Luftsichel Sign [PDF]
References:

1) Blankenbaker DG. The Luftsichel Sign. Radiology 1998;319-320 [PDF]

2) Isbell D, Grinnan D, Patel MR. Luftsichel Sign. The American Journal of Medicine 2002;112:676-677  [PDF]

3) Marshall GB, Farnquist BA, MacGregor JH. Signs in Thoracic Imaging. J Thorac Imaging 2006;21(1):76-90 [PDF]