The x-rays show a ‘sail sign’ – like the triangular sail of a yacht.
Image 1 shows a thymic sail sign. This is a normal finding in infants and children up to 2 years of age and may sometimes also be seen in an older child. There is a triangular density adjacent to the right superior mediastinum with the base abutting the horizontal fissure.
The thymic sail sign can be mistaken for a right upper lobe consolidation, especially if the x-ray is rotated.
Image 2 shows a sail sign related to left lower lobe collapse. There is a triangular density behind the heart, causing a double left heart border.
Image 3 shows a sail sign related to elevated anterior elbow fat pad. There is an associated fracture of the olecranon.
Reference: Fundamentals of Diagnostic Radiology by Brant and Helms.