LAUSR

Prenatal dilatation of the azygos vein is a marker for disruption of the embryologic formation of the cardiovascular system. We present a case of a dilated azygos vein due to obstruction of the inferior vena cava (IVC) by an enlarging fetal urinoma. A right-sided posterior cystic mass was detected at 22 weeks’ gestation on a routine scan (Figure 1A). By 26 weeks, the expanding urinoma (Figure 1B) and resultant compression of the IVC by the left lateral displacement of the liver due to the enlarging retroperitoneal mass impaired drainage from the lower body. Dilatation of the azygos vein (behind the heart in the 4-chamber view) was shown at 30 weeks (Figure 1C) with the Azygos arch emptying into the superior vena cava (SVC; Figure 1D). The fetus was delivered spontaneously at 34 weeks, and laparoscopic nephrectomy was performed. 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. Although not the primary venous system in