Because of a Valsalva manoeuvre during the image acquisition, contrast has refluxed in the venous circulation, causing particularly prominent opacification of a vein connecting the accessory hemiazygos vein to the left brachiocephalic vein. This vein is the left superior intercostal vein, which gives the radiographic image of an "aortic nipple". The azygos vein is not seen except in its arch, most likely hypoplastic with compensatory enlargement of the hemiazygos drainage system.