Sonographic imaging of the fetal azygous vein. Normal and pathologic appearance.

Sonologists should be familiar with the frequency of resolution and the ultrasonic appearance of the normal fetal azygous vein. In this study, 66 consecutive uncomplicated pregnancies were scanned to determine the frequency of imaging the fetal thoracic azygous vein. Between 21.7 and 30 gestational weeks, the azygous vein could be imaged in 50% of the cases and measured 1-2 mm in caliber. In the last 10 weeks of pregnancy, the azygous vein could be imaged in 98% of the cases and measured 2-4 mm. A case of fetal azygous continuation of the inferior vena cava is shown where the vein was abnormally dilated to a caliber of 8 mm.