Postaortic left innominate vein: radiological assessment and pathogenesis.

Postaortic left innominate vein (PALIV) is a rare venous anomaly and the findings on plain chest radiographs have not been well described. Plain chest radiographs, CT and MR of nine adults known to have PALIV were reviewed. They all showed a high aortic arch, including four with a right-sided aortic arch and one with a double aortic arch, in postero-anterior radiographs, and seven showed curved shadows in the left upper mediastinum. On all lateral chest radiographs (n = 5), the superior retrosternal region was opacified by the high aortic arch. CT or MR images confirmed the aortic arch and/or innominate artery to be in that part of the retrosternal space, normally occupied by the left innominate vein, in all cases. Association of a curved shadow in the superior mediastinum with a high aortic arch on plain chest radiographs is therefore suggestive of, though not diagnostic for, PALIV. This entity was well documented by CT or MR and the radiological findings were considered to imply that developmentally PALIV is secondary to a high position of the aortic arch.