The official ILO grading of the profusion or the amount/quantity of interstitial and pleural disease relates to chest x-rays. In general, CT and HRCT with their cross sectional imaging capability are more accurate and definitive in showing imaging markers of asbestos disease than chest x-rays with its lesser resolution and overlap of structures, made even worse in the heavy set individual.
Supine spiral CT and supine HRCT scans can quantify, none (0/0), moderate (2/2) to severe (3/3) profusion and the Prone HRCT scan can quantify, none (0/0), mild (1/0, 1/1), moderate (2/2) and severe (3/3) profusion or lesser or greater variations of such amounts, into parallel profusion scores, similar to chest x-rays, based upon peer reviewed articles, textbook examples and continuing medical education credit lectures, although there are no ILO based standard CT/HRCT images for such, yet. Plaquing is better identified, as are their calcifications plus other pleural based lesions are better seen by CT or HRCT.
Supine spiral CT and supine HRCT scans are primarily for the identification of plaques and other pleural based lesions, moderate to severe interstitial fibrosis, having the appearance and distribution of asbestosis (lung tissue or parenchymal scarring aka interstitial lung disease = ILD) and cancer or mesothelioma. They can identify moderate to severe interstitial disease, but not mild disease. Supine spiral CT and supine HRCT scans are obtained with the individual lying on his/her back. Because mild ILD in asbestosis occurs at the back bottom portions of the lungs, the posterior aspects of the lower lung zones, but, so does gravitational haze called “dependent density” (density at the dependent or lower portions of the lungs), caused by a) atelectasis – partial collapse of the lungs due to the pressure of the anterior (front) portions of the lungs pushing down on the posterior (back) portions of the lungs and b) gravitationally-caused blood pooling – it becomes impossible to determine if the haziness at the back bottom portions of the lungs is due to gravity or ILD seen in asbestosis or both on supine studies.
Prone HRCT scanning is the study of choice for low profusion/mild ILD having the appearance and distribution of asbestosis. This scan is obtained with the individual lying on his/her stomach, the prone position, so the gravitational haze goes to the anterior or front portions of the lungs and the posterior or back portions of the lungs clear out, if only due to gravity, but maintain their haze, if there is ILD. If ILD is present, that can be classified by the B-reader (no standard images yet, but examples in many peer reviewed text books, journal articles and at lectures) into no = 0, mild = 1; moderate =2, or severe = 3 profusion or lesser or greater variations of such disease.
Concepts in Cancer Cases:
Chest x-rays are good for an overview of ILD, plaques and any lung cancer/mesothelioma.
In cancer cases, always try to obtain distant chest x-rays prior to or in the early stages of the lung cancer and prior to any chemotherapy or radiation treatment, to optimize visualization or lack thereof, of ILD having the appearance and distribution of asbestosis.
Supine Spiral CT and/or Supine HRCT (lying on one’s back), without contrast, are better than chest x-rays for the identification of plaques and their calcifications, lung cancer and features of mesothelioma identification and are usually excellent to show moderate to severe ILD having the appearance and distribution of asbestosis.
In cancer cases, since only 10 to 40% of plaques are seen on chest x-rays, if not seen or for more conclusive proof, supine spiral CT or frequently reformatted supine HRCT is used to look for the plaques and calcification in them and to confirm larger or to identify smaller lung cancers. They also differentiate chest wall fat from plaques and identify emphysema. Therefore, on any cancer case, one usually looks not only at the chest x-ray, but the CT as well, since plaques and/or their calcifications can be totally missed on chest x-rays, fat can mimic plaques and emphysema can be over looked. If moderate or greater profusion asbestosis is suspect, try to obtain the supine spiral CT, prior to the lung cancer or early on in its development, and before chemotherapy or radiation treatment (as they may or may not cause interstitial changes in and of themselves), but, if not available, any CT.
In cancer cases, prone HRCT is always ideal to have, but is seldom done as a routine procedure, and so, if the cancer case is new, there is suspicion for mild asbestosis and the individual can still cooperate for the exam, always try to obtain a prone HRCT without contrast, BEFORE chemotherapy or radiation treatment, to attempt to visually prove or disprove, the findings of mild asbestosis.
This article is provided as a public service by Daniel Powers, M.D.: B-Reader and Board-Certified Diagnostic Radiologist, Certified by the American Board of Radiology.
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