Introduction
Both the double aortic arch (DAA) and the right aortic arch with the mirror-image branches (RAA-MB) are considered as abnormal development of the aortic arch. However, their prognoses are quite different. Therefore, it is necessary to make a differential diagnosis of the DAA and the RAA-MB in the fetus, which is helpful for the prenatal prognosis consultation. Previous studies suggested that the three-vessel-trachea view and their adjacent view could be used to distinguish them.1 However, if there is hypoplasia or atresia in the posterior part of the left aortic arch, its manifestations are very similar to those of the RAA-MB, making it very difficult to distinguish both. The 3D STIC technique increased the sensitivity of fetal echocardiography for detecting arch anomalies.2 The DAA forms an ”O” vascular ring, 1, 3 while the RAA-MB itself does not.4 The main difference between the two is to observe whether the first branch of the ascending aorta is connected with the descending aorta. However, the right aortic arch is usually higher than the left one, which cannot be displayed completely in one view. Moreover, in the same view, the angle between the right aorta and the first vessel branch can be shown. Therefore, we hypothesized that there might be a difference among the angle between the two arches of the DAA and that between RAA and the first branch of the right arch. To our best knowledge, this is the first study to elucidate on that difference. Based on two-dimensional color echocardiography, the angles between the two aortic arches and the RAA and its first branch were measured to distinguish them in this study.