Coronal view as a complementary ultrasound approach for prenatal diagnosis of aberrant right subclavian artery

Abstract

Aberrant right subclavian artery (ARSA) is associated with chromosomal abnormalities, mainly Down syndrome, and congenital heart disease1-5. ARSA is caused by abnormal regression of the primitive right aortic arch between the right subclavian artery and the right common carotid artery. As a result, the aortic arch branches into four arteries instead of three, and the ARSA originates distal to the left subclavian artery at the level of the aortic isthmus. ARSA follows an oblique course behind the trachea and esophagus to reach the right arm. In 2005, Chaoui et al.2 described the methodology for assessment of fetal ARSA in the transverse three vessels and trachea view, in which the anomalous origin of ARSA, close to the ductus arteriosus, and its retrotracheal course can be visualized (Figures 1a and c). This group subsequently showed how to visualize fetal ARSA in a longitudinal view6, in which the artery arises as a fourth and distal vessel from the aortic arch; however, in this view the retrotracheal course is not identifiable. As Quarello and Carvalho7 remarked, although several anatomical variations can manifest as an aortic arch with four vessels in the longitudinal view, in cases in which ARSA originates anteriorly from the aortic arch, visualization of four supra-aortic vessels is not possible. (a,b) Color Doppler ultrasound images of fetal aberrant right subclavian artery (ARSA) at 20 weeks' gestation. (a) Transverse view showing ARSA in the three vessels and trachea plane with its origin at the level of the aortic isthmus and with a retrotracheal course (arrows). (b) Coronal view showing ARSA arising from the aorta with an oblique course towards the right shoulder. (c) Schematic representation of the transverse (A) and coronal (B) planes in a fetus at the level of the ARSA. Ao, aorta; DA, ductus arteriosus; DAo, descending aorta; P, pulmonary artery; S, spine; T, trachea. We illustrate how this vessel can be visualized in the coronal plane. In order to assess ARSA, we obtain a coronal view of the fetal thorax, posterior to the trachea and anterior to the spine, until we are able to see the thoracic descending aorta. Highly sensitive color Doppler with a low velocity range (10–15 cm/s) shows ARSA as a vessel arising from the descending aorta at the level of the aortic isthmus and following an S-shaped course towards the right clavicle and shoulder (Figures 1b and c). This view has the advantage of providing visualization of the origin and course of the anomalous artery in the same plane. This view can also facilitate evaluation in cases in which the origin of ARSA is not in its most common position, such as ARSA originating anteriorly from the aortic arch or very distal to the left subclavian artery. It is important not to confuse ARSA with the azygos vein and its anastomosis with the superior vena cava. In the coronal view, the azygos vein courses parallel to the right side of the aorta, while ARSA arises from the aorta and follows an oblique course to reach the right arm. Pulsed Doppler interrogation is recommended to distinguish ARSA from the azygos vein in this region. In summary, fetal ARSA can be viewed in the coronal plane using ultrasonography. This approach shows both the anomalous origin of the artery and its S-shaped course to the right shoulder. Although the detection of ARSA is possible in a coronal view, it should be confirmed in the three vessels and trachea view. This work was supported by Fondo de Investigaciones Sanitarias (FIS# PI081712 and BA#09/90011). The authors are grateful to Mr David De León for assistance with graphics and to Mr Thomas O'Boyle for editorial assistance. J. De León-Luis*, C. Bravo*, F. Gámez*, L. Ortiz-Quintana*, * Fetal Medicine Unit, Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Calle O'Donnell, 48. 28009 Madrid, Spain