148: The Three Vessel View: Identifying normal and abnormal distances between the pulmonary artery and aorta

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Vascular rings though rare, can be missed despite the addition of 3 vessel view on complete obstetric scans. Prior studies have noted an increased distance between the aorta and pulmonary artery in cases of vascular ring, but this has not been quantified. The primary goal of the study is to compare the distance between the pulmonary artery and aorta in vascular ring cases to non-anomalous fetuses. The study was also designed to create a nomogram for the intervessel distance in non-anomalous fetuses between 18 to 26 weeks of gestation. This is a retrospective study of ultrasound images obtained from non-anomalous fetuses and fetuses affected by vascular rings. Subjects included were patients over 18 years old undergoing anatomy screening between 18 and 26 weeks of gestation. Patients were included if the 3 vessel view was of adequate quality with ability to measure the distance between the pulmonary artery and aorta, and no fetal anomalies were present. A total of 135 non-anomalous fetuses, 15 per gestational week, were chosen as the sample size. Of the vascular ring cases the mean gestational age at diagnosis was 22 weeks ± 1.37 weeks with a mean intervessel distance of 3.42mm ± 0.47. Of the non-anomalous fetuses the mean gestational age was 22 weeks ± 2.6 weeks with a mean intervessel distance of 1.58mm ± 0.25. A Welch’s T test was performed to compare the 2 groups, t=8.81 with a p=.001. This shows that there is a significantly larger intervessel distance in cases of vascular rings. Gestational age and chest circumference were found to significantly predict the intervessel distance in non-anomalous fetuses, F(1,134)= 67.7, P< .0005 and F(1,134)= 62.9, P< .0005. The regression equation for gestational age is intervessel distance(mm) = .057(Gestational age)+.302. For chest circumference(mm) the intervessel distance(mm) = .006 (Chest circumference)+.709. This study can provide an additional diagnostic tool to detect vascular rings in the 3 vessel view which will be increasingly important as this view is now included in complete obstetric scans per the AIUM guidelines.View Large Image Figure ViewerDownload Hi-res image Download (PPT)