A semi‐quantitative approach to variation of the azygos vein course

Abstract

The azygos vein (AV) is typically described (illustrated) as ascending vertically on the right of thoracic vertebrae. Most thoracic vein studies have focused on tributary patterns, but some have noted more leftward AV courses. This study statistically documents variation in AV course independent of tributary patterns. A more statistical approach to the probable position of AV at different vertical levels may aid clinicians in locating and assessing it in clinical contexts. The AV course was exposed in 84 cadavers by removing overlying viscera between the aortic hiatus and tracheal bifurcation. Subjectively, non-pathological specimens were digitally photographed in anterior view. For each photo, a scaled grid was used to mark the horizontal position of the AV center at each of five vertical levels. The summated numerical distributions showed the following: ∼5% of the AVs ascended on the right side (classical) position, ∼30% did not cross the midline, ∼70% included part or all of their course left of the midline, and ∼14% reached the extreme left side. Based on this data, the modal AV course (1) begins at, or to the right of, the midline, (2) deviates leftward, (3) crosses the midline below mid-level, (4) reaches a leftward maximum at about 3/5 of its course, (5) then deviates rightward (often only reaching the midline at the uppermost level). In several noticeable cases, the leftward maximum was associated with large connections to left-side veins, suggesting a possible tension mechanism exerting traction on the AV over time.

Misplacement of Tunneled Hemodialysis Catheter into Azygos Vein: Left or Right Jugular Insertion Has Similar Susceptibility

“…According to Kutoglu et al [33], apart from right-sided AV-SVC connection, AV might also drain into SVC from the posterior-and left-posterior directions. These 3 patterns of AV-SVC anastomoses are verified in Bales' article regarding AV course variations [40].…”

The impact of aging on the course of the azygos vein

“…Kagami and Sakai suggested that the left shift of AV is caused by the aging process [13]. In addition, Bales reported that the point of maximum inflection (extreme left point) of the AV course coincides with large left-toright crossover connections, and argued that these crossover veins may exert a leftward traction on AV over time, presumably resulting in a gradual shift [14]. We believe that the left shift of AV may be caused in part by the aging process.…”

“…Regarding the reason for the AV left shift, Bales reported that crossover veins may exert a leftward traction on AV over time, resulting in a gradual focal shift [14]. We hypothesized that aged cadavers had a tendency of having crossover veins at the extreme left shifting point of AV, which may cause a left shift of the entire AV by its traction.…”

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 ]. Also, Nathan suggested that the existence of asymmetric osteophytes on the thoracic vertebrae could explain the deviation of the AV due to mechanical pressure to the left [ 7 ].…”