Getting into the chest x-ray (part 4)—how pathology changes the grayscale

A normal chest x-ray has a certain grayscale pattern based on tissue density, geometry, interfaces, and overlap. When pathology occurs in the thorax, the pathology causes the normal grayscale of the chest x-ray to change in several ways. In this video from our Chext X-Ray Essentials course, Julian Dobranowski, MD will cover important concepts such as pneumothorax and pleural effusion in-depth, as he explains how pathology can change the grayscale of the x-ray image.

This is the final video in a 4-part series on chest x-ray problems:

• Watch video #1: The importance of grayscale
• Watch video #2: The importance of overlap
• Watch video #3: The importance of shapes and key landmarks

If you want to take your chest x-ray skills to the next level, then check out our Chest X-ray Essentials course, which was specifically designed for non-radiologists who want to use the chest x-ray in order to make better clinical decisions.

[00:00:00] What will I gain from this video? At the end of the video, you will know about the various ways that pathology can change the normal grayscale on a chest x-ray. Previously, we have learned that a normal chest x-ray has a certain grayscale pattern based on tissue density, geometry, interfaces, and overlap. When pathology occurs in the thorax, the pathology causes the normal

[00:00:30] grayscale of the chest x-ray to change in several ways. A normal gray structure can become too black or too white or a normally black structure can become gray or too white or a normally white structure can become gray or too black. Here, we have an example of a normal chest x-ray. If we focus on the left hemithorax, this is what normal looks like. In this example, here, we see that the left hemithorax is too white. The reason the left hemithorax is white is

[00:01:00] because the left lung is collapsed. On this example, here, we see that the left hemithorax is too black. The reason it is too black is because there's air outside of the lung. We will learn more about this in later presentations but what this patient has is a pneumothorax. And because the heart and the mediastinal structures are shifted to the right side, this is called a tension pneumothorax.

[00:01:30] The grayscale of the structure can stay the same, but the structure can increase or decrease in size. Here, we have an example of normal. If we focus on the central structures, we can see the normal appearance of the heart. On this example, we see that the heart is grossly enlarged. The normal thoracic aorta lies in this region. In this case, this interface

[00:02:00] that we are seeing is caused by a grossly dilated aorta, in this patient with a thoracic aortic aneurysm. The grayscale of the structure can stay the same but the structure can be displaced horizontally or vertically. Or the grayscale of the structure can stay the same but the shape of the structure can become distorted. Now, let's do some example cases. These are two x-rays of the same patient. If we look on this x-ray, we can identify that within the left

[00:02:30] side, inferiorly, there is an increased density. It's too white when compared to the normal x-ray on the left. The reason for this is because the patient has a left-sided pneumonia. On these two x-rays of the same patient, we see that there's a big difference. On this x-ray, we see this whiteness, inferiorly on the right and on the left side, which was not present on the previous

[00:03:00] examination. The patient has developed bilateral pleural effusions. In this case, we see that it is too black within this hemithorax as compared to the other x-ray, which is normal. The reason for that is because the patient has a pneumothorax. Because the heart and mediastinal structures are shifted to the right, this is classified and call as a tension pneumothorax.

[00:03:30] So in recap, the abnormalities within the thorax can be classified as too white, too black, the pathology can be too black and too white. And I'll explain how that can occur in a future video.