On a plain chest radiograph, the 'silhouette sign' is used to localise intrathoracic pathology. A right lower lobe consolidation would obliterate which border?
- A Right cardiac border
- B Right hemidiaphragm ✓
- C Right hilum
- D Aortic knuckle
Correct answer: B. Right hemidiaphragm
Explanation
The silhouette sign states that two structures of the same radiodensity in contact will efface each other's border. The right lower lobe lies against and shares a border with the right hemidiaphragm; consolidation here obliterates the diaphragmatic border. Right middle lobe consolidation obliterates the right heart border. The aortic knuckle is obliterated by left upper lobe lesions. The hilum is a distinct structure not defined by the silhouette sign in the same way.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.