Dilation of the azygos vein is a sign of increased right atrial pressure and is usually seen when there is also an increase in the width of the vascular pedicle.
The diameter of the azygos vein varies according to the positioning.
In the standing position a diameter > 7 mm is most likely abnormal and a diameter > 10 mm is definitely abnormal.
In a supine patient > 15 mm is abnormal. 
An increase of 3 mm in comparison to previous films is suggestive of fluid overload. 
The difference of the azygos diameter on an inspiration film compared to an expiration film is only 1mm. 
This means that the diameter of the azygos is a valuable tool whether or not there is good inspiration. #Clinical #Radiology #CXR #CHF #Azygous #Vein #AzygousVein #Dilatation #RadiologyAssistant