Respiratory Therapy Cave: Tips for reading chest x-rays

To get a good idea of what's going on with our respiratory patients it's a good idea to look at chest x-rays. We RTs aren't expected, nor do we need to, be as proficient at reading them as a doctor, yet it's still a good idea to be able to see basic abnormalities.

This post is intended to simplify chest x-rays interpretation from an RT perspective. For the purpose of this post we will be looking at posterioranterior (AP) films. You should look at these as though the patient were standing right in front of you and facing you. Ideally you should have an older chest x-ray for comparison, although often this is not possible.

You can see the landmarks in a normal chest film below:

(a) A normal chest film with landmarks

(b) A normal chest film with lobes marked.

You should also note that the right diaphragm is 2/3 higher than the left. When these landmarks are not in their correct anatomical position this can indicate an abnormality. You should also observe that light bounces off solid objects causing these to appear white on the film. With this in mind, the following are true:

Gray is usually indicative of fat
Black is air
White is a solid object (bone, metal, mass, fluid, fibrotic tissue)

Most lung diseases are associated with an increased density within the interstitium, the air spaces or both. Increased density is generally seen as white, or increased whiteness of the lung fields, or more whiteness than what is normally present on a chest x-ray**.

Now that you have the basics down, you will want to have a "systemic approach" in looking at these films. Each radiologist may have his own system, yet a common one is as noted below: Note that this post is from an RT perspective, so I may have left one or two steps out.

1. Check the Airway: Is the trachea mid line? If it is shifted this could indicate an abnormality as you can see in this post. You'll want to observe the Carina, which is where the trachea bifurcates. It should normally be midway between the clavicles or over the spine at the 6th posterior rib or T4. The ETT should be 2 cm above the carina. The spine should go down the middle of the air column, and shifts may indicated scoliosis, kyphoscoliosis or other spinal disease that may cause a lung restriction.

2. Check bones: I'm not going to go into detail what to look for here. Bones should typically appear white. A break should be seen as a darker mark. If the bone appears darker or whiter it may be an indication of a disease process, such as a sclerotic bone may appear whiter. The ribs should be of equal distance apart. A narrow spacing between ribs may indicate paralysis on that side. Severe coughing can cause rib fractures, and this may be see on the 6th through the 9th ribs***

3. Check the heart: A normal heart size should occupy half of the left lung. If it's greater than this you have some degree of cardiomegally. If the heart looks like a water bottle this could be indicative of a pericardial effusion. The right heart should show up as two bulges in the right middle lobe. If they are not present this could indicate a pneumothorax of the right middle lobe***.

4. Check the diaphragm: A flat diaphragm may indicate hyper inflated lung, which may be indicative of emphysema or severe asthma attack. A flat diaphragm can easily be spotted if you see that the left and right diaphragm are at the same level.

5. Check the costrophrenic Angles: These are the angles of the lower left and lower right of the lungs. The angle is normally sharp. If it is blunted or rounded, this is indicative of a pleural effusion. It may also be blunted with heart failure. This angle is blunted because gravity pulls fluid down**.

6. Check the lung fields: You should be able to see the air passages as they branch from the trachea, bronchi, bronchioles. The smaller air passages and alveoli should not be visible. However, certain conditions will make them visible, such as pneumonia, atelectasis, pulmonary edema, pulmonary fibrosis, etc.

Fluid in lung tissue may cause a thickening of tissues of the air passages, and this may cause the passages to show up more clearly (they will be whiter). Depending on where they are in the lung will help determine the cause (although it's mostly a guess based on the patient's presentation and history). If it's isolated to one area of the lung it may be a lobar pneumonia. If it's in both lungs, like in both lung bases, it may be indicative of heart failure (pulmonary edema).

Things to look for in the lung fields:

(d) White arrows point at atelectic regions

A. Atelectasis: Usually looks like a white linear (straight) line. It's the most common finding, and is often caused by mucus plug or tumor. You can see a good example in picture c.
B. Consolidate: Solid white that you cannot see through. You cannot see landmarks. If it is isolated to one region of the lung, or is circular, it may be indicative of a lung mass. It could also be a really bad pneumonia.
C. Infiltrates: When fluid builds up in the interstitial walls of the bronchioles and alveoli, these make these air passages appear whiter than usual. Since only the air passages are white, you should still be able to see the landmarks behind them. Thus, infiltrates are patches of whiteness that you can see through. It's generally described as patchy, or patchy infiltrates. It's indicative pneumonia if it's isolated to one region of the lung. If it's in both regions (such as both bases) it could be indicative of fluid build-up due to heart failure.

(e) White arrows point at consolidation

D. Air bronchograms:
E. Pleural thickening: Fibrosis of the pleura indicated by a white line around the pleural region. It's almost always preceded by a pleural effusion, and causes a restirction *
F. Peribronchiolar thickening: This is
G. Silhouette sign: When you cannot see the "silhouette" of the lung markings due to whiteout (infiltrates or consolidation) due to fluid buildup or a mass in the normally air filled lungs. See figure g. In this figure the whiteout (opacity) is pneumonia.
H. Air bronchogram: Usually the smaller airways and the alveoli are not visible on the chest-x-ray. Certain disease conditions cause the tissues that surround the bronchi and the alveoli to become opacified (white). This makes it so you can easily see the outlines of these parts of the lungs (you can clearly see the bronchial tree). It can be due to consolidation (fluid) from pneumonia, pulmonary edema, ARDS, alveolar cell cancer, lymphoma or sarcoidosis. See figure h.
Nodule: A circular opacity on the chest x-ray. It may be dicative of calcification and be comletely benign (as in scarring from a past pneumonia), or it could be cancer. See figure e for a good example of a nodule.
Kerey B lines: These are lines that are usually seen in the right lower lobe near the costrophrenic angle. They are perpendicular to the pleural space, are 2-3 cm long, and are horizontal in direction. They are indicative of congestive heart failure or pulmonary fibrosis.
Peribronchiolar cuffing: This is caused by thickening of the bronchiolar wall due to congestive heart failure. The bronchiolar walls become visible and appear as donut-like densities in the lung parynchema****
Fluid in fissures: Fluid may build up in the pleural between the lung lobes, and this will show up as a thickened fissure. This is marked on the x-ray as a fissure line greater than the thickness of a line drawn by a pencil. **** This is indicative of congestive heart failure
Pleural effusions: This is where fluid builds up in the pleural space. It's usually present when you see blunted costrophrenic angles. Large ones can be seen when you see a miniscus-like line on the x-ray. This can be indicative of various conditions, including cancers and congested heart failure.

7. Check the stomach: You should see an air (black) bubble just below the heart, and this is from air in the stomach. If it's absent or if you see more than usual air bubbles this may be indicative of certain processes.

8. Check the Hila: Note the shadows of the right and left pulmonary arteries. Since the left is higher than the right, the right hilum is higher than the right. Note that the area around the hilum is often referred to as the perihilar region.

9. Check for instraments: Any leads, IVs, central lines, pacers, etc. will show up on the x-ray.

(f) Red arrows point to the hilar region

In making your interpretation of the chest x-ray you'll want to make comparisons to any previous chest x-rays you may have. This will help you monitor the progression of the patient.

Likewise, you'll also need to know the age, assessment, and medical history of the patient. Plus you should consider other tests, such as laboratory tests, cat scans, etc. All of these together should help you paint a picture as to what might be wrong with your patient.