Variations in Azygos Venous System in The Eastern Indian Population: A Cadaveric Study

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.