Lucency outlining the aortic arch on frontal view. Indicates Left upper lobe collapse. The lucency occurs as a result of the superior segment of the left lower lobe migrating superiorly and abutting the aortic knob due to volume loss of the left upper lobe.
A crescent of lucency surrounding the aortic knob on the frontal view. may be accompanied by findings of Left Upper Lobe Collapse.
- The Luftsichel Sign - DG Blankenbaker - Radiology 1998; 208: 319.
- Medcyclopaedia - Lobar Atelectasis