Thursday, July 30, 2009

How To Read A Chest X-Ray

Let's say you are trekking in the Himalayas and suddenly become short of breath. Even though you are on your way to Annapurna Base Camp in a remote corner of the world, you would most likely be taken to a local clinic and have a plain film chest x-ray taken of your chest to help determine the etiology of your dyspnea, just like in any other part of the world. This post is not a comprehensive account of how to read a chest x-ray, but rather a collection of tips and tricks that should help one read most plain chest x-ray films.


The Plain Film Chest X-Ray: PA And Lateral Views

While there are many possible views that can be taken of the chest, the two most common are the PA view and the lateral view. The PA view, or Posterior-Anterior view, positions the beam at the patient's back. The radiation then travels through the spine, lungs, heart, and finally skin until it meets the detector or film anterior to the patient. The advantage of a PA film over an AP, or anterior-posterior, view is a reduction in the enlargement of the cardiac silhouette. Since the heart is closer to the film, its shadow is less distorted.

The PA view is often taken simultaneously with a lateral view. The benefit of having two views is that the radiologist is better able to visualize abnormalities in 3-D space with two views. Otherwise, there is a chance that two abnormalities can be in the same sagittal plane, yielding only one shadow on the PA view. The lateral view would distinguish between these two lesions. In other words, the PA view tells you where things are, medial to lateral, while the lateral view tells you where things are in an anterior to posterior sense.


How To Read A Plain Film Chest X-Ray

There is no right or wrong way to read a chest x-ray, but it is beneficial to develop a systematic method of doing so. The first thing to always check is that the film is associated with the correct patient. After doing so, to read a PA view, I utilize a mnemonic called RIP ABCDEFGH. Here is how it works:

Rotation: Check to see that the patient is not rotated. You can look at the clavicles and make sure the vertebral processes line up nicely in between them.
Inspiration: Check to see that you can see about 9 ribs on each side. Less than 8? It is likely poor inspiration.
Penetration: You should be able to see lucencies in the middle of the film representing the intervertebral discs. If there are none, the film is over-penetrated; if they are too well-defined, the film is under-penetrated.

Airway: Trace the lucency from the neck down towards the carina. It should be midline and you should be able to see two bronchi splitting from it.
Bones: Look at the shoulder joint and trace out each rib contour to check for fractures or other abnormalities.
Cardiac Silhouette: Check the right and left heart borders.
Diaphragms: These should be well-defined with no obscuration of their margins.
Empty Space =)
Fields: Look at the lung fields bilaterally and compare. Don't forget the apices.
Gastric Bubble: Check for a lucency in the left upper abdominal quadrant.
Hardware: Make sure the placement of any lines or other hardware is appropriate.

Pretty simple, no? After going through this process several times, it becomes routines. You can then use the lateral view to confirm your findings. Develop a process for evaluating lateral films as well, but in general, they are used to confirm what is seen on the PA view. While simple, learning how to read a chest x-ray is a basic skill all radiologists should know well before moving on to reading more advanced imaging, even in the remote reaches of Nepal =)

For patients, there are several advantages to using x-rays when possible, including lower radiation doses, faster acquisition times, and lower total cost. Often, the cost of x-rays will be covered by the patient's health insurance provider. This can be a significant issue, especially for patients who do not have great access to care.