Calcification of the intima of aortic knuckle (arrow) is a common finding in the elderly. Usually it is of no significance. But a separation of the intimal calcification from the edge of the aortic knuckle shadow indicates a separation of the intima from the media as in aortic dissection. This has been called the “calcium sign” in aortic dissection. A separation of more than 1 cm is considered significant.
LPA: left pulmonary artery; RPA: right pulmonary artery