Asbestos induced diffuse pleural fibrosis: pathology and mineralogy

Yellow Nail Syndrome with Bilateral Pleural Plaques and Diffuse Pleural Thickening: A Mimic of Asbestos Related Disease

Yellow nail syndrome is a rare acquired condition of unknown aetiology associated with distinct nail discolouration/xanthonychia, pulmonary manifestations, and lymphoedema. Pleural plaques and diffuse pleural thickening are typically, although not exclusively, recognised as markers of prior commercial asbestos exposure. The presence of such biomarkers may assist an asbestos personal injury evaluation. A postmortem examination performed on a 72-year-old man with known long-standing yellow nail syndrome identified pleural plaques and diffuse pleural thickening. An evaluation of the occupational history identified no known asbestos exposure. Electron microscopic mineral fibre analysis detected no asbestos fibres. To the best of our knowledge, this is the only case of yellow nail syndrome in which these benign pleural changes are reported ex asbestos. Alternate causes for such pleural pathology were absent. There is merit in physicians and pathologists having an awareness of these new manifestations when considering claimed asbestos related changes during life and at postmortem.

Non-neoplastic and neoplastic pleural endpoints following fiber exposure

Exposure to asbestos fibers is associated with non-neoplastic pleural diseases including plaques, fibrosis, and benign effusions, as well as with diffuse malignant pleural mesothelioma. Translocation and retention of fibers are fundamental processes in understanding the interactions between the dose and dimensions of fibers retained at this anatomic site and the subsequent pathological reactions. The initial interaction of fibers with target cells in the pleura has been studied in cellular models in vitro and in experimental studies in vivo. The proposed biological mechanisms responsible for non-neoplastic and neoplastic pleural diseases and the physical and chemical properties of asbestos fibers relevant to these mechanisms are critically reviewed. Understanding mechanisms of asbestos fiber toxicity may help us anticipate the problems from future exposures both to asbestos and to novel fibrous materials such as nanotubes. Gaps in our understanding have been outlined as guides for future research.

Reduction of CXC chemokine receptor 3 in an in vitro model of continuous exposure to asbestos in a human T-cell line, MT-2

Because patients with silicosis who are chronically exposed to silica particles develop not only pulmonary fibrosis, but also complications involving autoimmune diseases such as rheumatoid arthritis and systemic sclerosis, exposure to asbestos may affect the human immune system. This immunologic effect may impair antitumor immune function because cancer complications such as lung cancer and malignant mesothelioma are found in patients exposed to asbestos. To elucidate the antitumor immune status caused by CD4(+) T cells exposed to asbestos, an in vitro T-cell model of long-term and low-level exposure to chrysotile asbestos was established from a human adult T-cell leukemia virus-1-immortalized human polyclonal T cell line, MT-2, and the resulting six sublines showed resistance to asbestos-induced apoptosis after more than 8 months of continuous exposure. The results of DNA microarray analysis showed that the expression of 139 genes was altered by long-term and low-level exposure to asbestos, and the profile was almost similar among the six sublines when compared with the original MT-2 cells that had never been exposed to asbestos. Pathway and network analysis indicated a down-regulation of IFN-γ signaling and expression of CXC chemokine receptor 3 (CXCR3) in the sublines, whereas ELISA and flow cytometry analysis demonstrated a reduction in Th1-related IFN-γ production and cell-surface CXCR3 expression. These findings suggest that chronic exposure to asbestos may reduce antitumor immune status in CD4(+) T cells, and that an in vitro T-cell model may be useful in identifying molecules related to the impairment of antitumor immune function.

Pseudoneoplastic lesions: general considerations

Pseudoneoplastic lesions ("pseudotumors") can be seen in virtually all anatomic locations. Some organ sites, such as the lungs and skin, are overrepresented for unknown reasons, and the histologic images seen in pseudoneoplastic lesions are partially overlapping in disparate locations. More than occasionally, the degree of histologic likeness to true neoplasms-often malignant ones-is striking. This overview outlines the spectrum of pseudoneoplastic lesions and divides them into etiologic categories, including reparative, developmental, functional (usually endocrine), iatrogenic, infectious, and idiopathic. Side-by-side pictorial comparisons of selected pseudoneoplastic lesions and their neoplastic mimics are included.

Asbestos-Related Lung Disease

Asbestos is a high-profile health hazard. This article examines the assessment asbestos-related malignant mesothelioma and lung cancer. The risk of developing these diseases increases in proportion to the cumulative dose. As persons with heavy occupational asbestos exposures are diminishing, the observed latent period for asbestos-related disease extends making the assessment of an individual's cumulative dose is now more problematic.

Pleural effects of indium phosphide in B6C3F1 mice: nonfibrous particulate induced pleural fibrosis

The mechanism(s) by which chronic inhalation of indium phosphide (InP) particles causes pleural fibrosis is not known. Few studies of InP pleural toxicity have been conducted because of the challenges in conducting particulate inhalation exposures, and because the pleural lesions developed slowly over the 2-year inhalation study. The authors investigated whether InP (1 mg/kg) administered by a single oropharyngeal aspiration would cause pleural fibrosis in male B6C3F1 mice. By 28 days after treatment, protein and lactate dehydrogenase (LDH) were significantly increased in bronchoalveolar lavage fluid (BALF), but were unchanged in pleural lavage fluid (PLF). A pronounced pleural effusion characterized by significant increases in cytokines and a 3.7-fold increase in cell number was detected 28 days after InP treatment. Aspiration of soluble InCl(3) caused a similar delayed pleural effusion; however, other soluble metals, insoluble particles, and fibers did not. The effusion caused by InP was accompanied by areas of pleural thickening and inflammation at day 28, and by pleural fibrosis at day 98. Aspiration of InP produced pleural fibrosis that was histologically similar to lesions caused by chronic inhalation exposure, and in a shorter time period. This oropharyngeal aspiration model was used to provide an initial characterization of the progression of pleural lesions caused by InP.

Pathology of the Pleura

The pleura and lung are intimately associated and share many pathologic conditions. Nevertheless, they represent two separate organs of different embryonic derivation and with different yet often symbiotic functions. In this article, the authors explore the pathologic manifestations of the many conditions that primarily or secondarily affect the pleura.

Primary pleural epithelioid haemangioendothelioma with metastases to the skin. A case report and literature review

Epithelioid haemangioendothelioma (EHE) is a rare vascular tumour of intermediate behaviour. It can arise from various sites including the liver, spleen, pleura, or lung. Cutaneous EHE can be primary or secondary. This report describes the case of a 51 year old man who presented with a history of dry cough, shortness of breath, and pleural effusion, and who developed two cutaneous nodules in the anterior abdominal wall a few weeks later. He had a previous history of asbestos exposure. Computed tomography scan showed a left sided pleural effusion and nodular pleural mass. Histology of both the pleural and cutaneous lesions was compatible with EHE. Electron microscopic examination demonstrated the presence of Weibel-Palade bodies. The patient underwent elliptical excision of the metastatic cutaneous nodules after decortication of the primary pleural tumour and adjuvant treatment. A few reports have described metastasis of intrathoracic EHE to the skin. Despite treatment with interferon, the patient developed more cutaneous lesions two years after the initial diagnosis. Even though the tumour has the classic light histological and ultrastructural features of EHE, it behaved in an aggressive manner.

Causes and management of pleural fibrosis

The development of pleural fibrosis follows severe pleural space inflammation which is typically associated with an exudative pleural effusion. The response of the mesothelial cell to injury and its ability, along with the basement membrane, to maintain its integrity, is vital in determining whether there is normal healing or pleural fibrosis. The formation of a fibrinous intrapleural matrix is critical to the development of pleural fibrosis. This matrix is the result of disordered fibrin turnover, whereby fibrin formation is up-regulated and fibrin dissolution is down-regulated. Cytokines, such as TGF-beta and TNF-alpha, facilitate the fibrin matrix formation. A complete understanding of the pathogenesis of pleural fibrosis and why abnormal pleural space remodeling occurs in some and not in others, remains unknown. Clinically significant pleural fibrosis requires involvement of the visceral pleura. Isolated parietal pleural fibrosis, as with asbestos pleural plaques, does not cause restriction or respiratory impairment. The causes of visceral pleural fibrosis include asbestos-associated diffuse pleural thickening, coronary bypass graft surgery, pleural infection (including tuberculous pleurisy), drug-induced pleuritis, rheumatoid pleurisy, uraemic pleurisy, and haemothorax. Systemic and intrapleural corticosteroids administered during the initial presentation of rheumatoid pleurisy in small series may decrease the incidence of pleural fibrosis. Several randomised control trials using corticosteroids in tuberculous pleurisy have not shown efficacy in reducing residual pleural fibrosis. Decortication is effective in treating symptomatic patients regardless of the cause of pleural fibrosis as long as chronicity has been documented and significant underlying parenchymal disease has been excluded.

Asbestos: when the dust settles an imaging review of asbestos-related disease

Asbestos-related neoplastic and nonneoplastic diseases of the lungs and pleura range from pleural effusion and pleural plaques to lung cancer and malignant mesothelioma. Pleural effusions are typically hemorrhagic exudates of mixed cellularity but do not typically contain asbestos bodies. The classic distribution of pleural plaques seen on chest radiographs is the posterolateral chest wall between the seventh and tenth ribs, lateral chest wall between the sixth and ninth ribs, the dome of the diaphragm, and the mediastinal pleura. Computed tomographic (CT) findings support this distribution but also show anterior and paravertebral plaques not well shown at chest radiography. Imaging features of diffuse pleural thickening include a continuous sheet, often involving the costophrenic angles and apices, that rarely calcifies. The typical CT features of round atelectasis are of a round or oval mass that abuts the pleura, a "comet tail" of bronchovascular structures going into the mass, and thickening of the adjacent pleura. Features of asbestosis on chest radiographs include ground-glass opacification, small nodular opacities, "shaggy" cardiac silhouette, and ill-defined diaphragmatic contours. CT, however, is more sensitive in their detection. Chest radiography in patients with malignant mesothelioma may show an effusion, pleural thickening, and as the tumor progresses, a more lobulated outline. CT can help identify the disease in its early stages. Asbestos-related cancers can occur anywhere in the lungs. Recognition of the clinical, radiologic, and pathologic features of these diseases will be important for some years to come.

Malignant vascular tumours of the pleura in "asbestos" workers and endothelial differentiation in malignant mesothelioma

BACKGROUND

Three cases of diffuse malignant vascular tumours of the pleura are described which mimicked malignant mesothelioma clinically and pathologically (so called "pseudomesothelioma"). All had occupational histories of exposure to asbestos. The relationship of these tumours to mesothelioma and asbestos exposure is discussed.

METHODS

To examine the histogenetic relationship between mesothelioma and these three tumours an immunohistochemical analysis of vascular marker (CD31, CD34, and Von Willebrand factor) expression was undertaken in 92 cases of pleural mesothelioma, in addition to these three tumours. Electron microscopic fibre analysis of lung tissue was performed on each of the three cases to assess asbestos fibre content.

RESULTS

Diffuse pleural epithelioid haemangioendotheliomas may closely resemble malignant mesothelioma clinically and pathologically but, of the 92 pleural mesotheliomas tested, none showed expression of CD31, CD34, and Von Willebrand factor. Although all three cases had claimed exposure to asbestos, ferruginous bodies typical of asbestos were only seen by light microscopy in case 2, and only in this subject was the asbestos fibre content raised in comparison with the range seen in a non-exposed background population. The latent period in the pleural epithelioid haemangioendotheliomas ranged from 18 to 60 years.

CONCLUSIONS

Endothelial differentiation does not appear to occur in mesothelioma and therefore should be clearly separated from it. No definite association between pleural epithelioid haemangioendothelioma and exposure to asbestos can be made from this small series but further investigation is warranted.

Anti-mesothelial markers in sarcomatoid mesothelioma and other spindle cell neoplasms

AIMS

To undertake a comparative evaluation of three antimesothelial markers (thrombomodulin, cytokeratin 5/6 and calretinin) with broad spectrum cytokeratin (AE1/AE3) in differentiating between sarcomatoid mesothelioma and a spectrum of spindle cell neoplasms.

METHODS AND RESULTS

Thirty-one malignant sarcomatoid mesotheliomas were studied. Calretinin expression was focally identified in 12 (39%) tumours and thrombomodulin and cytokeratin 5/6 immunoreactivity was seen in nine (29%) cases. In comparison there was strong diffuse cytoplasmic reactivity with the broad spectrum cytokeratin (AE1/AE3) in 24 of 31 (77%) tumours. Thirty mixed spindle cells neoplasms were studied. No calretinin expression was identified in any case. Thrombomodulin immunoreactivity was identified in four (16%) cases (two angiosarcomas, two high-grade sarcomas, not otherwise specified). Cytokeratin 5/6 expression was seen in one high-grade pulmonary sarcoma originally termed malignant fibrous histiocytoma. None of the antimesothelial markers was expressed in the four spindle cell carcinomas studied. In contrast, broad spectrum cytokeratin was diffusely expressed in all four spindle cell carcinomas (three pulmonary, one renal), both synovial sarcomas, both malignant mixed Müllerian tumours, one of three pulmonary leiomyosarcomas and two of nine sarcomas, not otherwise specified.

CONCLUSIONS

Immunohistochemistry has a more limited role in the diagnosis and distinction of sarcomatoid mesothelioma from other spindle cell neoplasms. The combination of a broad spectrum cytokeratin with calretinin combines both high sensitivity (77% for AE1/AE3) with high specificity (100% for calretinin) for sarcomatoid mesothelioma and can be diagnostically useful. The mesothelial markers, thrombomodulin and cytokeratin 5/6, are not useful alone in the diagnosis of sarcomatoid mesothelioma as each shows insufficient antibody sensitivity, although together they complement calretinin.

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.

Asbestos upregulates expression of the urokinase-type plasminogen activator receptor on mesothelial cells

Inhalation of asbestos is associated with pathologic changes in the pleural space, including pleural thickening, pleural plaques, and mesothelioma. These processes are characterized by altered local proteolysis, cellular proliferation, and cell migration, suggesting that the urokinase-type plasminogen activator receptor (uPAR) could be involved in the pathogenesis of asbestos-induced pleural disease. We hypothesized that mesothelial cell uPAR expression is induced by exposure to asbestos. To test this hypothesis, we used complementary techniques in rabbit and human mesothelial cells to determine whether uPAR expression is altered by exposure to asbestos. uPAR expression was induced by chrysotile and crocidolite asbestos, but not by wollastonite, as indicated by binding of radiolabeled urokinase-type plasminogen activator (uPA) to rabbit or human mesothelial cells. uPA was not induced by fiber exposure. Exposure to exogenous uPA increased uPA activity of cells exposed to wollastonite but not asbestos-treated MeT5A cells. uPAR expression increased further when asbestos was preincubated with vitronectin (VN) or serum. Increases in uPAR expression were confirmed by binding of uPA to uPAR in cell membrane preparations and immunofluorescent staining of uPAR at the cell surface, and were associated with increases in steady-state uPAR messenger RNA. Mesothelial cell uPAR expression was also induced by media from monocytes cultured with asbestos incubated with VN and serum. By antibody neutralization, the latter effect appeared to be in part mediated by transforming growth factor-beta. We found that asbestos increases uPAR at the surface of rabbit and human mesothelial cells, suggesting that altered expression of this receptor could be involved in asbestos-induced remodeling of the pleural mesothelium.

Asbestos-induced pleural disease

Asbestos-induced pleural disease has become the most common manifestation of asbestos exposure. Asbestos has an unusual affinity for the pleural space and leads to plaques, benign effusions, fibrosis, and malignant mesothelioma. The explanation for its affinity for the pleura may lie in part with new evidence showing that asbestos fibers can accumulate in certain regions of the parietal pleura at higher concentrations than in the lung. With the control of industrial exposures to asbestos, the incidence of this disease should decrease, with the incidence of mesothelioma peaking in the years 2000 to 2020. Nonetheless, the toxic features of asbestos including shape, chemical composition, and surface characteristics should be understood to avoid toxicity in fibers used to replace asbestos and to know the risks of low level exposures from asbestos currently in our environment.

Analysis and interpretation of inorganic mineral particles in "lung" tissues

Mineral analysis of tissue specimens has provided very useful information in pathological conditions associated with occupational exposures to mineral particles, particularly when combined with epidemiological information. Most of the data have been related to exposures to fibrous particles such as asbestos. More investigations of this nature are required in diseases associated with exposure to non-fibrous particles. In the future it is likely that these types of investigation will be extended into the effects of pollutants.

Asbestos-induced visceral pleural fibrosis reduces pulmonary compliance

To determine the nature of respiratory functional impairment caused by asbestos-induced visceral pleural fibrosis (VPF) and to discover which pulmonary physiological variable best reveals it, we examined 59 asbestos-exposed construction workers having asbestos-related changes on chest radiographs. Computed tomography scans of the thorax were also performed. Visceral pleural fibrosis was diagnosed in 29 subjects: seven had only VPF, 17 had VPF and pleural plaques, and five had VPF, plaques, and asbestosis. In subjects without VPF, 23 had plaques, six had plaques and asbestosis, and one had only minor fibrotic parenchymal changes insufficient for a diagnosis of asbestosis. Flow-volume spirometry, body plethysmography, static and dynamic compliance, and pulmonary diffusing capacity for carbon monoxide were measured. The subjects with VPF had significantly lower static (p = 0.005) and dynamic (p = 0.007) compliance values than those without. Other respiratory function variables failed to show any significant differences. We conclude that the measurement of static and dynamic compliance is a useful method in assessing pulmonary function impairment caused by visceral pleural fibrosis.

Asbestos-related rounded atelectasis. Radiologic and mineralogic data in 23 cases

A retrospective study was conducted in 23 subjects with previous occupational exposure to asbestos and exhibiting rounded atelectasis (RA) on high-resolution computed tomography scan (HRCT scan) to evaluate the retention of asbestos bodies (ABs) using light microscopy in the bronchoalveolar lavage (BAL) fluid or lung parenchyma in such patients. A total of 31 RAs were identified, usually located in the lower (25 RAs) and posterior (23 RAs) parts of the lung. Pleural thickening in contact with the RA was observed in 27 RAs and parenchymal bands were detected in 15 cases. Twelve of the 20 patients who underwent BAL or surgery exhibited significant retention of ABs in BAL fluid or lung tissue. Moreover, a significant retention of ABs was observed in five of nine patients with a history of asbestos exposure but no diffuse pleural thickening on chest radiograph or interstitial opacities on HRCT scan. Patients with RAs and coexisting diffuse pleural thickening and/or interstitial fibrosis should be considered at a higher risk for lung cancer in comparison to patients with isolated circumscribed pleural plaques based on increased AB counts. By contrast, the excess risk of lung cancer is more questionable in patients with only RAs and circumscribed pleural plaques as they may have AB counts either above or below that associated with pleural plaques alone. This emphasizes the need for further follow-up studies to define criteria indicating the need for thoracotomy in these subjects.

Radiological changes in asbestos cement workers

OBJECTIVE

To explore associations between exposure to asbestos cement dust and radiographic findings in lung parenchyma and pleura.

METHODS

Radiographs from 174 blue collar workers and 29 white collar workers from an asbestos cement plant formed one part of the study. Progression of small opacities was further studied in those 124 blue collar workers, for whom two radiographs taken after the end of employment were available. The median readings from five readers who used the full ILO 1980 classification were used. As exposure indices, time since start of employment, duration of employment, cumulative exposure, and average intensity of asbestos exposure were used. The influence of age and smoking was also considered in multiple logistic regression analyses.

RESULTS

Small opacities (profusion > or = 1/0) were closely correlated with time related exposure variables, and showed weaker association with intensity based exposure variables. The odds ratio (OR) for small opacities was equal to 2.8 (90% CI 1.2, 6.7) in the > 30 f(fibre)-y/ml group, compared with those in the 0-10 f-y/ml group. Progression of at least two minor ILO categories after the end of employment was seen in 20%. Also, pleural thickening was closely related to time. By contrast, costophrenic angle obliterations were not associated with the time related variables, but closely associated with the intensity of asbestos exposure, and tended to occur during employment. The OR was 4.5 (90% CI 1.3, 15) in the > 2 f/ml group, compared with those in the 0-1 f/ml group.

CONCLUSIONS

In these workers, exposed mainly to chrysotile but also to small amounts of amphibole, the risk of radiographically visible parenchymal abnormality was substantially increased and strongly dependent on time related exposure variables. Progression was found long after the end of exposure. The findings on costophrenic angle obliterations, supposed to be sequelae of benign pleural effusions, were consistent with an immediate reaction triggered by intense asbestos exposure.

Desmoplastic malignant mesothelioma: a review of 17 cases

AIMS

To identify the histological features of desmoplastic mesothelioma, and to determine its incidence and prognosis.

METHODS

Two hundred and fifty five cases of malignant mesothelioma were examined over seven years (1982-9) to identify the desmoplastic variant. Sections were cut at 5 microns and stained with haemotoxylin and eosin and with CAM 5.2 (Dakopatts). Asbestos fibre counts were carried out by light microscopy in 14 cases using the potash digestion method.

RESULTS

Seventeen cases were identified as desmoplastic mesothelioma giving an incidence of 6.6%. In 11 cases the cell type in more cellular areas was sarcomatous and in six others it was biphasic. The mean survival time from onset of symptoms to death was 5.8 months for the sarcomatous variant and 6.8 months for the biphasic variant. Twelve of 16 patients had had previous occupational exposure to asbestos, ranging from five months to 43 years. The diagnosis of desmoplastic mesothelioma was only accepted if acellular connective tissue comprised 50% or more of the tumour bulk. Also seen was collagen necrosis, anastomosing bands of often hyalinised collagen with a prominent storiform pattern, and where cellular detail was present there were hyperchromatic nuclei.

CONCLUSIONS

Desmoplastic mesothelioma is a rare variant of malignant mesothelioma with a storiform collagen pattern, collagen necrosis, bland acellular collagen and focal cytological features of malignancy. Though rare, it is important to recognise this variant and distinguish it from a pleural plaque, nonspecific reactive pleural fibrosis, pleurisy, rheumatoid disease, or, rarely, spindle cell sarcomas.

Fibre distribution in the lungs and pleura of subjects with asbestos related diffuse pleural fibrosis

The lungs from 13 cases of diffuse pleural fibrosis associated with a history of exposure to asbestos were examined. Samples were taken from the visceral pleura and central and subpleural zones of the lungs for histopathological and mineralogical studies. The fibre type, size, and number were estimated for each of these regions by transmission electron microscopy and energy dispersive x ray analysis. Amphibole fibre counts were raised when compared with a non-occupationally exposed group and matched those seen in cases of pleural plaques, mild asbestosis, and mesothelioma. A wide case to case variation of distribution was seen. No significant difference was apparent between central and subpleural zones, whereas low asbestos counts were found in the pleura; these were mainly short chrysotile fibres. Within the lungs more (45%) of the longer (greater than 4 microns) and thinner (less than 0.25 micron) amphibole fibres were retained in keeping with other studies implicating such fibre profiles in the pathogenesis of asbestos related disease.

Asbestos induced pericardial effusion and constrictive pericarditis

The number of disorders attributable to asbestos exposure has increased gradually over the years. The latest to be recorded is pericardial effusion and constrictive pericarditis, and three cases are reported here. A man with bilateral pleural thickening and plaques developed acute pericarditis and an effusion and was treated by pericardiectomy. Two men died from constrictive pericarditis associated with bilateral pleural effusions and diffusion pleural thickening. The pericardium showed nonspecific fibrous thickening. All had been occupationally exposed to asbestos. In the fatal cases the lungs contained amphibole fibres, in keeping with a modest degree of occupational exposure. Asbestos produces progressive fibrosis of the pericardium that is similar to diffuse pleural thickening and may be fatal. Both conditions may develop after relatively short or light exposure.

Cellular and molecular basis of the asbestos-related diseases

Asbestosis is an inflammatory and fibrotic process of the alveolar structures mediated, at least in part, by cytokines released by "activated" alveolar macrophages. The process of phagocytosis and "activation" of alveolar macrophages is poorly understood. Are all macrophages activated or only subpopulations? Which cytokines are up-regulated? How does the local milieu modulate profibrotic and antifibrotic mediators? Is protein release accompanied by up-regulation of gene transcription? Is there an ordered sequence of cytokine activity? What roles do neutrophils and lymphocytes play? How can disease progression best be quantified absent further exposure? Answers to these questions are important to direct rational strategies at interdicting the fibrotic process. The question of cancer and asbestos is more vexing. The processes of inflammation, fibrosis, and carcinogenesis appear to be closely intertwined. For example, proto-oncogenes such as c-sis (PDGF B-chain) are up-regulated in activated alveolar macrophages from fibrotic lungs; these and possibly others may play an important role in asbestos carcinogenesis. Second, asbestos can transfect DNA into cells. Furthermore, DNA can adhere to asbestos fibers, and these fibers are capable of direct transmigration into cells. The questions of the mechanisms of cigarette smoke cocarcinogenicity and latency remain. Lastly, if the bronchial epithelium is highly metaplastic throughout from cigarette smoking, what triggers a single (or several) nidus of cells to transform into carcinoma? Malignant mesothelioma poses the most challenging questions because of association with brief asbestos exposure by history. Mesothelial cells are susceptible to minute environmental manipulations, and changes occur after exposure to all fiber types. Yet epidemiologic studies point toward long amphiboles as having greater mesothelioma risk. To test this hypothesis, experimental data must be generated differentiating tumorigenesis risk from short, chrysotile fibers that can migrate to the parietal pleura from the associations of long amphiboles persisting in lung tissue. Despite the future decreasing numbers of clinical cases of asbestos-related disease, solving the important mechanistic questions remaining will contribute significantly to our understanding of fibrosis and cancer.

Inflammation of the visceral pleura, a nonspecific asbestos-related pleural reaction: chest radiograph and computed tomograph correlation

Nonspecific pleuritis, i.e., inflammation of the visceral pleura, is recognized by the presence of pleural strands on the routine posteroanterior chest radiograph. The computed tomograph counterparts of these strands are seen as interlobular septal intrusions and lenticular or wedge-shaped subpleural opacities. The pleural reaction is nonspecific and may be found with asbestos exposure, traumatic hemorrhagic effusions, pulmonary embolism, viral pleurisy, malignant pleural effusions, and lupus or rheumatoid effusions. The asbestos-related pleural changes may be found alone or in association with parietal pleural plaque formation or with asbestotic lung fibrosis.

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.

Role of asbestos and other fibres in the development of diffuse malignant mesothelioma

Images

Human disease consequences of fiber exposures: a review of human lung pathology and fiber burden data

Inhalation of asbestos fibers results in a variety of neoplastic and nonneoplastic diseases of the respiratory tract. Some of these diseases, such as asbestosis, generally occur after prolonged and intensive exposure to asbestos, whereas others, such as pleural mesothelioma, may occur following brief exposures. Inhalation of nonasbestiform mineral fibers can occur as well, and these fibers can be recovered from human lung tissue. Thus, there has been considerable interest in the relationship between mineral fiber content of the lung and various pathologic changes. Techniques for fiber analysis of human tissues have not been standardized, and consequently results may differ appreciably from one laboratory to another. In all reported series, extremely high fiber burdens are found in the lungs of individuals with asbestosis. Although there is a correlation between the tissue concentration of asbestos fibers and the severity of pulmonary fibrosis, further studies of the mineralogic correlates of fiber-induced pulmonary fibrosis are needed. Mesothelioma may occur with fiber burdens considerably less than those necessary to produce asbestosis. More information is needed regarding the migration of fibers to the pleura and the numbers, types, and dimensions of fibers that accumulate at that site. Patients with asbestosis have a markedly increased risk for lung cancer, but the risk of lung cancer attributable to asbestos in exposed workers without asbestosis who also smoke is controversial. Combined epidemiologic-mineralogic studies of a well-defined cohort are needed to resolve this issue. In addition, more information is needed regarding the potential role of nonasbestos mineral fibers in the pathogenesis of lung cancer.

The value of ear lobe oximetry in the assessment of disability in asbestos-related disease

Thirty-four asbestos workers, with either asbestosis, diffuse pleural thickening, calcified pleural plaques, or with comparable asbestos exposure but no evidence of asbestos-related disease and seven normal controls underwent a progressive exercise test. The subjects were categorized on the basis of lung function tests and PA chest X-rays. During the exercise test oxygen saturation was measured continuously by an ear lobe oximeter. The asbestosis and diffuse pleural thickening groups showed significant oxygen desaturation on exertion, confirming that both these conditions give rise to appreciable respiratory disability.