Luftsichel sign

What is the Luftsichel sign?

The “Luftsichel” (air sickle) sign represents a small curvilinear lucency that parallels the left upper mediastinum on a frontal chest radiograph. This occurs in the setting of left upper lobe atelectasis due to interposition of the superior segment of the left lower lobe between the medially displaced and collapsed left upper lobe and aortic arch.