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Patterns of Lung Disease in Chest Radiographs

March 5, 2009
Written by: , Filed in: Chest Radiology
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When looking at chest radiographs of the lungs, the challenge is that creating a two-dimensional representation of a three-dimensional structure is extremely problematic.

With that in mind, looking at the lung directly in cross-section without any superimposition of densities allows us to truly make distinctions with a much higher degree of reliability.

It makes sense as a first point of origin issue, when we see that the lungs are abnormal, that is a first level judgment. The lungs are not right; they do not look like they are supposed to.

The next question is, what is the main abnormality? Are there too many lines? Is it a kind of reticular process? Are there too many nodules in the lungs? Is the lung density abnormal?

Once you have made that judgment, then you need to think about what the true distribution of the disease is. That is the great advantage of high resolution imaging, because we have this unique ability to look at the basic, normal anatomy of the lung.

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What should we see in a normal study? Obviously, you see blood vessels, and you see airways.

The airways typically do not extend much about halfway from the hilum to the periphery of the lung. You do not see much beyond that, even with good high-resolution technique, because once you get out in the periphery, the airways have air in the lumen. In order to identify them, you need to be able to identify the bronchial wall.

As you go further out in the periphery, they become thinner and thinner, so that by the time you get into the periphery of the lung, the structures may be only 0.15 mm in thickness, and you cannot see them.

You will occasionally see linear structures, especially along the pleural surface, and those are the so-called secondary or interlobular septa that divide the main key anatomic structure of the lung, which is the secondary lobule.

You will see blood vessels as they course-out toward the periphery, but they get smaller as you track them along.

Typically a normal blood vessel will not reach the pleural space. It stops about half a centimeter or so from the pleural surface, and you may see one or two lines typically at the apex of the lung, occasionally toward the diaphragm, that represent the few normal interlobular septa that you may be able to identify.

When you are faced with abnormal lung, what do you expect to see? There are going to be additional extra lines, and if the extra lines are the primary abnormality, then you are dealing with reticular disease.

If there are too many nodules, you are dealing with a nodular disease process. There may be just too much density in the lung, so-called ground glass attenuation of consolidation, and there are disease processes that are primarily affected by that kind of air space pathology, and then there may be too many holes in the lung as in cystic lung disease.

There are probably around 140 to 150 different types of diffuse lung disease. The key is to first come to an anatomic decision about what you think is the primary abnormality, and then realize that for each of those,  there is really only a very limited differential diagnosis for each.

In fact, there are only about eight or 10 common diffuse processes in the lung that someone even in most academic centers, are likely to encounter.

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