Silhouette Sign

When examining the lung fields of a normal CXR, the silhouettes of the heart borders, the ascending and descending aorta, the aortic knob and the hemidiaphragms should be clear. Obliteration of any of these silhouettes by a water density can be caused by infection in the lung, blood, pus, etc and is known as the ‘silhouette sign’. All of these silhouettes, or structures, are in contact with a specific portion of the lung. Therefore, by determining exactly which structure is obliterated, you can determine where the lung pathology is located.

Silhouette/Structure
Contact with Lung
Upper right heart border/ascending aorta
Anterior segment of RUL
Right heart border
RML (medial)
Upper left heart border
Anterior segment of LUL
Left heart border
Lingula (anterior)
Aortic knob
Apical portion of LUL (posterior)
Anterior hemidiaphragms
Lower lobes (anterior)

**Remember! Anterior left hemidiaphragm is normally obliterated by the heart


Sihouette Sign #1: 45 y/o male with cough, fever and pleuritic chest pain

Sihouette Sign #2: 30 y/o female with fever of unknown origin

Umm...where is the Silhouette Sign?: 15 y/o girl with cough and fever

 

Air Bronchogram Sign

 

5 Abnormalities

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