Study of anatomical variations in the azygous venous system in human cadavers

Hemiazygos vein and Accessory hemiazygos vein lie on the left side in the posterior mediastinum of thorax and are the counterpart of azygos vein on right side. During routine cadaveric dissection of thoracic region in an adult male, we found an abnormal venous channel which was single and was lying on the left side of the vertebral column. It received tributaries from superior intercostal vein and posterior intercostal veins. We found this abnormal venous channel draining directly into left brachiocephalic vein in contrast to its usual drainage into azygos vein. Hence this can be considered as abnormal venous channel and variant of hemiazygos vein and accessory hemiazygos vein. The azygos and hemiazygos venous system is commonly encountered during surgical intervention performed on posterior thoracic wall. This case report provides a new data of potential clinical significance.

Though the azygos system is an important anastomotic channel between the superior and inferior venae cavae, little attention has been paid to it and to its intimate relation to the paravertebral veins. The arch of the azygos vein is often seen on the postero-anterior film of the chest and, according to Burke (2), was described by Nuvoli on frontal tomograms. Fleischner (5) mentioned its dilatation in congestive failure and Ellis (4) discussed possible confusion with more significant shadows. Stauffer (10) succeeded in catheterizing the azygos vein in 1951, and in the same year Mellins (9) showed free communication between the femoral and azygos veins when contrast material was injected through a catheter in the saphenous vein. Lessmann (7, 8) and Tori (12) give credit for successful intraosseous venography to Erhardt and Kneip in 1943. Drasnar (3) in 1946 reported on infusions and transfusions by way of the bone marrow and stated that he had performed intraosseous venography in 1942. Lessmann's work included intracostal venography. Tori (12) and Süsse (11) wrote exclusively on azygos opacification. The former injected the thoracic spinous processes, a technic which clearly showed the communication between the paravertebral and azygos systems, though in our hands it met with inconsistent results. Süsse reported on intracostal injection and mentions that Fischgold and Prospenzi had used thoracic spinous processes and Prospenzi and Ficara had also injected ribs. Other papers on this subject, appearing in the foreign literature, are not readily available. The azygos vein begins adjacent to the first or second lumbar vertebra as a continuation of the ascending lumbar vein. It enters the thorax through the aortic hiatus and arches forward at the fourth thoracic vertebra, over the root of the right lung, to enter the superior vena cava. On its right, it receives the subcostal and intercostal veins, the upper three or four of the intercostal veins draining by a common trunk, the superior intercostal vein. The left intercostals communicate with the azygos via the accessory hemiazygos and hemiazygos veins. The hemiazygos, the thoracic continuation of the left ascending lumbar vein, receives the lower four or five intercostal veins, and empties into the azygos at the level of T-9. The accessory hemiazygos is made up by the confluence of intercostal veins between T-3 and T-9. It drains into the azygos or hemiazygos at T-8. This anatomical description is taken from Gray (6) and corresponds to that of other texts. It appears to be stylized. We have not consistently produced opacification of the accessory hemiazygos and hemiazygos and have shown intercostal veins that are supposed to communicate with the hemiazygos draining directly into the azygos. In addition, the thoracic portion of the azygos often appears to be much further to the left than has been indicated (Fig. 1).

Introduction: Azygous venous system is the system of unpaired veins comprising of the azygous vein, the hemiazygous vein and accessory hemiazygous vein1. They are para vertebral in position, provided with valves and drain most of the blood from the thoracic and posterior abdominal walls. They communicate with the venacaval system infront and vertebral plexus behind. It connects the superior vena cava with the inferior vena cava. The azygous vein is inconstant in the mode of origin. Aim: To explore the anatomical variations in the course of azygous system of veins. Material and methods: The present study was done in the Department of Anatomy, Apollo institute of Medical sciences and Research, Hyderabad over a period of 2 years. The present study was conducted on 12 cadavers (irrespective of age and sex). The course of the azygos venous system in these 12 cadavers was carefully observed and documented. Results: Anatomical variation was found in two cadavers. Discussion: The azygous system of veins arises from a pair of longitudinal venous lines called right and left azygous venous lines on each side of the aorta1. On each side of the azygous venous lines lies two parallel primitive lines called right and left sub cardinal and posterior cardinal veins. It forms an important route for collateral circulation in venacaval occlusion such as in portal hypertension. It serves as the main collateral channel to shunt the blood from the upper half of the body to the inferior venacaval in case of superior vena caval obstruction. Conclusion: Identification and understanding of these variations are important during preoperative radiological investigations and surgical procedures especially spinal surgery between T7 and T12 to avoid injury which may lead to postoperative haematomas Keywords: Azygous venous system, azygous vein, venacaval system.

Malposition of a dialysis catheter in the accessory hemiazygos vein.

Multiple variations of the azygos venous system were detected during routine dissection. The hemiazygos vein was underdeveloped. On the left side of the thorax, posterior intercostal veins between the 8th and 11th intercostal spaces and the subcostal vein drained into the azygos vein independently. In addition, the posterior 4th, 5th, 6th and 7th intercostal veins united and formed two superior and inferior trunks. The superior common trunk, at the level of the T4 vertebra, crossed the vertebral column obliquely, lying anterior to the aorta and posterior to the esophagus, opening into the azygos vein at the level of the T4 vertebra. The other structures in this part were normal. There were different courses of the azygos vein system. This variation is important in mediastinal surgery and also in the interpretation of radiographs.

Background: The azygos system includes those veins which are straight in course, paravertebral in positionand not accompanied with the corresponding arteries. The azygos vein may arise as lumbar azygos veinfrom the back of inferior vena cava or by the union of right subcostal and right ascending lumbar veins. Itenters the thorax, receives lower 8 right posterior intercostal veins, superior intercostal vein, hemiazygosand accessory hemiazygos veins and ends by joining the superior vena cava. The hemiazygos vein is formedon the left in a manner similar to that of azygos vein. The aim of the present study was to investigate thevarious patterns of the azygos venous system.Methods: A total number of 30 cadavers were studied and were evaluated based on the study of Anson BJand Mcvay CB.Conclusion: Out of 30 specimens studied, 17 (56%) specimens showed normal pattern, 5 (16%) specimensshowed caterpillar pattern and rest 8 (26%) specimens showed ladder pattern.Azygos system of veins serve as an alternative drainage channel between superior vena cava and inferiorvena cava in case of obstruction. The knowledge of various patterns could be useful for radiologists andsurgeons to prevent intra-operative hazards.

Knowledge of variations of azygos and hemiazygos veins is of importance to cardiothoracic surgeons and radiologists during various surgical, radiological, and echography techniques. We report some unique variations of azygos system of veins observed during dissection classes for undergraduate medical students. The azygos vein was formed as usual by the union of right subcostal and ascending lumbar veins. The vein ascended upward and to the left to reach the midline at the level of the 9th thoracic vertebra. After ascending till 5th thoracic vertebra, it gradually inclined to the right of midline and terminated by opening into the superior vena cava at the level of the 3rd thoracic vertebra. There was no major variation in the tributaries of the azygos vein on the right side, except that the right superior intercostal vein crossed behind the azygos vein from right to left and opened into the left side of the azygos vein. Further, two anastomotic veins connected the 10th, 11th and 12th posterior intercostal veins with each other to form two anastomotic circles on the right side of 10th to 12th thoracic vertebrae. The hemiazygos vein bifurcated on the left side of the 10th thoracic vertebra and the two ends opened into the azygos vein at the level of 9th and 10th thoracic vertebrae forming a venous circle in front of the 10th thoracic vertebra. The course of accessory hemiazygos vein was noteworthy. Instead of its classic descending course, the vein ascended upward from the left side of the 8th thoracic vertebra till the 6th thoracic vertebra before opening into the azygos vein.

BackgroundThe azygos venous system consists of the azygos vein on the right side and the hemiazygos and accessory hemiazygos on the left side. The azygos vein runs through the abdominal cavity along the right side of the vertebral bodies, in a cranial direction, passes through the diaphragm and reaches the mediastinum, where it forms the arch of the azygos which flows into the superior vena cava. Along its course, the azygos vein communicates with the intercostal veins on the right, the hemiazygos vein that collects blood from the left lower intercostal veins, and accessory hemiazygos vein that drains into the left upper intercostal veins. The last two, at the level of the seventh thoracic vertebra, unite and end in the azygos vein. The accessory hemiazygos vein is normally included in the length between T4 and T8. The embryological origin of the accessory hemiazygos vein is the result of an expansion in the direction of the cranial hemiazygos vein, which comes from the left upper sovracardinale vein (Dudiak et al. in Semin Roentgenol 24(1):47–55, 1989; Radiographics 11(2):233–246, 1991; Webb et al. in Am J Roentgenol 139(1):157–161, 1982).FindingsThis case report describes a rare variant of azygos vein system identified in prenatal diagnosis and confirmed by postnatal ultrasonography.ConclusionsThe observation of the patient has excluded hemodynamic alterations associated with vascular anomaly.

Azygos venous system drains the venous blood from thoracic wall. Knowledge of variations of its course and tributaries is important to cardiothoracic surgeons, radiologists and orthopedic surgeons. We observed the following variations in the azygos veins. Both azygos and hemiazygos veins were formed by union of lumbar azygos and subcostal veins of corresponding sides. The ascending lumbar vein did not drain into the azygos system. The hemiazygos vein had a larger diameter than the lower part of azygos vein and it joined azygos vein at the level of seventh thoracic vertebra. Accessory hemiazygos vein was totally absent. The azygos vein received 4th to 11th right posterior intercostal veins and also received 3rd to 6th left posterior intercostal veins. Hemiazygos vein received 7th to 11th left posterior intercostal veins.

This study aimed to validate and compare the anatomical variations of the superior intercostal veins, focusing on their origin, course, anastomoses, and destination. In addition, the results were compared with findings from other relevant studies. Fifty Korean and 16 Chinese adult cadavers were dissected for this study. The superior intercostal veins were dissected and measured. In our study of 66 specimens, the right superior intercostal vein was observed in 92.3% of cases, while the left superior intercostal vein was observed in 50%. The right superior intercostal vein was subdivided into six types based on its composition, which mainly drained the second and third right posterior intercostal veins. Similarly, the left superior intercostal vein was subdivided into eight types, primarily involving the second to fourth left posterior intercostal veins. This detailed anatomical study successfully identified and classified the various morphologic types of the superior intercostal vein and reviewed the clinical significance of this vein. The findings of this study can offer valuable anatomical evidence to physicians, aiding in their understanding and utilization of the superior intercostal vein.

We recently encountered a patient with membranous obstruction of the inferior vena cava in whom the left superior intercostal and hemiazygos veins were dilated. At chest radiography, the dilation simulated the presence of a second aortic knob and descending thoracic aorta lateral to the originals, and an aorta-in-aorta appearance was thus created.

Azygos system of veins is the main source of venous drainage from the thoracic wall. Knowledge of azygos vein anomalies could be of importance to cardiothoracic surgeons and radiologists. We report a rare variation of azygos vein as seen in an adult male cadaver aged 65years approximately. The azygos vein was formed by the union of left ascending lumbar and subcostal veins. It coursed upwards on the left side of descending thoracic aorta and crossed the left subclavian artery and the left vagus to terminate into the left brachiocephalic vein. It received left superior intercostal vein and left fifth to eleventh posterior intercostal veins. The hemiazygos and accessory hemiazygos veins were situated on the right side of the vertebral column. They received the right posterior intercostal veins and terminated into the azygos vein at the level of eighth thoracic vertebra.

During dissection of a 63-year-old female cadaver, a firm ribbon-like band was found on the left aspect of the aortic arch. Careful dissection showed that the band (6 cm long, 8 mm wide, 2 mm thick) connected the left superior intercostal vein with the accessory hemiazygos vein. Histological examination showed the fibrous structure of the band and showed the presence of a thread-like vascular lumen. The topography and venous connections of the band indicated its origin from persistence of the embryonic anastomosis between the left superior intercostal and accessory hemiazygos veins. This anastomosis derives from the rostral portion of the supracardinal vein that usually regresses on the left side but forms the terminal arch of the azygos vein on the right side. The severe atherosclerosis present in this patient at the level of the aortic arch may have enhanced the effects of arterial pressure on the adjacent venous anastomotic vessel causing reduction of blood flow and progressive fibrosis. The persistence of this venous anastomosis and its possible age-related fibrosis may have clinical relevance in central venous catheter placement.

During an educational dissection of a 72-year-old Chinese male cadaver, the hemiazygos vein (HAV) coursing the left side that drains into the persistent left superior vena cava was observed. The HAV was formed at the junction of the 9th to 11th right posterior intercostal veins, right subcostal vein, 5th to 11th left posterior intercostal veins, and left subcostal vein; it then ascended posteriorly to the thoracic aorta. After collecting the accessory hemiazygos vein, it crossed over the aorta and the pedicle of the left lung via the hemiazygos arch, then converged with a communicative branch (vein of Marshall) that emerged from the left brachiocephalic vein to form the persistent left superior vena cava and entered the pericardium at the level of the sixth thoracic vertebra. Upon opening the pericardium of our cadaver, the persistent left superior vena cava was found to drain directly into the significantly dilated coronary sinus at the level of the eighth thoracic vertebra. The azygos vein was formed by the union of the first to eighth right posterior intercostal veins and appeared to be finer and shorter than the HAV. The persistent left superior vena cava might be the result of incomplete degeneration of the left posterior cardinal vein. Knowledge of such variations could be of great value to surgeons placing peripherally inserted central catheters because incorrect placement of the azygos venous system can be detrimental to the patient. In addition, during heart surgery, awareness of such variations may prevent major complications, such as hemorrhage or damage to vascular structures, and possibly also provide new insights and perspectives to cardiovascular surgeries.

Background: This study aimed to classify Azygos vein patterns in the Eastern Indian population. Methods: During the routine dissection of MBBS in the 2018–2020 academic year, 20 formalin embalmed cadavers aged 50–70 were used to classify the azygos system. The cadaver’s age was verified by its entry into our institute’s anatomy register. The register confirmed that all cadavers used for dissection were of Indian origin. Though gender was not compared in this study, it was noted for record purposes by identifying the external genitalia and confirming it to the records. These were the exclusion criteria: 1) No major thoracic surgeries; 2) No major thoracic deformities. Azygos, hemiazygos, and accessory hemiazygos veins were also examined. Results: The Anson & McVay system was used to classify the recruited cadavers’ azygos system. The cadavers were classified into Type-1, Type-2, and Type-3. Type 2 was again subdivided into 5 subgroups and Type-3 into2 sub-groups. In one cadaver, Type-1 was observed, 17 cadavers had Type-2 azygos system, and 2 cadavers showed Type-3. Of the 17 cadavers of Type-2, 3 and 7 cadavers had Type-2A and -2B, respectively. Similarly, 4 and 1 cadavers had 2C and 2D patterns, respectively. Also, 2 cadavers showed 2E type. Of the 2 cadavers of Type-3, one was Type -3A and one Type-3B. The termination of the azygos vein vertebral level was between T2 and T4, of the hemiazygos vein was T8 to T11, and accessory hemiazygos veins were between T7 and T10. Conclusion: These variations should be well studied to avoid misinterpretation during radiological investigations and surgical interventions. KEY WORDS: Azygos vein, Hemiazygos vein, Posterior mediastinum, Radiological investigation, Variation.