Center for Asbestos Safety

Pathology of Asbestosis

Microscopic evaluation of lung tissue is only rarely required to make a diagnosis of asbestosis. The unpleasant anatomic characteristics of the disease include the development of small, stiff lungs with fibrosis within the subpleural parts of the lower lobes. The adjoining visceral pleura can also become fibrotic and may be linked with parietal pleural plaques, while there is generally a relative sparing of the central regions of the lung.

In case of a histopathologic diagnosis of asbestosis, the presence of coated or uncoated asbestos fibers (asbestos bodies) is required in association with interstitial pulmonary fibrosis which appears similar to usual interstitial pneumonitis (UIP).

Asbestos bodies – These are composed of transparent fibers of asbestos enclosed by a coating of protein and iron. This type of coating can enclose a variety of other mineral particles, for instance, talc, carbon, iron or glass. The resulting structures are collectively referred to as ferruginous bodies. An accurate identification of the mineral enclosed within a ferruginous body cannot be achieved with light microscopy. For definitive identification, scanning electron microscopy may be required with energy dispersive x-ray evaluation of lung specimens. Amphibole asbestos fibers form asbestos bodies more frequently as compared to chrysotile fibers, partly due to reduced pulmonary clearance of amphiboles.

The amount of asbestos fibers deposited in the lungs (including both coated and uncoated) is usually 10-20 times more among asbestosis patients in comparison to unexposed individuals. The deposited quantity of asbestos correlates with the extent and magnitude of fibrosis. Measurement of asbestos bodies using light microscopy underestimates the total lung fiber burden by a significant percentage. The total number of asbestos bodies in digested lung is usually 10 to 10,000 times less as compared to the total number of uncoated fibers detected by electron microscopy.

Bronchoalveolar lavage – The overall burden of parenchymal asbestos fibers is demonstrated by the total number of these fibers present in the sputum and bronchoalveolar lavage (BAL) fluid. Asbestos workers diagnosed with asbestosis have increased numbers of asbestos bodies in their sputum and BAL fluid in comparison to asbestos workers who have a normal chest radiograph. In patients with suspected asbestos-related disease, more than one asbestos body per mL of BAL fluid is indicative of more than 1000 asbestos bodies for every gram of lung tissue. Such levels are linked with significant exposure.

However, the clinical utility of measuring asbestos bodies in tissues and BAL fluid is limited. It is difficult to interpret the results due to marked interpatient variation and also because of the fact that considerable amounts of asbestos fibers may be present in exposed, but disease-free individuals.

Diagnosis of Asbestosis

Given below are 3 major findings that help validate the diagnosis of asbestosis:

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