Azygos Arch Valves: Prevalence and Appearance at Contrast-enhanced CT

PURPOSE: To evaluate the prevalence and appearance of azygos arch valves at intravenous contrast material-enhanced computed tomography (CT). MATERIALS AND METHODS: Findings of 309 intravenous contrast-enhanced spiral CT examinations of the chest were retrospectively reviewed. The presence of contrast material reflux into the azygos arch and of a focal bulge in the azygos arch was recorded. An azygos valve was considered present if contrast material with a curvilinear posterior contour was seen in the azygos arch. The χ² test was used to compare the frequency of contrast material reflux into the azygos vein for high and low rates of contrast material injection and for right and left arm injection. RESULTS: Reflux of contrast material into the azygos arch occurred at 154 (49.8%) of 309 examinations, and valves were seen on images of 105 (68.2%) examinations. A focal bulge was seen in the azygos arch on images of 86 (81.9%) of 105 examinations with an azygos valve. Contrast material refluxed more frequently into the azygos vein in examinations with high rates of injection (83 of 128 examinations, 64.8%) than in those with low rates of injection (71 of 181, 39.2%, P <.001). Among the patients with high rates of injection, contrast material refluxed more frequently into the azygos vein with the right arm injection than with left arm injection (53 of 70, 76% vs 30 of 58, 52%, P < .01). Refluxed contrast material appeared as discrete collections within cusps of the azygos valves on images of 69 (44.8%) of 154 examinations. CONCLUSION: Valves in the azygos arch are common and more frequently seen at CT when high injection rates and right arm injections are used.