2.1. Description of the “No ARSA” Method

This method is based on the demonstration of the brachiocephalic artery bifurcation to the RCA and the RSA (the “No ARSA” sign). In order to demonstrate the “No ARSA” sign, the fetus should ideally be in a supine position with a slight right-sided tilt. The three-vessel trachea view is then obtained in the axial plane, as described by Yagel et al. [17] (Figure 1A). It includes the ductus arteriosus branching from the pulmonary trunk, a transverse section of the aortic arch, located to the right of the ductus arteriosus, and finally, cross sections of the superior vena cava and trachea, located to the right of the aorta. From the 3VT (three-vessel trachea) plane, the BCA is visualized arising from the aortic arch (Figure 1B) by slightly rotating the transducer towards the sagittal plane.

“No ARSA” plane acquisition: The brachiocephalic artery arises from the aortic arch and crosses anterior to the trachea and towards the right side of the fetus. The angle of insonation to acquire the corresponding plane to demonstrate (A) three-vessel trachea (3VT) view (B) brachiocephalic artery origin (C) brachiocephalic artery bifurcation, the “No ARSA” sign. ARSA, aberrant right subclavian artery; D, Ductus arteriosus; A, Aortic arch; B, Brachiocephalic artery.

By further rotation of the transducer towards the sagittal plane, the brachiocephalic artery’s long axis is exposed with its bifurcation to the right carotid artery and the right subclavian artery (Figure 1C and Figure 2 and Video S1). Once the BCA bifurcation (the “No ARSA” sign) is demonstrated, ARSA is ruled out.

The “No ARSA” sign. The brachiocephalic artery (I) arises from the aortic arch and bifurcates into the RCA (right carotid artery), which courses as a continuum of the brachiocephalic artery cranially and the RSA (right subclavian artery) coursing posterolateral (a) at 14.3 weeks and (b) at 21.2 weeks.

If the bifurcation is not visible, the single vessel is then followed up to the neck to confirm that it is the right carotid artery and to ensure the bifurcation was not overlooked (Video S2). Once the bifurcation of the first vessel of the aortic arch is ascertained to be absent, an ARSA is suspected. In order to validate this method, all fetuses were also scanned using the conventional method described by Chaoui et al. [1] (Figure 3).

Negative "No ARSA" sign: The RCA emerging as a single vessel from the aortic arch with no visible bifurcation. Simultaneously, an ARSA is visualized coursing behind the trachea towards the right arm (a) at 14.2 weeks and (b) at 32.5 weeks. RCA, Right carotid artery; ARSA, Aberrant right subclavian artery. A, Aortic arch.

Examinations were performed transabdominally or transvaginally, depending on gestational age, using a Voluson E10 ultrasound machine (GE Healthcare, Milwaukee, WI, USA) with either an abdominal RM6C 2–6 MHz convex probe or a vaginal RIC 6–12 MHz probe, as appropriate. Generally, a transvaginal approach was used at 12–15.6 weeks of gestation and a transabdominal approach from 16 weeks and over.

Maternal demographic information, medical history, fetal anomaly scan results, prenatal genetic evaluation and postnatal outcomes were collected. A comparison of maternal and fetal parameters was performed between the “No ARSA” and ARSA groups.

The study was approved by the Institutional Review Board (5345-18-SMC).