Resumen de Analysis of multiple variations in azygos venous system anatomy with its classification: A cadaveric study

Apurba Patra, Rajan K. Singla, Harsimarjit Kaur, Vishal Malhotra

• The azygos venous system varies greatly in mode of its origin, course, number of vertical channels, number of horizontal anastomoses and nature of termination. Anatomical knowledge of such variations is of immense importance in radiological investigations and surgical intervention of posterior mediastinum pathologies. The present study was undertaken on 30 adult embalmed cadavers aging between 40–65 years, to determine the anatomical variations of the azygos system and to classify accordingly. The vertebral level and diameter of the azygos, hemiazygos, accessory hemiazygos veins at their origin and terminations were also observed. The azygos system was classified into 3 types as per the Anson & McVay system: primitive (type I), transient (type II) and unicolumnar (type III). Type II was further subdivided into 5 subgroups (A to E) according to the number of retroaortic communications. Type I was observed in 1 case (3.33%), type II in 27 (90%) and type III in remaining 2 cases (6.67%). The vertebral level of termination of the azygos, hemiazygos, accessory hemiazygos veins were between T2 and T3, T6 and T10, T6 and T9 respectively. Variations in the formation of azygos system is not an uncommon phenomenon and these variations may easily mislead the radiologists while performing CT/MRI of posterior mediastinum or cardiothoracic surgeons while performing vascular surgeries in this region.