A novel systematic approach to the evaluation of the fetal venous system

Azygos Vein Z Scores in Healthy Fetuses and Fetuses With Venous Malformations Related to the Azygos Vein

“…In our opinion, there are 2 advantages to measuring the azygos vein on the 4‐chamber view rather than on the 3‐vessel view: first and most important, the former plane is included in the cardiac screening views of the second‐trimester anomaly scan 12 ; in addition, in our experience, the azygos vein is easier to identify and, hence, measure on the 4‐chamber view than on the 3‐vessel view. The azygos vein appears to be approximately 3 times smaller in diameter than the aorta on the 4‐chamber view 2 . The azygos vein‐to‐descending aorta ratio was constant at 0.4 throughout pregnancy in a previous study 4 .…”

“…It usually starts from the right ascending lumbar vein at or below the level of the renal veins, lies close to the right posterior aspect of the descending aorta, and courses upward through the diaphragm, receiving in its course the 4th to 11th right posterior intercostal veins as well as the hemi‐azygos vein. At the level of the 4th thoracic vertebra the azygos vein arches forward and drains into the superior vena cava 1 , 2 . Sonographic assessment of the azygos vein is consistently achieved in the second and third trimesters and, sometimes, in the first trimester of pregnancy 3 , 4 …”

Prenatal Diagnosis of a Urinoma and Dilated Azygous Vein

“…Yagel et al described the embryologic development of the fetal venous system from the 4 pairs of primitive embryonic vessels. The azygos vein derives from the cardinal vein and is a collateral venous pathway draining the lower body of the fetus and connecting the (IVC) to the SVC . It lies adjacent to the right side of the vertebral body and normally is only a few millimeters in diameter.…”

“…It lies adjacent to the right side of the vertebral body and normally is only a few millimeters in diameter. Although not the primary venous system in the fetus, it retains its ability to dilate and serve as a shunt when major pathways of venous return either fail to develop or become obstructed …”

“…The most common prenatal condition associated with dilatation of the azygos vein is failure of the hepatic segment of the IVC to form. This condition occurs frequently in left atrial isomerism as a part of heterotaxy syndrome when the right subcardinal vein fails to anastomose with the hepatic sinusoids to form the hepatic segment of the IVC …”