Agenesis of the ductus venosus: three-dimensional power Doppler reconstruction

Abstract

The ductus venosus (DV) is an important fetal vascular structure that connects the umbilical venous system to the inferior vena cava (IVC) near its insertion point into the right atrium1. It allows 20–30% of the umbilical blood to bypass the liver in utero and reach the heart rapidly, thus increasing the flow of well-oxygenated blood to the cephalic and coronary circulation. The DV therefore plays a key role in increasing the shunt of oxygenated blood to the heart and decreasing placental return during hypoxemia and hypovolemia1,2. For several years, improvements in ultrasound techniques, such as two-dimensional (2D) and threedimensional (3D) ultrasound reconstruction, have made it possible to identify numerous malformations that were previously undetectable antenatally, including agenesis of the DV3, which is associated with various morphological and cytogenetic abnormalities. Examination of the DV has been used in referral centers to refine diagnoses involving cardiac, extracardiac and chromosomal anomalies2 as well as in first-trimester screening for Down syndrome in the high-risk population4. The DV pulsatility index for veins can be used as a continuous variable, in combination with nuchal translucency (NT) measurement, to increase specificity in the identification of congenital heart defects5. We report here the case of a 31-year-old primigravida, referred at 35 weeks of gestation to our prenatal center after the abnormal finding at third-trimester ultrasound of a highly dilated IVC (4.1 mm) and umbilical vein. Firstand second-trimester findings had been unremarkable. Combined marker screening in the first trimester indicated a 1/554 risk for Down syndrome, with NT on the 60th percentile. The only morphological abnormalities found during the third-trimester examination were the dilated IVC and umbilical vein. Suspecting agenesis of the DV, we performed a color Doppler ultrasound examination. Looking for an abnormal course or flow in the umbilical vein, we found that it was connected directly to the IVC and the flow velocity was high. To clarify the situation, 3D volume datasets were acquired with transverse and sagittal sweeps over the abdominal region. The umbilical vein and IVC were reconstructed using the glass-body rendering (angiographic) mode to optimize examination of these vessels. To highlight their abnormal connection, we then used the Magicut postprocessing application (Figure 1). This 3D power Doppler reconstruction demonstrated the anomalous course of the dilated umbilical vein, which was connected directly to the dilated subdiaphragmatic IVC and bypassed the liver. Fetal echocardiography showed substantial disproportion in the diameters of the IVC and superior vena cava at the points of insertion into the heart: 4.1 mm vs 1.2 mm. No features of cardiac decompensation or morphological abnormality were seen. The patient was offered amniocentesis for karyotype determination because agenesis of the DV is associated with a high rate (17%) of chromosomal abnormalities2; the karyotype was normal. The remainder of the pregnancy and delivery were uneventful, and the child appeared healthy. Little is known about the consequences and clinical implications of agenesis of the DV6. This anomaly affects approximately 6/1000 fetuses in a high-risk population. The few reports in the literature of an absent DV are associated with three different abnormal patterns: the umbilical vein may bypass the liver and then connect to the subdiaphragmatic IVC or to the iliac or renal veins, it may connect directly to the right or left atrium, or it may connect directly to the portal vein without giving rise to the DV2,7. DV agenesis is associated with congenital morphological abnormalities in approximately 65% of cases and with cytogenetic abnormalities in 17%2,8. The cardiac anomalies associated with DV agenesis, which occur in 48% of cases, include atrial and ventricular septal defects, tricuspid atresia, double outlet right ventricle, pulmonary atresia and transposition of the great arteries7,9. Other common associated anomalies involve the gastrointestinal system (duodenal atresia and tracheoesophageal fistula), the genitourinary system (bilateral hydronephrosis and ectopic kidney) and the musculoskeletal system