Discussion

It is worth noting that the word “Heterotaxia” implies an alteration in the asymmetry of thoracic-abdominal organs. Hence, it denotes no more than an abnormal arrangement and includes mirror-imagery. The arrangement in the heart is frequently described as “atrial isomerism.” This is also incorrect. Within the heart, it is only the atrial appendages that can be isomeric. ^{Reference Tremblay, Loomba and Frommelt1–Reference Anderson, Becker and Freedom3,Reference Uemura, Ho, Devine, Kilpatrick and Anderson5–Reference Loomba, Ahmed, Spicer, Backer and Anderson7} In our case, characterised by two atrial chambers with each having atrial appendages of left morphology, as expected there was also left isomerism of the lungs and bronchial tree. When such cases are found with mixed atrioventricular connections, the atrioventricular junction itself is usually guarded by a atrioventricular common valve. ^{Reference Tremblay, Loomba and Frommelt1–Reference Anderson, Becker and Freedom3} Our case was particularly unusual in that, despite the presence of two separate atrioventricular valves, the right-sided valve was imperforate.

In the study of Tremblay et al, ^{Reference Tremblay, Loomba and Frommelt1} of 57 cases of left isomerism, 44 cases had the superior caval vein connected to the right-side atrium, and 8 cases had the inferior caval vein (without interruption) connected to the same atrium. In 20 cases, the suprahepatic veins drained into the inferior caval vein, while 40 cases presented a coronary sinus. With respect to the pulmonary venous return, three cases with quasi normal arrangement were reported. The five aspects (above commented) of the systemic and pulmonary venous return reported by Tremblay et al ^{Reference Tremblay, Loomba and Frommelt1} were present in our case. With regard to atrioventricular junctions, they reported 34 hearts with two atrioventricular orifices (but none with an imperforate atrioventricular valve) and 50 hearts with atrioventricular mixed connections as it was found in our case. In relation to ventriculo-arterial connections¸ they found 33 cases with concordant ventriculo-arterial conections, a situation which was also found in our case. However, they did not report any case with overriding of some great artery as in the present case. Moreover, in their study, they did not report any case with vascular ring, which differs from the present case, where this malformation was found.

In addition, an imperforate tricuspid valve (membranous atresia), in the setting of biventricular atrioventricular connections, is not the “classical” form of tricuspid atresia; rather, it is a quite rare variant. The usual variant is the absence of the right atrioventricular connection. This point is one of the various interesting aspects of this case, and this rare variant had never been described in the set of left isomerism.

The vascular rings are pathologies of embryological origin in the development of the aortic arches. The development of these arches is regulated by neural crests and represents less than 1% of all cardiovascular anomalies. ^{Reference de Pedro, Martínez Ayúcar, Marín Gonzalo, Galdeano Miranda and Luis García8}

In 1737, Hommel described the anatomy of a vascular ring in a postmortem case, where he reported the presence of double aortic arch. ^{Reference de Pedro, Martínez Ayúcar, Marín Gonzalo, Galdeano Miranda and Luis García8} It was not until 1945 that the term “vascular ring” was coined by Robert H. Gross. ^{Reference de Pedro, Martínez Ayúcar, Marín Gonzalo, Galdeano Miranda and Luis García8} The vascular rings are not usually associated with other CHD. However, Sánchez et al ^{Reference Sánchez, Rey and Polo9} reported other associated congenital heart malformations in 19.2% of their cases with vascular rings. In addition, other malformations of the digestive tract, such as oesophageal atresia and urinary malformations like hypospadias, have also been described. ^{Reference Sánchez, Rey and Polo9}

In the present case, the vascular ring has (at the right side) a vessel with a very atypical loop that bears a duct at the left side. Thus, this atypical vessel continues with the left descending aorta forming a semicircle (from anterior to posterior) with a different size as the ascending and descending aorta.

The vascular rings are best explained on the basis of the hypothetical double arch as was put forward by Edwards and colleagues. ^{Reference Edwards10} The present case may be explained on this basis (but it is not the only possible explication). The double arch is interrupted on the left side between the left common carotid artery and the left subclavian artery, but the ring is completed by the left-sided duct. The right “arch” is somewhat elongated, which gives rise to the right common carotid and right subclavian arteries, but the possibility that a right “duct” or a right “abnormal” vessel is feasible; this “arch” or “duct” then continues in retro-oesophageal fashion to supply the left subclavian artery and a left-sided duct. Maybe, we will never know the right explanation about the morphogenesis in this atypical vascular ring encountered in our patient.

It is of note that this vascular ring is very loose around the tracheal-oesophageal pedicle and also all supra-aortic vessels emerge separately, very far from each other.