Surgical anatomy
In most instances, it courses from the left, extending posterior to the aortic arch, and traversing from left-to-right anterior to the trachea, and antero-superior to the bifurcation of the pulmonary trunk, before crossing posterior to the ascending aorta to terminate in the superior caval vein (Figures 1A-1F, 2A-2B). Characteristic features have been identified in that, first, the superior caval vein is shorter than the normal case, and second, the azygous vein does not drain into the right brachiocephalic vein.37 Very rarely, the retroaortic vein can join the azygous vein before entering the superior caval vein.31 In two instances, the vein has been found to drain directly into the left atrium, with production of severe cyanosis.12,13
We encountered 6 descriptions of the duplication of the vein, the branches encircling the aorta, and one report of persistent left superior caval vein with duplication of the left brachiocephalic vein.17,31,43,45-47 In one of the cases, the anterior and thinner vein coursed above the aortic arch, anterior to left common carotid artery, and then passed between the left common carotid artery and brachiocephalic trunk to join the right superior caval vein. The posterior thicker retroaortic vein coursed posterior to trachea and esophagus and joined the azygous vein at the level of the second thoracic vertebra before draining to the right superior caval vein.31
Some investigators have recognized three variations in course relative to the arterial duct or its ligamentous remnant, with the vein either passing anteriorly or posteriorly, or passing behind one or more of the main aortic branches but retaining a normal relationship to the aortic arch .18,21 Another group, however, having assessed several series, argued in favour of four patients.17,19,38-42 They suggested that the vein could cross the midline above the aortic arch, but posterior to the origin of great arteries (Figures 5A and 5B). In their second pattern, the vein passes beneath the aortic arch, but above the bifurcation of the pulmonary trunk, passing in front of the arterial duct (Figure 5C). The third pattern was characterized by a course posterior to the arterial duct, with crossing the midline beneath the aortic arch and above the pulmonary arteries (Figure 5D). In the final pattern, the vein crosses the midline behind the pulmonary trunk away from the arterial duct (Figure 5E). It subsequently became possible to identify two more patterns. In the first of these, the vein takes a more posterior route relative to the trachea and esophagus, subsequently joining the azygous vein before draining to superior caval vein (Figure 5F).31 The sixth pattern is produced by duplication of the vein (Figure 5G).31,43 There is then additional variation in the setting of duplication. The anterior vein has been described as passing above the aortic arch and coursing anterior to the left common carotid artery and brachiocephalic arteries, before draining into the superior caval vein. The posterior vein runs below the aortic arch and courses posterior to the descending aorta. Both veins in this variant drain separately into the superior caval vein (Figure 5H).17,18,23,43-47
From the 250 reported cases we were able to identify, three-quarters with associated congenitally malformed hearts. Of these 189 patients, all but 7 had usual atrial arrangement. Right isomerism was reported in 5 patients, with two patients having left isomerism.4,12,13,23 Detailed description of the cardiac anomalies was provided for 145 patients.48,49Of these, almost two-thirds had tetralogy of Fallot, or its variants, with just over one-sixth having ventricular septal defects with pulmonary atresia.2,5,6,11,14,22,23,27-29,49-52 Over four-fifths had malformations involving the outflow tracts. Among these patients, two-thirds had a right aortic arch, with two patients having a cervical aortic arch, and one patient a double aortic arch.14,22,27-29,50-53 In those without congenital heart diseases, one-sixth had right aortic arch3,4,27, just under one-tenth had double aortic arches,27,28,53and two-fifths had cervical aortic arches.22,52,54,55