On a chest x-ray lung abnormalities will either present as areas of increased density or as areas of decreased density.
Lung abnormalities with an increased density - also called opacities - are the most common.
A practical approach is to divide these into four patterns:
Four pattern Approach
Whenever you see an area of increased density within the lung, it must be the result of one of these four patterns.
Here are the most common examples of these four patterns on a chest x-ray (click image to enlarge).
You have to realize that it is not always possible to divide lung abnormalities into one of these four patterns, but that should not be a problem.
Sometimes you are confronted with an abnormality that looks like a mass, but it could also be a consolidation.
Just do the work-up of both the differential diagnosis of masses and consolidation.
In such a case information from clinical data, old films or follow-up films and CT-scan will usually solve the problem.
Finally in some cases only biopsy will provide a diagnosis.
Consolidation is the result of replacement of air in the alveoli by transudate, pus, blood, cells or other substances.
Pneumonia is by far the most common cause of consolidation.
The disease usually starts within the alveoli and spreads from one alveolus to another.
When it reaches a fissure the spread stops there.
The key-findings on the X-ray are:
Differential diagnosisThe table summarizes the most common diseases, that present with consolidation.
Click to enlarge.
Chronic diseases are indicated in red.
A way to think of the differential diagnosis is to think of the possible content of the alveoli:
For instance a lobar pneumonia caused by streptococcus pneumoniae may become diffuse if the patient does not respond to the treatment.
Other examples are organizing pneumonia (OP) and chronic eosinophilic pneumonia.
These diseases typically present as multifocal consolidations, but sometimes they may become diffuse.
OP is organizing pneumonia. When it is idiopathic it is called cryptogenic (COP). The old name is BOOP - Bronchiolitis Obliterans Organizing Pneumonia.
The new name for BAC - bronchoalveolar carcinoma is adenocarcinoma in situ.
It is very important to differentiate between acute consolidation and chronic consolidation, because it will limit the differential diagnosis.
In chronic disease we think of:
Here a typical lobar consolidation.
First study the images, then continue reading.
The findings are:
At the borders of the disease some alveoli will be involved, while others are not, thus creating ill-defined borders.
As the disease reaches a fissure, this will result in a sharp delineation, since consolidation will not cross a fissure.
As the alveoli that surround the bronchi become more dense, the bronchi will become more visible, resulting in an air-bronchogram (arrow).
In consolidation there should be no or only minimal volume loss, which differentiates consolidation from atelectasis.
Expansion of a consolidated lobe is not so common and is seen in Klebsiella pneumoniae and sometimes in Streptococcus pneumoniae, TB and lung cancer with obstructive pneumonia.
On the chest x-ray there is an ill-defined area of increased density in the right upper lobe without volume loss.
The right hilus is in a normal position.
Notice the air-bronchogram (arrow).
In the proper clinical setting this is most likely a lobar or segmental pneumonia.
However if this patient had weight loss or long standing symptoms, we would include the list of causes of chronic consolidation.
This was an acute lobar pneumonia caused by Streptcoccus pneumoniae.
Based on the images alone, it is usually not possible to determine the cause of the consolidation.
Other things need to be considered, like acute or chronic illness, clinical data and other non-pulmonary findings.
Here we have a number of x-rays with consolidation.
Notice the similarity between these chest x-rays.
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