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