Venous valves of the azygos arch: A cadaveric study

Purpose

The existence of valves in the azygos vein are not discussed in depth in the current body of literature. Although the clinical relevance of the valves in these veins are not well understood, these valves may have implications in diagnostic imaging where their appearance on imaging studies can impact interpretation. This study aims to use cadaveric dissections to determine the anatomic prevalence and morphology of valves in the arch of the azygos vein in comparison to current data reported from clinical imaging studies and anatomy textbooks.

Methods

Approval of this research study on human cadaveric specimen was sought from the St. George's University Institutional Review Board (IRB) and was deemed exempt from full review (IRB – 16015). This research project involved 47 azygos veins dissected from human cadaveric donor specimen. Azygos veins were harvested from the level of the diaphragm to the inflow into the superior vena cava for gross inspection of valve presence and morphology. The data collected was recorded and sorted by sex, valve presence, number and morphology and valve location. Chi square analysis was performed to assess possible relationships in valve findings based on sex. A brief search of the literature using the keywords “azygos vein” and “valves” was conducted to see the current understanding of azygos valve prevalence.

Results

Of the donor specimen, 53.2% (25 of 47) were male and 46.8% (22 of 47) were female. Of the 47 cadavers that were dissected, 89.3% (42 of 47) were found to have valves in the azygos vein, while 10.6% (5 of 47) were found to have none. The azygos vein contained mostly one valve along its length, mainly located in the arch. The valves were unicuspid (8.5%; 4 of 47), bicuspid (70.2%; 33 of 47) or tricuspid (10.64%; 5 of 47). Dividing the arch of the azygos into quartiles, valves were found most commonly in the third quartile of the distance from the opening of the right superior intercostal vein into the azygos vein to the superior vena cava. Four cadavers had multiple valves, each with varying valve morphology. The length of the cusp of the bicuspid valve ranged from 10 mm to 12 mm.

Conclusion

This study shows that the azygos vein contains valves, predominantly within the arch at a prevalence of 89.3%. The presence and variability in morphology of valves in the azygos vein and its potential implications for contrast appearance on imaging studies is clinically important. Radiologists should have a working knowledge of the different appearances of azygos arch valves to minimize the risks of confusing normal variations with thoracic pathology. Though not commonly described in anatomy texts, the findings of this research not only add more detail to the historical cadaveric study information on azygos vein valves, but also shows that the prevalence of azygos arch valves surpasses the numbers reported in clinical studies. As such, it provides support for the inclusion of azygos arch valves in anatomical textbooks and in the teaching of image interpretation.