Silhouette sign
ChestRadiograph
Loss of a normally visible border between two structures of similar radiographic density that lie in direct contact.
What it means
The opacity abuts a specific structure, allowing anatomical localisation of the disease.
Mechanism
Two soft-tissue densities in contact share the same attenuation, so their interface disappears; an intervening air-filled lung would preserve it.
Associated conditions
- Right middle lobe consolidation (right heart border)
- Lingular consolidation (left heart border)
- Lower lobe consolidation (diaphragm)
- Anterior mediastinal mass
Pearls
- Loss of the right heart border localises disease to the right middle lobe.
- A preserved border means the opacity is not in contact with that structure.
References
- Radiopaedia: Silhouette sign
For educational use only. This dictionary is a study aid and reference, not a diagnostic tool, and must not be used to guide clinical decisions or patient care. Imaging appearances vary; always correlate with the full clinical picture and confirm with a qualified radiologist.