Prominent right atrial and superior vena caval shadow
Chest X-ray PA view showing prominent right atrial and superior vena caval shadow along with mild cardiomegaly. Right atrial enlargement (RA) is suggested by the rightward shift of right cardiac border. Superior vena caval (SVC) shadow can be traced upwards from the upper part of the right right atrial contour. Right bronchus (RB) can be seen as a more vertical air column than the left bronchus (LB) which is more horizontal. In general the vascular markings in the lung are a bit more prominent than usual. Main pulmonary artery segment is visible below the aortic knuckle as little bulge beyond the left cardiac border.
Aortic knuckle is considered as the first mogul and the pulmonary artery the second mogul on the left cardiac border. It the left atrial appendage is prominent, it becomes the third mogul sign (not seen here).