By Dr Deepu
Silhouette sign/loss of silhouette sign/ loss of
outline sign.
I was always confused with the silhouette sign for
its hidden meaning and failure to decode it by many medical students. So, I
thought it would be apt to unravel it so that it could be handy for many
medical students.
One of the most useful signs in chest radiology is
the silhouette sign. This sign was described by Dr. Ben Felson. The silhouette
sign is in nothing but elimination of
the silhouette or loss of lung/soft tissue interface caused by a mass or fluid
in the normally air filled lung. For instance, if an intrathoracic opacity is
in anatomic contact with, for example, the heart border, then the opacity will
obscure that border. The sign is commonly applied to the heart, aorta, chest
wall, and diaphragm. The location of this abnormality can help to determine the
location anatomically.
Just go through the X Ray to know the various structures seen in the chest x ray.
Let me explain this with this image.
What do we see???
There is plastic bottle which is surrounded by air,
the margins of the shadow is very well
demarcated from the surrounding air.
First scenario: There are two bottles, made of same
material, placed apart from each other. The shadows appears separate from each
other. Let us consider the right bottle to be the heart and the air surrounding
the bottle as lung. The left bottle as a mass, since they are far from each
other, the border of both is visible
clearly.
Second scenario: Here we see the bottles are
touching each other at two points and there is no gap in between and if we look
at the shadow, we cannot differentiate between the two shadows, they appear
like a single opacity at the upper and lower ends.
For the heart, the silhouette sign can be caused by
an opacity in the RML, lingula, anterior segment of the upper lobe, lower
aspect of the oblique fissure, anterior mediastinum, and anterior portion of
the pleural cavity.
This
contrasts with an opacity in the posterior pleural cavity, posterior
mediastinum, of lower lobes which cause an overlap and not an obliteration of
the heart border. Therefore both the presence and absence of this sign is
useful in the localization of pathology.
want to read more in chest radiology??? Have a look at the following pages
Chest Radiology
Signs in Chest Radiology
want to read more in chest radiology??? Have a look at the following pages
Chest Radiology
Signs in Chest Radiology