In radiology

Radiology

Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...

, the silhouette sign refers to loss of normal border between structures,, or an intra-thoracic radio-opacity obscuring the border of the heart

Heart

The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 or aorta

Aorta

The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...

 due to a contiguous structure. 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 come up as white on a standard X-ray. It may occur, for example, in middle lobe disease, where the right heart margin is lost, and in right lower lobe pneumonia

Pneumonia

Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

, where the border of the diaphragm on the right side is obscured, while the right heart margin remains distinct.

External links

• The Silhouette Sign Revisited, Vernon J. Louw, Adrian Schmidt, Chris T. Bolliger. Lung Unit, Department of Internal Medicine, Tygerberg Hospital, Cape Town, South Africa.
• The silhouette sign and possible mechanisms, Ian Maddison Nov 1994, revised Nov. 2007.
• Silhouette Sign