“Aorta-in-Aorta”Sign on Chest Radiograph Representing Enlarged Left Superior Intercostal and Hemiazygos Veins

erally from the aortic arch. Enlargement of the nipple is usually due to dilation of the left superior intercostal vein as it heads for the left innominate vein lateral to the aortic arch. Where the superior vena cava or, occasionally, the inferior vena cava-is obstructed, the aortic nipple becomes prominent and enlarged (1-4); according to Friedman et al. (1), a nipple larger than 4.5 mm in diameter is abnormal. Where they are dilated posterolateral to the descending thoracic aorta, the hemiazygos and accessory hemiazygos veins may lead to a new interface adjacent to the descending thoracic aortic interface (5). We recently encountered a patient with membranous obstruction of the inferior vena cava in whom the left superior intercostal and hemiazygos veins were dilated. At chest radiography, this simulated the presence of a second aortic knob and descending thoracic aorta lateral to the originals, and an “aorta-in-aorta”appearance was thus created. Case Report