Figure 2. Volume-rendered, coloured 3D reformat images of the CTA using opacity threshold for segmentation. (A) Image showing arterial supply originating from the descending thoracic aorta (arrowhead). The proximal segment is tortuous with aneurysm formation at its mid-segment (asterix). The distal branches have a normal caliber, with gradual tapering. (B) The left inferior pulmonary vein (V) commences below the aneurysm sac, then courses anteromedially before joining with the left superior pulmonary vein to drain into the left atrium. There is no direct communication between these veins and the systemic artery. (C) The pulmonary arteries have been included, showing paucity of branches to the left lower lobe, which is supplied by the aberrant systemic artery. CTA with curved coronal reformats. (D) Image in the pulmonary angiographic phase shows a gracile left lower-lobe pulmonary artery coursing alongside the lower-lobe bronchus before terminating early. There is no communication with the aberrant arterial supply and no opacification of the aneurysm sac. (E) Image showing continuation of the tracheobronchial tree into the left lower lobe. (F) Mild scarring and bronchiectasis with areas of atelectasis at the left lung base were attributed to compression of the lower-lobe segmental bronchi by the aneurysm (arrows).