Hilum Overlay Sign
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References:

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

2) Felson B. More Chest Roentgen Signs and How to Teach Them. Radiology 1968;90:429-441
[PDF]  

3) Felson B. The Mediastinum. Seminars in Roentgenology 1969;4(1):41-58
[PDF]