This is a very important sign. It enables us to find subtle pathology and to locate it within the chest.
The loss of the normal silhouette of a structure is called the silhouette sign.
Here an example to explain the silhouette sign:
The heart is located anteriorly in the chest and it is bordered by the lingula of the left lung.
The difference in density between the heart and the air in the lung enables us to see the silhouette of the left ventricle.
When there is something in the lingula with the same 'water density' as the heart, the normal silhouette will be lost
When there is a pneumonia in the left lower lobe, which is located more posteriorly in the chest, the left ventricle will
(still be bordered by air in the lingula and we will still see the silhouette of the heart (red arrow
The PA-film shows a silhouette sign of the left heart border.
Even without looking at the lateral film, we know, that the pathology must be located anteriorly in the left lung.
This was a consolidation due to a pneumonia caused by Sterptococcus pneumoniae.
There are some areas that need special attention, because pathology in these areas can easily be overlooked:
zone below the dome of diaphragm
These areas are also known as the hidden areas.
Notice that there is quite some lung volume below the dome of the diaphragm, which will need your attention
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