Chest X-ray interpretation: Clinical sciences

Chest radiograph, or chest X-ray, is one of the most commonly performed imaging studies, and can provide a large amount of useful information. So understanding how to approach and interpret a chest X-ray is an incredibly important clinical skill.

So the most common indications for a chest X-ray include chest pain, shortness of breath, or cough. It is also often used as a part of trauma and preoperative evaluation, and after placement of monitoring and support devices. 

While there are no absolute contraindications for a chest X-ray, and the radiation dose is small, you do want to ensure it is truly necessary, especially if your patient is pregnant.

Now, let’s discuss a systematic approach to interpreting a chest X-ray. This is going to involve checking the patient and study details, then assessing the quality of the study. Next, you want to scan the chest X-ray systematically and completely. You are looking to identify any abnormalities. Finally, you want to get a radiologist’s review of the film. Let’s go through each of these steps in more detail.

The first step in interpreting a chest X-ray is to check the name and date of birth on the image to confirm it’s the right patient, and the date and time to confirm it’s the right study.

Once you’ve done that, you are going to assess the quality of the chest X-ray. You’ll look at six main factors: projection, orientation, rotation, angulation, penetration, and inspiration. Remember, a good quality image gives you a lot of information, and a bad quality image could cause you to misinterpret findings. 

Begin with projection. Look to see how the film was taken. Is it a PA, or posterior to anterior, AP, or anterior to posterior, or a lateral study? The standard chest x-ray is PA. However, AP films are often seen when the patient needs a portable machine, like when they’re bedbound. Lateral films can be obtained with both.

Next, look at the orientation of the chest X-ray. Check the left and right markings. You’ll see a “L” or left marker on the right side of the image. Also the position of the patient is important. Supine means they’re laying down facing upward; lateral is when they’re laying on their side; semi upright is when their upper body is elevated 45 to 60 degrees from the bed; and upright is when they are sitting up at 90 degrees.

You then need to assess whether the patient is rotated toward their left or right. To do this, look at the relationship between the clavicles and the spine. If the medial ends of the clavicles are equidistant from the thoracic spinous process, the patient is not rotated.

Next, assess angulation, which is the angle that the X-ray penetrates the body. The clavicle should lay over the third rib, and only a small amount of the lung’s apex should be visible above the clavicle on a standard chest X-ray. 

Too little lung tissue and the shot is taken from below, means it’s angled upwards; while too much and the shot is taken from above, means it’s angled downwards.

Penetration is also very important. If a film is underpenetrated or overpenetrated, you may not be able to visualize important pathology. If the study is adequately penetrated, you should see the thoracic spine through the lower cardiac shadow.

The last quality metric you want to look at is inspiration. You should see eight to ten posterior ribs above the diaphragm. With poor inspiratory effort, you’ll see less than eight ribs, and may mistakenly think the resulting crowded lung markings represent a pathology.

Now, if your evaluation indicates a poor quality chest X-ray, you need to interpret it very cautiously. You can also repeat the study if needed.

Once you’ve assessed the quality of the chest X-ray, you are ready to “read” it. You want to scan the study systematically and completely. There are many methods to read a chest X-ray, but the important part is picking a system and using it consistently. This way, you will evaluate all structures and avoid skipping findings. 

For each chest X-ray, you must evaluate the mediastinum, hilum, trachea, lungs and pleura, diaphragm, bones and soft tissues, abdomen, as well as foreign bodies like support and monitoring devices.

As you systematically review the chest X-ray, you should identify any abnormalities and formulate a differential diagnosis for those abnormalities. If a previous chest X-ray is available, pull it up and compare findings. 

Also remember that radiological findings aren’t diagnostic, but they can help guide a differential diagnosis when correlated to the patient’s clinical picture. For instance, a pulmonary infiltrate in a patient with a fever can indicate pneumonia, while in a trauma case, it can indicate a pulmonary contusion.

While personally interpreting the chest X-ray is critical, you should also obtain a radiologist’s review of the study. Review the film with a radiologist, or look at the radiologist’s report once available.