A unique variation of azygos system of veins

Abstract

Knowledge of variations of azygos and hemiazygos veins is of importance to cardiothoracic surgeons and radiologists during various surgical, radiological, and echography techniques. We report some unique variations of azygos system of veins observed during dissection classes for undergraduate medical students. The azygos vein was formed as usual by the union of right subcostal and ascending lumbar veins. The vein ascended upward and to the left to reach the midline at the level of the 9th thoracic vertebra. After ascending till 5th thoracic vertebra, it gradually inclined to the right of midline and terminated by opening into the superior vena cava at the level of the 3rd thoracic vertebra. There was no major variation in the tributaries of the azygos vein on the right side, except that the right superior intercostal vein crossed behind the azygos vein from right to left and opened into the left side of the azygos vein. Further, two anastomotic veins connected the 10th, 11th and 12th posterior intercostal veins with each other to form two anastomotic circles on the right side of 10th to 12th thoracic vertebrae. The hemiazygos vein bifurcated on the left side of the 10th thoracic vertebra and the two ends opened into the azygos vein at the level of 9th and 10th thoracic vertebrae forming a venous circle in front of the 10th thoracic vertebra. The course of accessory hemiazygos vein was noteworthy. Instead of its classic descending course, the vein ascended upward from the left side of the 8th thoracic vertebra till the 6th thoracic vertebra before opening into the azygos vein.

An Unusual Benign Cause of an Alarming Finding on Chest-X ray: A Case Report of Widened Mediastinum due to Rare Congenital Abnormality (Azygos Vein Continuation of Inferior Vena Cava)

“…Veins that drain into the Azygos are the right superior intercostal vein, 5 th –11 th right posterior intercostal veins, hemiazygos vein, accessory hemiazygos vein, pericardial, bronchial, and esophageal veins. The Azygos provides collateral venous circulation between the SVC and the IVC with two ways shunt since it has few to no valves [6]. As such, the Azygos vein has a significant clinical role in cases of increased venous pressure.…”

A Cadaveric Study of Azygos Venous System

“…The accessory hemi-azygos vein is absent and the hemi-azygos vein is present draining into the azygos vein. In 2 male cadavers there were 3 transverse channels connecting the accessory hemiazygos and hemiazygos with the azygos vein [11]. Badagabettu S N, literature survey also revealed a case where the hemiazygos vein was absent with the presence of right and left azygos veins [12].…”

Split Azygos Vein: A Case Report

“…Studies by Seib (1934) Nayak and Soumya [10] have described a reversed azygos system with the azygos shifted to the left side and draining into the brachiocephalic vein and the accessory and hemiazygos system shifted to the right side of the body. Badagabettu et al [11] have reported a hemiazygos vein with multiple linkages to the azygos vein across the midline. Neither of the cases reported by these authors or others was similar to our case, where two more or less vertical venous chains converged into a single vein inferiorly to drain into the IVC and, just prior to this, formed a circular venous plexus.…”