Radiography
Asbestosis. Posteroanterior chest radiograph reveals a few reticulonodular opacities at the lung bases consistent with mild asbestosis.
Asbestosis. Posteroanterior chest radiograph in a 54-year-old man with asbestosis demonstrates coarse linear opacities at the bases more prominent on the left, obscuring the cardiac borders and diaphragm (shaggy heart border sign).
Findings
Techniques and findings
The characteristic finding in asbestosis is the presence of small irregular opacities, usually in the mid and lower lung zones (see top Image above and Image 1 in Multimedia). According to the 1980 International Labour Organization classification,8 "small irregular opacities" describe irregular linear shadows that develop in the lung parenchyma and obscure normal bronchovascular markings.
The progression of disease is divided into 3 stages.
- In the first stage, a fine reticular pattern may be seen, usually at the lung bases, in association with a ground-glass appearance, which may represent a combination of alveolitis and interstitial fibrosis.
- The second stage is characterized by progression of the small irregular opacities into a prominent interstitial pattern. During this stage, a combination of parenchymal and pleural abnormalities may partially obscure the heart border (shaggy heart sign; see second image above and Image 2 in Multimedia) and diaphragm.
- In the last stage, progression of the coarse interstitial pattern and honeycombing to the upper lung zones occurs, along with further obscuration of the heart and diaphragm
Accuracy
- The radiographic findings described above are rather nonspecific, which may lead to a high false-positive rate, but the presence of pleural abnormalities and a compatible clinical history would increase the specificity of the diagnosis of asbestosis.
- Estimates of the sensitivity of chest radiography in the detection of asbestos-related interstitial fibrosis vary widely from 40-90%.
Imaging pearls
- Conventional radiographs are relatively insensitive in the detection of early asbestosis and tend to underestimate the severity of disease.
Computed Tomography
Asbestosis. High-resolution CT scan through the mid lung zone demonstrates a parenchymal band on the left (arrow).
Asbestosis. High-resolution CT scan more inferiorly reveals subpleural curvilinear opacities bilaterally (white arrows) and thickened interstitial lines (black arrows).
Asbestosis. High-resolution CT scan through the lower lung zone nicely demonstrates thickened septal lines (white arrows) and small rounded subpleural intralobular opacities (black arrow). Also note the calcified diaphragmatic pleural plaque on the left.
Findings
Techniques and findings
Common high-resolution computed tomography (HRCT) findings in early asbestosis are intralobular, small, rounded or branching opacities; thickened interlobular septa; subpleural curvilinear lines; and parenchymal bands. The interlobular septal lines typically represent fibrosis. With progression of disease, honeycombing is seen. Similar to the radiographic appearance, the findings described above predominantly involve the subpleural regions of the lower lung zones. As most of the abnormalities seen in mild asbestosis may be confined to the posterior basal lung zones, the CT study should include images with the patient in the prone position to differentiate normal dependent parenchymal opacity from mild subpleural fibrosis.
The earliest lesions observed on HRCT indicating fibrosis are believed to be subpleural intralobular rounded or branching opacities, which correspond to peribronchiolar fibrosis, the earliest microscopic finding. Theoretically, prior to fibrosis, a ground-glass appearance involving the air spaces may indicate alveolitis.
Subpleural lines, which also are present early on, are curvilinear opacities observed parallel to and within 1 cm of the pleura. They are usually 5-10 cm long and likely represent a combination of peribronchiolar fibrosis and atelectasis.
Parenchymal bands are thick linear 2-5 cm long opacities that course through the lung and contact the pleural surface. These correspond to fibrosis along a bronchovascular sheath or interlobular septa with architectural distortion.
Honeycombing is characterized by thick-walled multiple cystic spaces smaller than 1 cm in diameter.
Accuracy
- With its ability to show lung abnormalities not appreciated on conventional radiographs, CT is considerably more sensitive than conventional radiography for detecting asbestosis, especially for early or mild disease.
- In particular, the advent of HRCT has further improved sensitivity.
- As with radiography, CT findings in asbestosis are nonspecific, and the identification of a single abnormality is not diagnostic. One study assessing the accuracy of HRCT in asbestos-exposed individuals demonstrated 100% specificity when at least 3 of the abnormalities described above were present on the scans.9 However, the exceptionally high specificity came at the expense of a decreased sensitivity (56% when 3 findings were present). The converse holds true as well: diagnosis based on 1 or 2 abnormalities increases sensitivity but decreases specificity.
Magnetic Resonance Imaging
Findings
- Currently, the role of MR imaging in the diagnosis of asbestosis is limited.
- A 1998 study showed MR to be more sensitive than chest radiography in detecting subclinical asbestosis.10
- A 2004 study found that MR imaging compared favorably with CT for detecting asbestos-related pleural disease.11
Nuclear Imaging
Findings
- Before HRCT gained popularity, gallium-67 scans were often helpful in diagnosing asbestosis in patients with appropriate clinical presentations but normal or equivocal chest radiographs.
- Gallium-67 scans are usually positive in patients with asbestosis and may even provide a measure of inflammatory activity because the isotope is believed to be engulfed by alveolar macrophages.
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References
National Center for Health Statistics. Asbestosis: Death rates (per million population) by race and sex, U.S. residents age 15 and over, 1995–2004. Available at http://www2a.cdc.gov/drds/WorldReportData/pdf/2007T01-02.pdf. Accessed November 21, 2008.
National Center for Health Statistics. Asbestosis: Number of deaths by sex, race, and age, and median age at death, U.S. residents age 15 and over, 1995–2004. Available at http://www2a.cdc.gov/drds/WorldReportData/pdf/2007T01-01.pdf. Accessed November 21, 2008.
Antao VC, Pinheiro GA, Wassell JT. Asbestosis Mortality in the United States: Facts and Predictions. Occup Environ Med. Nov 18 2008;[Medline].
Bang KM, Mazurek JM, Syamlal G, Wood JM. Asbestosis mortality surveillance in the United States, 1970-2004. Int J Occup Environ Health. Jul-Sep 2008;14(3):161-9. [Medline].
National Institute for Occupational Safety and Health. Chest Radiography: B Reader Information for Medical Professionals. Centers for Disease Control. Available at http://www.cdc.gov/niosh/topics/chestradiography/breader-info.html. Accessed November 24, 2008.
Stayner L, Kuempel E, Gilbert S, Hein M, Dement J. An epidemiological study of the role of chrysotile asbestos fibre dimensions in determining respiratory disease risk in exposed workers. Occup Environ Med. Sep 2008;65(9):613-9. [Medline].
Hessel PA, Gamble JF, McDonald JC. Asbestos, asbestosis, and lung cancer: a critical assessment of the epidemiological evidence. Thorax. May 2005;60(5):433-6. [Medline].
International Labour Office. Guidelines for the use of the ILO International Classification of Radiographs of Pneumoconioses. Revised Edition 2000. Occupational Safety and Health Series. No.22. Geneva: International Labour Office; 2000.
Gamsu G, Salmon CJ, Warnock ML. CT quantification of interstitial fibrosis in patients with asbestosis: a comparison of two methods. AJR Am J Roentgenol. Jan 1995;164(1):63-8. [Medline].
Bekkelund SI, Aasebo U, Pierre-Jerome C. Magnetic resonance imaging of the thorax in the evaluation of asbestosis. Eur Respir J. Jan 1998;11(1):194-7. [Medline].
Weber MA, Bock M, Plathow C, Wasser K, Fink C, Zuna I, et al. Asbestos-related pleural disease: value of dedicated magnetic resonance imaging techniques. Invest Radiol. Sep 2004;39(9):554-64. [Medline].
Akira M, Yamamoto S, Yokoyama K. Asbestosis: high-resolution CT-pathologic correlation. Radiology. Aug 1990;176(2):389-94. [Medline].
Becklake MR, Cowie RL. Environmental and occupational disorders. Textbook of Respiratory Medicine, 3rd edition. 2000;1830-37.
Billings CG, Howard P. Asbestos exposure, lung cancer and asbestosis. Monaldi Arch Chest Dis. Apr 2000;55(2):151-6. [Medline].
Fraser RS, Muller NL, Colman N. Inhalation of inorganic dust (pneumoconioses). Fraser and Pare's Diagnosis of Diseases of the Chest, 4th edition. 1999;2386-2484.
Fujimura N. Pathology and pathophysiology of pneumoconiosis. Curr Opin Pulm Med. Mar 2000;6(2):140-4. [Medline].
Kamp DW, Weitzman SA. The molecular basis of asbestos induced lung injury. Thorax. Jul 1999;54(7):638-52. [Medline].
Levin SM, Kann PE, Lax MB. Medical examination for asbestos-related disease. Am J Ind Med. Jan 2000;37(1):6-22. [Medline].
McLoud TC. Conventional radiography in the diagnosis of asbestos-related disease. Radiol Clin North Am. Nov 1992;30(6):1177-89. [Medline].
Mossman BT, Churg A. Mechanisms in the pathogenesis of asbestosis and silicosis. Am J Respir Crit Care Med. May 1998;157(5 Pt 1):1666-80. [Medline].
Rom WN. Asbestos-related lung disease. Fishman's Pulmonary Diseases and Disorders, 3rd edition. 1998;879-887.
Staples CA. Computed tomography in the evaluation of benign asbestos-related disorders. Radiol Clin North Am. Nov 1992;30(6):1191-207. [Medline].
Wagner GR. Asbestosis and silicosis. Lancet. May 3 1997;349(9061):1311-5. [Medline].
Further Reading
Clinical trial
Early Diagnosis of Lung Cancer and Mesothelioma in Prior Asbestos Workers
Related eMedicine topics
Asbestosis (Pulmonology)
Asbestos-Related Disease (Radiology)
Mesothelioma
