Silhouette Signs
Look For
- Obliteration of normally clear outlines between the lung fields and adjacent structures such as the heart, aorta or hemidiaphragm.
Significance
- Loss of normal borders appears when the adjacent area of lung is consolidated or collapsed.
Interpretation
- Upper right heart border / ascending aorta - anterior right upper lobe
- Upper left heart border - anterior left upper lobe
- Aortic knob / arch - apical left upper lobe
- Right heart border - right middle lobe
- Left heart border - lingular lobe
- Anterior hemidiaphragms - lung bases / lower lobes
Examples
- Obscuration of the right hemidiaphragm suggesting right lower lobe consolidation
![Obscuration of the right hemidiaphragm suggesting right lower lobe consolidation]()
- Obscuration of the left hemidiaphragm suggesting right lower lobe consolidation
![Obscuration of the left hemidiaphragm suggesting right lower lobe consolidation]()
- Obscuration of the ascending aorta, suggesting right upper lobe consolidation
![Obscuration of the ascending aorta, suggesting right upper lobe consolidation]()
Mediastinal Air
Air within the mediastinum is known as pneumomediastinum.
Look For
- Overly sharp mediastinal borders
- Lucencies around the cardiac apex and great vessels
Example
- Pneumomediastinum and pneumoperitoneum in a post-trauma patient
![Pneumomediastinum and pneumoperitoneum in a post-trauma patient]()
Causes of Pneumomediastinum
- Tracheal / major bronchial rupture - trauma, iatrogenic, spontaneous
- Oesophageal rupture - trauma, iatrogenic, spontaneous
- Alveolar rupture - asthma, airway foreign body, mechanical ventilation, coughing, vomiting, pneumonitis, emphysema, fibrosis
- Tracking of air from the neck - facial fracture, dental extraction, tracheostomy
- Tracking of air from the abdomen - hollow viscous perforation
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