From Wikipedia, the free encyclopedia
Radiologic sign
Medical condition
Silhouette sign
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A) Normal chest radiograph; B) Q fever pneumonia affecting the right lower and middle lobes. Note the loss of the normal radiographic silhouette (contour) between the affected lung and its right heart border as well as between the affected lung and its right diaphragm border. This phenomenon is called the
silhouette sign
|
Differential diagnosis
| right middle lobe syndrome
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In
radiology
, the
silhouette sign
refers to the loss of normal borders between
thoracic structures
.
[1]
It is usually caused by an
intrathoracic
radiopaque mass
that touches the border of the
heart
or
aorta
.
[2]
In other words, it is difficult to make out the borders of a particular structure - normal or otherwise - because it is next to another dense structure, both of which will appear white on a standard
X-ray
.
[3]
It may occur, for example, in
right middle lobe syndrome
, where the right heart margin is obscured, and in
right lower lobe
pneumonia
, where the border of the
diaphragm
on the right side is obscured, while the right heart margin remains distinct.
[2]
Silhouette sign is very useful in localizing lung lesions as all structures forming cardiac silhouette are in contact with a specific portion of the lung.
References
[
edit
]
Further reading
[
edit
]
- The Silhouette Sign Revisited
, Vernon J. Louw, Adrian Schmidt, Chris T. Bolliger. Lung Unit, Department of Internal Medicine, Tygerberg Hospital, Cape Town, South Africa.