Figure 2. (a) Axial T₁ weighted spin-echo image shows a "four artery sign", which comprises the anterior common carotid (large black arrows) and posterior subclavian (small black arrows) arteries in the symmetrical position. Moreover, the small left arch (small white arrow) transforms into an aneurysm (large white arrow) via the narrow lumen. (T, trachea; E, oesophagus). (b) Axial T₁ weighted spin-echo image 2.5 cm inferior to (a) demonstrates proximal right aortic arch (RA) with a retro-oesophageal segment, anterior common carotid arteries (large black arrows), posterior right superior vena cava (large white arrow) and posteroinferior distal aortic arch (small black arrow). The proximal and middle aortic arch compresses the right lateral and posterior wall of the trachea (T) with resultant narrowing of the lumen. Displaced azygos vein (large white arrow), which separates the azygos lobe from right upper lobe, drains into the superior vena cava. Double white arrows show the position of the oesophagus.