Making a Diagnosis:
There are three ways to make a diagnosis.
A) Clinical Diagnosis: Such as from the occupational history of exposure, pulmonary function tests, the clinical examination and the composite of other laboratory or consulting work.
B) Pathologic or Histologic Diagnosis – based upon findings seen on gross tissue specimens and/or microscopic, including electron microscope analysis such as evidence for fibrosis, asbestos bodies, etc.
C) Imaging Diagnosis – based upon the imaging findings of asbestosis or asbestos-related disease by chest x-ray, CT, HRCT or PET/CT.
All three diagnoses contribute to the evaluation of the individual exposed and depending on the circumstances, any, some or all of the three may contribute more to a final determination of the specific disease diagnosis.
Can Asbestosis be Present Without Pleural Plaques?
First, it depends on what type of imaging study one is looking at. Chest x-rays see only 10% to 40% of plaques according to some peer-reviewed literature, meaning that 60% to 90% of plaques can be missed. Obviously, in those circumstances one can easily have asbestosis without visualizing the plaques. In addition, interstitial fibrosis/asbestosis can occur in individuals without plaque formation. This is not uncommon and it can occur in either early or moderate-to-severe disease. As a matter of fact, at the recent B-Reader re-certification examination in their teaching file, there were three cases with moderate-to-advanced profusion interstitial disease, having the appearance and distribution of asbestosis, but without plaques.
If the Histology is Negative, Can an Individual Still Develop Lung Cancer After Being Asbestos Exposed?
There are five concepts, as I understand it, some of which are based on imaging and some of which are addressed by other experts, that can explain this:
The Rotten Apple Concept – Missed Disease:
In this analogy, the majority of the apple is normal, but there is a brown spot on and within it. If one were to slice the apple, the majority of the slices would be normal and only the slice going through the brown spot would be abnormal. The same would hold true with imaging where skipped spaces are utilized or in histology where limited samples are obtained, if the amount of detectable disease is limited. If one that does not evaluate all the tissue, obviously asbestos bodies, asbestos fibers and evidence for fibrosis and/or pleural plaquing can be missed. Therefore, depending on the sample size and extent, there may be misses.
The Iceberg Theory – Microscopic Disease:
In this analogy icebergs have the majority of their mass below the water and only a small amount of their mass above the water. The same holds true with asbestosis (and can also be said about emphysema). It begins as a microscopic process of fibrosis (for emphysema as destruction of airways). Much fibrosis (microscopic destruction of airways) is necessary on a microscopic level, overlapping each other, before it becomes visible to the naked eye or macroscopic. Even with the thin slice HRCT scans, these are considered macroscopic findings. That is, if you were in the laboratory and cut open a lung, you could see the fibrosis with your naked eye, if adequate amounts were present. If they were only present on a microscopic basis, then they could not be seen. CT and HRCT scans do not represent microscopic imaging tests, therefore, an individual may have had asbestos exposure with significant microscopic asbestosis that has not yet become macroscopically visible and, therefore, even in the absence of visible imaging evidence for asbestosis this does not preclude a significant amount of microscopic asbestosis.
Chromosomal Changes Caused by Asbestos Exposure: Dr. Brody has presented information that I saw at the Perrin Conferences about two causes of lung cancer in asbestos exposure, as I understand him:
a) Advanced fibrosis in asbestosis and/or other interstitial lung diseases are often associated with increased risk of lung cancer.
b) However, in addition, asbestos fibers are chemotoxic and can cause chromosomal damage to tissues within the respiratory tract resulting in the development of lung cancer without the presence of fibrosis in the lung/asbestosis or pleural plaques. Therefore, the absence of asbestosis did not negate the chemotoxic effects of the inhaled asbestos fibers that can result in asbestos-caused lung cancer.
Asbestos Fiber Removal/Dissolution: There is some evidence that Chrysotile is more likely to be attacked by the lung’s defense system and removed and/or dissolved. As such, the toxic/irritating effects of the asbestos fibers may have occurred even though on a histologic section there is no longer evidence for the fiber and/or its residual asbestos body.
Smoking-Enhanced Asbestos-Caused Cancer Risk: If one smokes, as I understand it, there is a 6% chance of developing lung cancer (obviously this depends on the dose and duration of cigarette smoking) compared to the non-smoker population. My understanding is that when exposed to asbestos, there is a 4% to 5% chance of developing lung cancer (also dependent in part on the dose, duration and type of fiber exposed to) compared to the non-asbestos, non-smoker exposed population. However when a smoker is exposed to asbestos fibers, there is a 50 to 100 times greater incidence of lung cancer development compared to the non-smoker, nonasbestos population and given that asbestos fibers can cause lung cancer according to Dr. Brody without evidence for asbestosis, even with evidence for emphysema without visual evidence of asbestosis on imaging studies, but documented evidence of asbestos exposure, there is a substantial increase in the incidence of lung cancer potential.
The above article is presented as a public service by Daniel Powers, M.D., B-Reader and Diagnostic Radiologist, certified by the American Board of Radiology. It represents a general review of concepts. There may be other data and opinions on such.
If you detect any errors, have additional information to point me too, use other useful terms or have comments, please do email them to me at [email protected]
