The Silhouette sign

When two objects of similar density lie close together, then their margins will not be visible on Film.  This sign will help us to give us information on  the location of the lesion. 

There is consolidation in the right middle and lower zone whose margins are not distinct from the right heart border ( silhouetting the right heart border), hence it is a case of Right middle lobe consolidation. ( this is because the right heart border lies adjacent to the right middle lobe) .

Here, in the first column , is a list of structures in the chest Xray. These areas in the chest Xray will be silhouetted if there is pathology in the areas of lungs which are mentioned in the second column.

Let’s take another example.

In this chest Xray, the left heart border is silhouetted ( not distinct from) the consolidation in the left middle and lower zone. Referring to the table provided above, we can say that this is a lingular segment consolidation.