A Study of Anatomical Variations in Azygos System of Veins

INTRODUCTION : Variations are commonly seen in the azygos system of veins because of its complex embryological development. AIM : The aim is to study the variations of the azygos system of veins under the following parameters, Mode of formation of the azygos vein, Course of the azygos vein in relation to the midline of vertebral Column, Level of arching of the azygos vein and Level of termination of azygos vein into the superior venacava, Level of termination of the hemiazygos vein, the accessory, hemiazygos vein Diameter of the azygos vein, the hemiazygos veins at the level of termination Type, pattern of the azygos system of veins. MATERIALS AND METHODS : The Azygos venous system was studied and analyzed for the parameters taken, by dissection method and also by analyzing radiographic images. This study was done in Anatomy Department of Stanley Medical College on 30 conserved human cadavers between the years 2013 and 2015. Radiographic images 20 in number were obtained from Radiology Department, Stanley Medical College and analyzed. The results are charted out, statistically analyzed and correlated with the findings of already existing studies. OBSERVATION : Azygos vein is present in all the specimens (100%). Hemiazygos vein is absent in 14%. Accessory hemiazygos vein is absent in 28%. Out of 30 cadaveric specimens studied, in 90% the azygos vein is formed by a single root that is the lateral root. Azygos vein is present to the right of midline of the vertebral column in 62 %. The level of termination of the azygos vein is at fourth vertebral level in 64 %. Azygos lobe is noted in the right lung in one radiologic specimen. The level of termination of the hemiazygos vein is at the eighth and ninth thoracic vertebral level in 39.5 % each. The mean diameter of the azygos vein and hemiazygos vein just at their termination are 6.9 +/-2.1mm and 5.05+/-1.3 mm respectively. Among the 50 specimens analyzed 86.7% belongs to type II, 6.7% to type III and 3.3% to type I. Type I Group 1 is present in 3.3%, Type II Group 2 in 23.3%, Group 3 in 3.3%, Group 4 in 13.3%, Group 5 in 10%, Group 6B in 6.7% , Group 7 in 20% , Group 9 in 6.7% , Group 10 in 3.3 % , and Type III Group 11 in 6.7%. 3.3% is classified as atypical. There are no associated anomalies of the superior and the inferior vena cava. CONCLUSION : It is very important to identify the anomalies of the azygos venous system in the computed tomography and magnetic resonance imaging of mediastinum. It is important to have knowledge of these kinds of variations while performing the mediastinal operations or surgery of large vessels