YouTube lecture: Please pay attention to the broadening carinal angle and the stag's antler sign.
The stag's antler sign refers to upper lobe pulmonary venous diversion (cephalization) in pulmonary venous hypertension or pulmonary edema as seen on frontal chest radiograph. The prominence of upper lobe pulmonary veins resemble stag's antler. It is the earliest sign of pulmonary venous hypertension (grade 1 pulmonary edema). This sign is also known as hands-up sign or inverted moustache sign.