The interrupted inferior vena cava (IVC) with azygos continuation to the superior vena cava (SVC) arises from a failure to form the right subcardinal–hepatic anastomosis, resulting in absence of the hepatic segment of the IVC. This anomaly characterizes left atrial isomerism (Polysplenia) which is commonly associated with atrioventricular septal defect and complete heart block. The sonographic landmark is a dilated azygos vein alongside the aorta on the abdominal circumference plane and four-chamber view plane (Yagel S., et al., 2010).
Interrupted IVC with azygos continuation to the SVC has also been reported as an isolated entity, in which cases it is usually clinically silent. Our featured case shows an isolated interrupted IVS with azygos continuation to the SVC.
Interestingly, the ratio of the diameters of Azygos/Descending Aorta at the height of the four-chamber view is constant during pregnancy and it may be used as a useful maker for prenatal screening and diagnosing of interrupted inferior vena cava. The median of AZ/DAO ratio in normal group and IIVC group were 0.38 (ranged from 0.24–0.62) and 0.70 (ranged from 0.64–0.78), respectively (Xie H. and Wu, L., 2014).
- Yagel, S., Kivilevitch, Z., Cohen, S. M., Valsky, D. V., Messing, B., Shen, O. and Achiron, R. (2010), The fetal venous system, Part II: ultrasound evaluation of the fetus with congenital venous system malformation or developing circulatory compromise. Ultrasound Obstet Gynecol, 36: 93–111. doi:10.1002/uog.7622
- Xie, H. and Wu, L. (2014), OC02.04: Azygos vein/descending aorta ratio in normal fetuses and fetuses with interrupted inferior vena cava. Ultrasound Obstet Gynecol, 44: 4. doi:10.1002/uog.13472