CT&HRCT Concepts in Asbestos Screening

CT&HRCT Concepts in Asbestos Screening:

In general, there are 4 major lesions one is concerned about in general in asbestos CT/HRCT screenings:

  1. Is there asbestosis scarring of the lungs?
  2. Are there pleural plaques scarring of the chest wall lining?
  3. Is there a cancer or mesothelioma (a type of cancer of the chest wall lining)?
  4. Is there emphysema as an indicator of prior smoking?


HRCT is CT with thinner slices. CT often uses slice thickness of 3 to 10 mm I use 5 mm and HRCT uses 0.0625 to 2.5 mm thickness I use 1.25 mm thick slices.  Images can be processed in the lung views (called the windows and levels) for the sharpest detail of lung tissue information for interstitial lung disease/asbestosis and the chest wall/mediastinal views (called windows and levels) for the chest walls for plaques and for lung nodules/cancer. Studies can be done supine (lying on one’s back) which is good for plaquing, nodules and moderate to severe asbestosis and prone (lying on one’s stomach) which is the gold standard for identification of mild asbestosis if utilizing HRCT with lung views and given the thinner slices when utilizing the chest wall/mediastinal views, can at time define plaques including showing their calcifications better.


Asbestosis is scarring of lung tissue also called the interstitium or parenchyma.  it occurs initially at the back bottoms of the lungs bilaterally and the scarring is located in the far periphery, known as a subpleural location that is adjacent to the pleura (lining of the chest cavity). Classically asbestosis starts at the bottoms of the lungs, works its way up the sides and later the backs of the mid lungs and finally in later stages involves the backs, sides and fronts of the upper lungs – so it spreads from bottom to top. Initially it looks like a thin area of haziness, called intralobular interstitial thickening which may also have small perpendicular lines to the chest wall called short lines and sometimes small dotsWhen there are many short lines and dots, they can look net-like, often referred to as reticular. These areas of scarring are near microscopic and so we only see vague manifestations of their densities within (intra) the pulmonary lobules (lobular) small subdivisions of the lungs have scarring of lung tissue (interstitial) that gives vague densities due to very small areas of thickened tissue scarring (thickening). Sometimes, there can be fine curvilinear white lines that parallel the pleural surface, which when seen in the prone position (lying on ones stomach) in the back bottom of the lungs, is known as non-dependent (up in the air) subpleural (adjacent to the chest wall) line formation (little white lines). Later, one sees little black holes in the gray haziness due to small air tubes known as bronchioles being pulled apart (traction) by the scarring, known as traction bronchiolectasis. As more disease occurs, one can develop traction bronchiectasis dilatation of the medium size air tubes/airways due to their being pulled open wider by scarring pulling on them. Also, the ends of the air tubes (airways) have small tubes (respiratory bronchioles) with sacs attached to the tubes (small oxygen and carbon dioxide exchanging areas know as alveoli) and clusters of sacs (called alveolar sacs). Over time, with scarring, these structures can be destroyed leaving a cavity (honeycombing) having a scar perimeter and no viable tissue in the center. These holes, needing 2 to 3 in a row, to be called honeycombing, are subpleural and may, if with increased destruction, become multi-layered holes with well-defined walls.  Eventually, not only will there be distortion of the lung tissue, but also a vague haze may extend more centrally known as ground glass opacity. This is not a predominate finding and only occurs late in the disease progression (some people like to call the initial intralobular interstitial thickening ground glass, but I do not use the term this way and think it is misleading to say such, as other diseases have more ground glass which is either focal such as in early cancer (adenocarcinoma) or diffuse say in smoking related conditions (like desquamative interstitial pneumonia – DIP).


Pleural changes are numerous.  Pleural findings are called asbestos-related disease and not asbestosis which is reserved for the lung scarring. Early on, one can develop irritant fluid between the lung and chest wall known as a pleural effusion. Often, the pleural effusion is unilateral, but can be bilateral. Because the pleural effusion has blood and other components in the fluid, it is considered a sticky fluid collections (exudate). The pleural effusion can, in some, result in pain and can be heard with a stethoscope the problem called pleurisy by some, and the noise called a friction rub.  In most cases, this fluid is reabsorbed by the body and the problem goes away.  However, in some, the sticky fluid causes the lining of the lung (called the visceral pleura) and the lining of the chest cavity (called the parietal pleura) to stick together, scar and thicken (called diffuse pleural thickening).  Diffuse pleural thickening will limit the ability of the lung to expand in the areas where it is stuck to the chest wall and thus, can result in pulmonary (lung) function restriction (ability to blow out CO2 and take in O2), just like asbestosis (scarring of the lung), even if there is no asbestosis. With diffuse pleural thickening, the visceral (lining of the lung) pleura is thickened in addition to being scar fused to the parietal pleura (lining of the chest cavity). This visceral pleural thickening can be greater in areas and look triangular or elongated and crescent shaped and is known as a benign (not cancer) fibrotic [or cicatricial] (scarring) mass. Finger-like vertical projections can extend from the diffuse pleural thickening and project into the lung tissue, called parenchymal bands.  When, in some cases, these bands having extended outward, now fold in as if you were closing your extended fingers on your hand into a fist, they grab lung (on the inner side of the fingers) and compress that tissue into the center (like into the palm of a hand) of the now ball or fist like scar mass. This is called rounded atelectasis as it is round and represents a compression/collapse (the term atelectasis) of the lung into the center of the ball of peripheral collapsed and in-folded scar (parenchymal bands).  one can sometimes see blood vessels and/or airways curving into the center of this collapsing vortex and that is called the comet tail sign. Although rounded atelectasis can be obvious, sometimes a lung cancer can look identical and then PET/CT or biopsy may be necessary to separate them out.


Later, one develops scarring of the chest cavity lining including the chest wall (parietal pleura) known as pleural plaque formation. Any scar in the body, with time, can develop calcium deposits within it and as such pleural plaques can calcify over time.  The parietal pleura lining of the chest cavity is given different names at different locations, although all part of the same lining.  The back of the chest cavity is known as posterior face-on or en face (as if you are looking directly at that individual and that individual is facing you; if on the anterior chest wall, it is call anterior face-on or en face; on the lateral chest walls, it is call in-profile (as if you were looking at the person from the side or their in profile appearance); if more centrally, adjacent to the spine, it is call paravertebral; around the heart it is called pericardial and occasionally there will be other locations.  Note that the heart is made of muscle, and it has an outer lining called the pericardium. But, over the pericardium is the sac that covers the entire inside of the chest cavity and that portion of the sac that is in the midline, covers the heart and is known as the pericardial portion of the parietal pleura.  So, when a plaque occurs on the heart, it is not on the heart muscle or the heart lining, the pericardium, but rather involves the pericardial pleural that lies over the pericardium.


Lung cancers are fast growing abnormal cells that involve the lung tissue and can be called nodules that are round, ovoid or varying shapes, they can be smoothlobulated (lumpy bumpy), spiculated (like with rays of the sun extending from them). The nodules can be hazy ground glass opacities, hazy with some central density partial solid or solid. They can have central areas of dead tissue called central necrosis or can have holes in the center called cavitations. Also, they can be infiltrative ill defined, elongated or irregular densities that may or may not follow air tubes or may be solid and look like a pneumonia that does not respond to antibiotic therapy, called a consolidation.  Alternatively, one can have malignancies (cancers) of the chest lining called a mesothelioma, adenocarcinoma or metastases (spread of cancer from a distant lung mass or other body site).


Emphysema is due to destruction of the air exchange portions of the lung tissue and depending on the amount and where it occurs it has different appearances and different names. As opposed to asbestosis, emphysema spreads in the opposite direction from top to bottom. The main types with smoking are centrilobular looking like Swiss cheese with central holes in the lungs and paraseptal along the margins of the chest walls or adjacent to the mediastinum (adjacent to the heart, aorta or great vessels) or adjacent to the fissures (areas demarcating separations of the lung segments). An individual with a smoking history can have either or both types together.  There is also the panlobular type large areas of lung destruction involving both the areas by the chest wall and the central portions of the lungs as areas of significant void of lung structure. This can occur with smoking, but is predominant in a genetic condition called alpha 1, anti-trypsin deficiency and is more common in the lower lobes.


The above article is provided as a public service by Daniel Powers, M.D.: B-Reader, Board-Certified Diagnostic Radiologist, Certified by the American Board of Radiology.

If you detect any errors, have additional information to point me to, use other useful terms or have comments, please do e-mail them to me at



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