Sunday, September 20, 2009

How to read a chest X Ray: The easiest way to read a CXR

These are just some simple tips for medical students on reading chest X Ray. Of course, if want to give a full comment about an X-ray you will have to comment on the quality of the film, postioning, the view(PA, AP or lateral), wether it's an inspiratory or expiratory film, etc.

But in this article I'll only mention hwo you can reach a clinical diagnosis for an X-ray and what are the basics you need for a chest X-ray interpretation and to identify some of the common chest lesions in radiology. Most of the CXR you will see are just plan x rays.

As a rule : Air in X-rays appears black while tissues appears whitish/greyish (hyperdense) the harder the tissue (such as bone) the more dense (white) it appears. The main structures in a CXR are the: lung parynchema, trachea, diaphragm, hear, bones and mediastinal shadows.
To make this as simple as possible let's divide lesions into groups:

I)White opacities:

  1. A-Homogenous: a homogenous or a continuous opacity (whitish) may refer to a consolidation or a fluid and it's not well defined. If the costophrenic angle is obliterated and the shadow is rising to the axilla, that's a typical pleural effusion.

    Opacities inside the lung parynchema (with a free angle) is more propably lobar pneumonia.

    Lobar pneumonia in the upper zone
There are many features to differentiate types of pneumonia but you can learn about this later, remember that T.B. shadows are most common in the upper lung zones

Pleural Effusion

  1. B-Heterogenous opacities:
    Usually, if these opacities are multiple, rounded with well defined borders (nodules or masses) they are malignant (cannon ball metastasis).
    also shows a heterogenous opacitiy but it's bilateral, patchy, scattered and not well defined.
    Miliary T.B. Shadows will appear like small numerous fine dots.

    II)Black opacities: (air):

    Either it's inside the lungs or outide (in the pleural cavity).
    The increased air inside the lungs in cases of emphysema (hyperinflation) will have visible bronchovascular markings and a flat descended diaphragm.

    Air in the pleural space (pneumothorax) is referred to in some books as (jet black) which means it has no vascular markings and if it is large enough to compress the lung, the collapsed lung will be apparent in the film. It may be mixed with a fluid (serous fluid, pus, blood) and then it will show an air fluid level (hydropneumothorax).


    A well defined circular cavity in the lung parynchema may be either a lung abscess (which show a fluid level) or it may be empty in case of pneumatoceles in some types of pneumonia.

Of course, there are many other aspects to consider but this is just a short introduction for beginners to summarize things up.
Also, remember the famous mnemonic about the items you should look at in a CXR :
A: Airways
B: Bones
C: Cardiac shadow
D: Diaphragm
E: Empty spaces
F: Fields of the lung
G: Hilar regions

You can also search for another approach to classify chest X rays the way you like, i tried to demonestrate the easiest way for me, others may like to classify the lesions to (alverolar, interstitial, pleural, etc), use the most memorable and systematic method and stick to it.