A Rare Case of Two Superior Vena Cava with Two Azygos Veins in a Cadaver

Abstract

In embryonic life developmental malformation of thoracic veins can lead to anomalies of the Superior vena cava and major thoracic veins like Azygos system. Double superior vena cava and double azygos vein are rare congenital anomaly with the incidence of 0.3%. These types of congenital anomalies may or may not be presented with clinical symptoms. This case was noted during the routine cadaveric dissection of thoracic region and heart for medical students in department of Anatomy, we found double superior vena cava (persistent left superior vena cava) along with double (paired) azygos vein in a female cadaver. Right superior vena was formed by the union of right subclavian and right internal jugular vein which receives the arch of right azygos before it opened into the right atrium. Left superior vena cava was formed by the union of left subclavian and left internal jugular vein and it also receives the arch of left azygos vein before it entered into the right atrium. In present case coronary sinus was separated from left persistent superior vena cava and it opened in the persistent left superior vena cava. There was no communication between both the superior vena cava. On right side Azygos vein was normal and open into right superior vena cava. On the left side hemiazygos was in continuation with the accessory azygos vein and it also forming the arch and opened into persistent left superior vena cava. There were no other congenital anomalies present in the heart. These types of congenital anomalies extremely very rare where the left superior vena cava opens into the right atrium directly and coronary sinus opens in to this left superior vena cava. Majority of such types of cases remain asymptomatic. Some cases may be detected accidently during diagnostic or surgical procedures like cardiac angiography, cardiac catheterization, by- pass and dialysis or during autopsy or institutional cadaveric dissection.

BACKGROUND

Developmental malformation of thoracic veins can lead to anomalies of the vena cava and major thoracic veins such as the azygos venous system. Due to faulty embryonic development, sometimes, the superior vena cava on the left side persists along with the physiological superior vena cava on the right side. Persistence of superior vena cava on the left side is a very rare congenital anomaly with 0.3% incidence.[¹] These types of anomalies may occur in association with malformations of the heart such as septal defect (atrial or ventricular) or other vascular anomalies such as anomalies in azygos veins.[²] Such types of congenital anomalies can cause problems during central venous invasive procedures or cardiac invasive procedures. Since this is a rare congenital anomaly, which was noted in a cadaver during routine dissection, the case report will add some value in the scientific domain for the researchers.

In this article we report a case of the presence of superior vena cava on both sides, along with two azygos veins in a cadaver and discuss its embryological basis and review the literature with reference to it.

CASE REPORT

This case was noted during the routine dissection of a female cadaver, age 60 years, with no significant history of any cardiovascular disease, in the department of anatomy in 2022. Gross dissection was performed of the thoracic region (mediastinum). Morphology of the heart and both superior vena cava (right and left) along with both azygos veins (right and left) was observed. Morphometry (length and width) of both the superior vena cava and the orifice of the superior vena cava of the left side were done by digital vernier caliper (mm). IEC approval was taken for the case report (Ref. No. IEC/RMCH/86/2022/AUG).

In the cadaver, we observed superior vena cava on both sides (right and left) and double (paired) azygos vein. The right subclavian and internal jugular vein unites to form the superior vena cava on the right side, which received the arch of azygos (right) before draining into the right atrium. Its circumference was 26.21 mm and its length was 95 mm.

Similarly, on the left side, we observed the left subclavian and left internal jugular veins unite to form the superior vena cava on the left side which receives the arch of the azygos vein (left). This left superior vena cava passed lateral to the aortic arch and then between pulmonary veins of the left side and auricle and then entered into the left posterior coronary sulcus. [Figure 1] This left superior vena cava was draining in the right atrium, and its opening was situated between the orifice of the inferior vena cava and the atrioventricular orifice [Figure 2]. Its circumference and length were 36.8 mm and 160 mm, respectively. Measurement of the left superior vena cava orifice was 30 mm × 20 mm.

Figure 1: Posterior view of the heart showing persistent left superior vena cava with the arch of left azygos and separate coronary sinus. SVC: Superior vena cava, PLSVC: Persistent left superior vena cava

Figure 2: Interior of right atrium showing the opening of PLSVC. PLSVC: Persistent left superior vena cava, IVC: Inferior vena cava

Coronary sinus was also present in the left coronary sulcus which runs separately [Figure 1]. Opening of coronary sinus was present within the wall of the left superior vena cava [Figure 3]. For confirmation, we cut the lumen of the left superior vena cava along its long axis and we observe that the opening of the coronary sinus was present within the wall of the left superior vena cava. There was a common wall which separates the coronary sinus and superior vena cava (left). The length of the coronary sinus was 86 mm and the circumference was 23 mm. Measurement of opening of the coronary sinus was 5 mm × 5 mm [Figure 4]. There was no communication between both superior vena cava.

Figure 3: Interior of right atrium showing the opening of coronary sinus within the wall of Persistent left superior vena cava near its opening into the right atrium. CS: Coronary sinus

Figure 4: Interior of left superior vena cava showing the opening of coronary sinus (after cutting the wall of PLSVC, longitudinally). PLSVC: Persistent left superior vena cava, CS: Coronary sinus

Azygos vein on the right side was normal and open into the superior vena cava (right) [Figures 1 and 5]. On the left side, the formation of hemiazygos vein was normal (by the union of left subcostal vein and ascending lumber vein) and received an accessory azygos vein, before forming the arch. This arch of the left azygos vein crosses the arch of the aorta laterally and arched over the left lung root and opened into the superior vena cava of the left side at the sixth thoracic vertebral level. There was no communication between the two azygos veins [Figures 1 and 6]. Posterior intercostal veins of 2^nd, 3^rd, and 4^th space open into respective azygos veins. The caliber of both the azygos veins was normal and almost similar. There were no other congenital anomalies present in the heart or other venous anomalies in the azygos and vena cava system in the thorax as well as in the abdomen.

Figure 5: Right thoracic cavity showing right azygos vein along with the part of the arch of azygos vein (after removing the lungs and heart)

Figure 6: Left thoracic cavity showing left azygos vein with its arch (after removing the lung and heart)

EMBRYONIC CONSIDERATION

At 4^th week of intrauterine life, three paired veins enter into the venous end of the heart tube of the embryo. Three veins are vitelline veins, umbilical vein, and common cardinal vein draining the yolk sac, chorionic blood, and the blood from the body of the embryo, respectively. Hence, the main draining channel of blood from developing embryos is through cardinal veins which eventually take part in the formation of the vena cava system. There are two cardinal veins, anterior and posterior which drain the cranial and caudal parts of the embryo, respectively. Common cardinal vein is formed by the union of anterior and posterior cardinal veins on both sides, which eventually drain into the respective horn of sinus venosus of the heart tube. During the development of the venous system, there is the formation of shunts between the veins of the left and right side so that blood from these veins is channeled to the right side. Later at 8^th week of intrauterine life, a connecting channel develops which connects both anterior cardinal veins to shunt the venous blood from left to right side. Later on, brachiocephalic vein of the left side formed by this connecting channel and the left anterior cardinal vein caudal to this channel regresses. On the right side, the superior vena cava develops from the right anterior and common cardinal vein, the right posterior cardinal vein later on regresses but some parts form the root of the azygos vein. Sometimes, the left anterior cardinal vein caudal to anastomosing channel fails to regress and forms the superior vena cava on the left side. This anastomosing channel may or may not be present.[³] This superior vena cava of the left side generally drains into the coronary sinus, as the embryologic connection of the left common cardinal vein and the left horn of the sinus venosus, because coronary sinus develops from the left horn of sinus venosus.

In the present case, there was no connection between both the superior vena cava, it suggested that there was no anastomosing channel present between the right and left anterior cardinal veins during development. Hence, we consider that in the present case, the superior vena cava of the left side derived from persistent left anterior and common cardinal vein which opened into the right atrium. However, in the present case, there is a unique presentation in that it is not draining through the coronary sinus. In fact, it is separated from the coronary sinus and the coronary sinus opens into it. This is an unusual finding.

During 5^th–8^th week of intrauterine life, additional veins start developing such as subcardinal veins (drains kidney), sacrocardinal vein (drains lower extremities), and supracardinal veins (drains body wall), which drain in posterior cardinal veins. Gradually with the regression of posterior cardinal veins, the body wall is mainly drained by supracardinal veins. Right intercostal veins from the right 4^th to 11^th intercostal space drain into right supracardinal vein. Azygos vein is formed by the right supracardinal vein and part of the posterior cardinal vein (arch of azygos). Left posterior intercostal veins from 4^th to 11^th intercostal space drain into the left supracardinal vein (hemiazygos vein). Hemiazygos vein through the anastomosing channel, shunting the blood flow from left to right side into the azygos vein (right). Left superior intercostal vein is formed by the terminal part of the posterior cardinal vein (which enters in brachiocephalic vein of left side).[⁴]

In the present case, there were two azygos veins, one on right and one on left side. Both were opening into respective superior vena cava through forming the arch. This may be because the persistence of the left side cardinal venous system and left azygos venous line which derives from the left supracardinal vein. There was no communication between two azygos veins also just like there was no communicating channel between two superior vena cava in the present case. Hence, in the present case, both right and left vena caval system and the azygos system are mirror image and with no communication in between, but both the superior vena cava opens into the right atrium and also no congenital defect was present in the right atrium or other chambers of the heart. Hence, there was no right-to-left shunting. In the present case, the explanation for the separate opening of the persistent left superior vena cava into the right atrium (not through coronary sinus) could be a duplication of the left horn of sinus venosus. It is an exceptionally very rare anomaly and could not be found in any literature.

DISCUSSION

Varieties of cases of congenital anomalies of the thoracic venous system were reported either during routine cadaveric dissection or during some radiological interventional procedures. Nandy and Blair observed two superior vena cava with symmetrical two azygos veins in 45 years Caucasian male cadaver during routine dissection. In this, the superior vena cava of the left side drains into the coronary sinus, whereas in the present case, it drains directly in the right atrium.[⁵]

In Chinese cadaver, Liu et al. observed a superior vena cava on the left side with hemiazygos vein which continued with accessory hemiazygos vein and drained into the superior vena cava of the left side and this drained in dilated coronary sinus then in the right atrium.[⁶]

Iimura et al. observed superior vena cava on both sides along with right and left azygos with the right-to-left shunt in Japanese male cadavers. They reported that the upper edge of the interatrial septum was present at the orifice of the superior vena cava (right-to-left shunt). Communications were present between two azygos veins, and the left azygos vein was thinner than the right.[⁷] In the present case, there was no right-to-left shunt, no communication between two azygos and the caliber of both the azygos veins was almost similar.

In Japanese cadaver, during dissection, Ogami-Takamura et al. found that the superior vena cava was present on both the side with the connecting channel between them along with the opening of two thymic veins in it and the superior vena cava of the left side was draining in the coronary sinus.[⁸]

Tyrak et al. observed in the cadaver that there were two superior vena cava. Orifice of the superior vena cava of the right was small. On the left side, they found common trunk formed by both superior and inferior pulmonary veins. On the right side, an additional middle pulmonary was present along with separate superior and inferior pulmonary vein open into left atrium.[⁹]

Aragão et al. dissected 30 weeks male fetus and reported two superior vena cava. On the left side, it drained in the left atrium along with pulmonary veins.[¹⁰]

During cadaveric dissection, Mittal et al. observed two superior vena cava (right and left). Superior vena cava of the left side was draining in the coronary sinus.[¹¹]

Clinical implication

Majority of such types of cases remain asymptomatic. Some cases may be detected accidently during diagnostic or surgical procedures such as cardiac angiography, cardiac catheterization, and bypass and dialysis. These types of anomalies produce symptoms when they are associated with the right-to-left shunt.[^3,4] In the present case, there is no right-to-left shunt and the superior vena cava of the left side directly opens in the right atrium, not in the coronary sinus. Hence, these types of anomalies are clinically relevant for cardiovascular surgical and diagnostic procedures.

CONCLUSION

Various developmental anomalies of thoracic veins remain asymptomatic until they are presented with other developmental malformations of the heart and other structures which causing right-to-left shunt. These types of anomalies, without the right-to-left shunt, may be encountered during other diagnostic or interventional cardiovascular procedures or during cadaveric dissection or autopsy[^{5,6,7,8,9,10,11}] because they are usually asymptomatic. The present case is a unique case because in this case superior vena cava of the left side individually drains into the right atrium. The coronary sinus was separated from this by a common wall, and it opened in the wall of the left superior vena cava.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Acknowledgment

1. We would like to thank Dr. Priya Rani Adhaya (BDS), MSc 2^nd year student helping in the dissection and preserving the specimen
2. Mr. Sunil, Laboratory assistant for his support and for preserving the specimen.

The authors also sincerely thank those who donated their bodies to science so that anatomical research could be performed. Results from such research can potentially increase mankind's overall knowledge which can then improve patient care. Therefore, these donors and their families deserve our highest gratitude.[¹²]