Anomalous azygos veins - its embryological basis and clinical significance

Abstract

INTRODUCTIONThe Greek root zyg refers to a pair. 'A-' means not. Thus, azygos means unpaired. The azygos vein is unpaired in that there is only one in the body, mostly on the right side. While there is the hemiazygos vein and its accessory on the left side of the body, they are considered tributaries of the azygos vein rather than its left-side equivalent.1 The azygos system includes those veins which are straight in course, paravertebral in position, and not accompanied with the corresponding arteries.These veins are provided with valves, and drain most of the blood from the back and from the thoracic and abdominal walls. The azygos system communicates with the vena caval system in front, and with the vertebral venous plexus behind. The terminal veins of this system are the azygos, hemi-azygos and accessory azygos veins. The azygos vein is inconstant in the mode of origin. 2Although there are complete valves in some tributaries of azygos veins, there are usually incomplete valves varying between one and four in the azygos arch. Thus, the azygos vein functions as a collateral for the superior and ABSTRACT Background: The anatomical knowledge of the variability of the azygos venous system is important for the surgical interventions of the posterior mediastinum and also during radiological investigations/diagnosis especially CT and MRI. The variant azygos venous system might be confused with thoracic aorta aneurysms, lymphadenopathy and tumours of posterior mediastinum. Methods: The present study was undertaken on 10 embalmed adult human cadavers irrespective of sex, used for undergraduate dissection from the Department of Anatomy, Mandya Institute of Medical Sciences, Mandya. In this present study, formation, course and termination pattern of azygos system of veins was observed in 10 dissected human cadavers. Out of which 2 cadavers showed different types of variations. Results: In the present 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. Conclusions: Accurate knowledge about these kinds of variations is very important to identify, especially in the computed tomography and magnetic resonance imaging of mediastinum. The abnormal azygos venous system may easily be confused with aneurysm, lymphadenopathy and other abnormalities like tumor. It is important to keep these kinds of variations in mind while performing the mediastinal operations or surgery of large vessels.

A Left-sided Azygos Vein in a Cadaver: Anatomical and Surgical Considerations

“…Possible explanations for the anomalous course of the AV have to be given, beyond the rare occasion of independent left AV (persistence of the early embryonic form) [ 11 ]. Bales attributed the displacement of the AV to crossover veins, which gradually over time transpose the vessel from its regular course [ 12 ].…”

A Cadaveric Study of Azygos Venous System

“…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].…”

Anatomical Variation of the Azygos System of Veins - Case Report

“…The system is found parallel to the vertebral column and is not followed by correspondent arteries. 3 The AV and the HV are generally formed by the union of posterior branches of the inferior cava and/or renal veins with the ascending lumbar veins. The AV goes up at the right side of the vertebral column, finishing in the superior vena cava.…”

“…2 The ASV has been extensively studied, and anatomical variations on its constituents are not so rare. 2,3 These variations differ from each other according to their origin, caliber, course, and termination. 4,5 This fact can explain why there are so many attempts to classify the ASV, 4,6-8 but there still is no consensus about these classifications.…”