A CADAVERIC STUDY OF AZYGOS VENOUS SYSTEM

Address for Correspondence: Dr. M Shilpa, Postgraduate, Department of Anatomy, Mysore Medical College & Research Institute, Mysore. Karnataka, India. Mobile No: 7411543525 E-Mail: shilpa_ramling@yahoo.co.in Background: The azygos venous system consists of the azygos vein on the right side and the hemiazygos and accessory hemiazygos on the left side. The latter two are said to be the tributaries rather than the equivalent of the azygos vein. This unpaired venous system is said to be full of anatomical variations and hence of much clinical significance. Aim: To study and report the prevalence of any anatomical variation of azygos venous system. Materials and Methods: The present study was carried out in the Department of Anatomy, MMC & RI, Mysore, over a period of 2 years. A total of 20 cadavers irrespective of age and sex were dissected for study purpose. The entire course of the azygos venous system in these 20 cadavers was carefully dissected and documented. Observations: In present study among 20 cadavers, 2 adult male cadavers showed variation during dissection of posterior thoracic wall, we found that in one cadaver azygos vein running on left side of vertebral column, hemiazygos and accessory hemiazygos veins were absent. In another cadaver we found that arch of azygos on left side with osteophytic changes of vertebral column. Conclusion: Venous abnormalities often complicate mediastinal surgery with intra operative hemorrhage. Prior knowledge of possible anatomical variations may help the surgeons to reduce the risk of such events. Also presence of such variations may lead to misinterpretation of thoracic CT and MRI findings of the posterior mediastinum.

A total of 20 cadavers irrespective of age and sex were obtained from the Department of Anatomy, MMC & RI, Mysore, over a period of 2 years.The entire azygos venous system (azygos vein, hemiazygos vein, accessory hemiazygos vein) was carefully dissected from its formation, course, tributaries and termination.
Following observations were made.

MATERIALS AND METHODS
In the present study, the origin, course and termination of azygos venous system was noted.
One (1) adult male cadaver showed variation in course of azygos vein, absent hemiazygos and accessory hemiazygos vein.
One (1) cadaver showed variation in arch of azygos vein.In Uma shivanal study, normal azygos venous system was found in 8 specimens accounting for 80%.Variations were found in 2 specimens (20%); one specimen presented with connection between accessory hemiazygos vein and hemiazygos vein, 3 transverse channels across vertebral column and the other specimen showed absence of accessory hemiazygos vein and shifting of azygos vein towards midline [14].This unpaired venous system is said to be full of anatomical variations and hence of much clinical significance.Venous abnormalities often complicate mediastinal surgery with intra operative hemorrhage.Prior knowledge of possible anatomical variations may help the surgeons to reduce the risk of such events.Some variations of the azygos venous system can easily be confused with pathological conditions such as aneurysms, tumors and enlarged lymph nodes.Also presence of such variations may lead to misinterpretation of thoracic CT and MRI findings of the posterior medistinium tumors.

INTRODUCTION
International Journal of Anatomy and Research, Int J Anat Res 2017, Vol 5(3.2):4299-03.ISSN 2321-4287 DOI: https://dx.doi.org/10.16965/ijar.2017.317 in front, and with vertebral venous plexuses behind [1].The terminal veins of this system are the azygos, hemiazygos and accessory azygos veins.The azygos vein is inconstant in origin.On developmental backgrounds, it may arise as lumbar azygos vein.If it does not arise as lumbar azygos, then trunk is formed by the union of the right sub costal and right ascending lumbar Azygos venous system includes those veins which are straight in course, paravertebral in position, and not accompanied with corresponding arteries [1].These are provided with valves; drain most of the blood from back and from the thoracic and abdominal walls.The azygos system communicates with the vena caval system veins [1].In the thorax, the azygos vein passes upwards in front of the lower eight vertebra in the posterior medistinum, opposite the fourth thoracic vertebra, it arches forwards above the root of the right lung and pierces the fibrous pericardium.The arch of azygos vein is a content of middle medistinum.Sometimes there may be variation in termination the arch of azygos splits the apex of right lung and lodges in a fissure where it is suspended by a mesentery [2].Medial part of the split apex is known as the lobe for azygos vein of right lung.The hemiazygos vein begins by the union of the left ascending lumbar and left sub costal veins, and communicates below with the left renal vein.The accessory azygos vein begins as a continuation of the left fourth posterior intercostals vein, and receives the blood from the left fifth, sixth, seventh intercostals veins as it descends .Finally it terminates in the azygos vein opposite T7 vertebra [2].The azygos vein is a collateral venous pathway, becoming a vital shunt if major pathways of venous return are obstructed [3].

Fig. 1 :
Fig. 1: the azygos vein is formed by right and left ascending lumbar vein, its course is on the left side of vertebral column, right and left posterior intercostal veins directly draining into azygos vein, absence of hemiazygos and accessory hemiazygos veins.

Fig. 2 :
Fig.2: The azygos vein is on the left side and arch of azygos is also on left side arching on left lung but it deviates to right side.The vertebral column shows osteophytic lesions which may be one of the reasons for variation in course of azygos vein.