the commonest manifestation of asbestos exposure encountered by radiologists. Benign pleural thickening can appear as circumscribed parietal pleural plaques or as more diffuse thickening of the visceral pleura. Benign-asbestos induced pleural effusions are a significant and under-recognized manifestation of asbestos exposure with important sequelae, such as diffuse pleural thickening which may be associated with functional impairment and for which compensation may be sought. This review concentrates on the strengths and weaknesses of chest radiography and computed tomography for the detection and characterization of benign asbestos-related pleural disease and the relevance of imaging abnormalities to compensation and functional impairment.Peacock, C. (2000). Clinical Radiology55, 422-432.

Radiographic small lung opacities and pleural abnormalities in relation to smoking, urbanization status, and occupational asbestos exposure in Finland

The role of smoking and an urban living environment in the etiology of radiographic pleural and pulmonary abnormalities was studied in a population sample that was representative of the Finnish adult population. A total of 7095 full-size chest radiographs were classified according to the International Labor Organization's 1980 classification of radiographs of pneumoconioses, with some modifications. The risk of bilateral pleural plaques was significantly higher among urban men (RR, 2.0) and women (RR, 3.8), even when adjusted for age and probability of occupational asbestos exposure and smoking. The risks of small lung opacities and abnormalities of the visceral pleura were not higher in urban areas. Risks of small lung opacities and thickening of the visceral pleura were positively associated with smoking, and the risk of small lung opacities was also higher among smokers than never-smokers in the population fraction with unlikely occupational asbestos exposure.

Prevalence of radiographic small lung opacities and pleural abnormalities in a representative adult population sample

The prevalence of radiographic widespread small lung opacities and pleural abnormalities in the general population was assessed as part of the Mini-Finland Health Survey, which was based on a representative sample of people aged 30 years or over. Full-size chest radiographs of 7,095 persons (89% of the sample) were classified. Two radiologists classified all the radiographs according to the ILO 1980 Classification of Radiographs of Pneumoconioses. Small lung opacities and pleural abnormalities were considerably more prevalent in the older age groups and in men. Small lung opacities on the radiographs and pleural abnormalities were associated with work in industrial occupations, particularly in men. There was a clear association between small lung opacities and pleural abnormalities. The sex differences may be related to occupational factors, particularly dust exposure. The elevated risk of pleural plaques in persons with small lung opacities on the radiographs may indicate a fiber effect.

Radiology of the pleural fissures

The pleural fissures, formed by a double layer of visceral pleura, represent extensions of the pleural space between lobes of the lungs. The fissures are frequently an anatomic barrier to the spread of inflammatory or neoplastic disease. Identification of the fissures is important for the accurate localization of lung parenchymal or pleural pathology. The plain radiographic and computed tomographic (CT) imaging of normal and variant fissural anatomy, as well as of some abnormalities that may affect the fissures will be reviewed and illustrated.

Asbestos-related chest diseases: plain radiographic findings

In summary, there are a wide range of pulmonary manifestations seen in asbestos-exposed individuals from pleural and parenchymal fibrosis to pleural and parenchymal malignancy. The chest roentgenogram has assumed an important role in the detection and surveillance of asbestos-related pleural and parenchymal changes.

Noninvasive detection of early asbestos-related disease of the thorax: algorithmic analysis of radiographic, nuclear, and serologic tests

Improved imaging techniques may assist in the diagnosis of early asbestosis, such as could occur from "asbestos in place." These include (1) increased visualization of visceral pleural thickening, (2) high-resolution computed tomography (HRCT), and (3) gallium scanning, combined with evidence of serum markers indicating inflammation-associated pulmonary collagen formation. Combining these imaging and serum test observations with a clinically useful algorithmic approach may permit the diagnosis of "early" asbestosis, which is not now possible from the individual test results or from an unweighted combination of such data.

High-resolution computed tomography of asbestos-related diseases

There is growing evidence that HRCT can detect both interstitial and pleural disease in advance of conventional clinical or radiographic studies. Limited HRCT scans are roughly competitive in time and cost with 4-view radiographic examinations. The use of limited HRCT for large-scale screening of asbestos-exposed individuals is controversial. Hopefully this will be resolved as we gain greater understanding of the specificity of HRCT and establish guidelines for standardizing technique and interpretation. At present, limited HRCT scans can supplement the chest radiographic evaluation of subjects in whom there is equivocal parenchymal or pleural disease, unexplained abnormalities on pulmonary function tests, or significant coexisting pleural disease that precludes evaluation of the underlying parenchyma. Interstitial abnormalities on HRCT may be reasonably ascribed to asbestos exposure when there is clear historical documentation of significant, remote dust exposure or concomitant evidence of typical bilateral asbestos-related pleural disease. A subpleural distribution of interstitial abnormality in nondependent lung is important to establish the diagnosis of interstitial fibrosis. Although both unilateral pleural and parenchymal fibroses have been reported, lesions should generally be present bilaterally. In individuals with combined asbestos-cigarette smoke exposure in whom symptoms or functional abnormalities are present, HRCT may play a central role in distinguishing emphysematous lung destruction from the peripheral interstitial changes of asbestosis. Finally, in individuals with significant pleural or parenchymal fibrosis, focal lung masses may not be visible on chest radiographs. In these individuals, CT protocols that sample all regions of the thorax are appropriate.

Radiological features of asbestos-related visceral pleural changes

The radiological manifestations of asbestos-related visceral pleural changes are described. Generally, visceral pleural reactions follow the mesothelial cells response to various injurious substances, including asbestos, and even saline. The changes are nonspecific. They may occur subsequent to pleural reactions associated with many conditions, which include tuberculosis, viral pleurisy, malignancy and lymphoma, lupus, or rheumatoid-induced effusions, cardiac failure, and pulmonary embolism, among other etiologies. The failure to absorb the fibrinous exudate on the visceral pleural surface can lead to the development of diffuse fibrosis of the serosal surface, interlobar pleural thickening, localized pleural filaments (strands), subpleural wedge, and lenticular-shaped masses, and could be the forerunner of lobular atelectasis (pseudotumor) formation. Some of the features are recognized on posteroanterior chest radiographs and the counterparts corroborated with the use of routine and high-resolution computed tomography studies.

Fissural thickening and exposure to asbestos: occurrence, determinants, and functional impact

The occurrence and determinants of thickened interlobar fissures were assessed in 147 insulators, in order to test the hypothesis that radiographic abnormalities in minor (FMN) and/or major (FMJ) interlobar fissures are associated with restrictive respiratory impairment, which may reflect early parenchymal lung fibrosis. According to the diagnostic criteria developed, definite interlobar thickening was found in 33 (FMN) and in 73 (FMJ) men, and was frequently associated with the presence of classical asbestos pleural disease, though not parenchymal abnormality. Multivariate analyses did not demonstrate any association between either FMN or FMJ and lung function. Such an association, however, was found in the case of the usual asbestos-related pleural change. These findings suggest that fissural thickening seen on chest radiography represents a component of asbestos pleural disease and not asbestosis.

Asbestos-related lesions of the pleura: parietal plaques compared to diffuse thickening studied with chest roentgenography, computed tomography, lung function, and gas exchange

Lung function tests, tests of working capacity with gas exchange, and computed tomography (CT) with density measurements with the patient supine and prone were performed in 23 males with asbestos-related bilateral pleural lesions. Two had pulmonary asbestosis grade 1/0 or more; all the others had normal lung parenchyma. On x-ray, the pleural lesions were divided into plaques involving only the parietal pleura There was a and diffuse pleural fibrosis of various degrees involving the visceral pleura. There was a good correlation between the findings at plain chest roentgenography and CT, but more lesions were seen on the CT scan. However, a few pleural plaques seen on conventional films were not observed at CT. Individuals with plaques had slightly lowered lung function compared to reference subjects. Bilateral diffuse pleural fibrosis was associated with a marked decrease in pulmonary function. The two patients with radiologically evident pulmonary asbestosis were found in this group. Decreased lung function was also observed in subjects with pleural fibrosis of only grade 1 (involving less than one fourth of the hemithorax) and a normal exercise capacity. The study shows the importance of differentiation between various asbestos-related pleural lesions.

Calcified plaque in the superior portion of the major fissure. An unusual manifestation of asbestos exposure

Parietal pleural plaque is a well-recognized sign of exposure to asbestos. Visceral pleural involvement is an uncommon manifestation, and calcified visceral pleural plaques are rare. Those reported have been in the minor fissure and inferior major fissure. We describe a unique calcified plaque in the superior major fissure.

Roentgenographic underestimation of early asbestosis by International Labor Organization classification. Analysis of data and probabilities

We analyzed the limitations of the International Labor Organization (ILO) classification of chest roentgenograms in predicting the presence of histologically determined early asbestosis. The ILO system is arbitrary, without histologic correlates, and does not consider the asbestos exposure history or clinical and laboratory information. We present data from the literature and our own work which demonstrate that the application of the ILO classification to an asbestos-exposed individual can result in a 10 to 20 percent probability of a "normal" roentgenographic interpretation in the presence of significant asbestosis at the histologic level, leading to an inappropriate conclusion regarding the presence of asbestosis. In view of the data and statistical analysis presented, we suggest that sole reliance upon the ILO classified chest roentgenogram for determination of the presence of early pulmonary asbestosis in individual cases is inappropriate.