Prenatal Echocardiographic Assessment of Right Aortic Arch

OBJECTIVES: To report our experience with fetal diagnosis of right aortic arch (RAA) variants based on the ductus arteriosus (DA) anatomy and brachiocephalic vessel branching pattern (BVBP) respectively to the trachea and to establish whether the echocardiographic "V-shaped" or "U-shaped" appearances of the fetal upper mediastinum were sufficiently accurate for fetal aortic arch (AA) assessment.

METHODS: We retrospectively identified patients with a fetal diagnosis of RAA referred to our tertiary center from 2011 to 2017 and selected those who had post-natal confirmation of AA anatomy. Prenatal and postnatal medical records, including echocardiographic and CT/MRI scan reports, were reviewed and cardiac and extracardiac abnormalities and the results of genetic testing were recorded.

RESULTS: Among 55 consecutive fetuses with a diagnosis of RAA, 6 patients were lost to follow-up, 1 pregnancy was interrupted and 3 patients were excluded for lack of post-natal confirmation. In the remaining 45 patients the AA anatomy was studied after birth by CT in 39, MRI in 1, and only by direct exploration at cardiac surgery in 5 patients. Fetal "U-shaped" appearance was found in 37/45 patients (82%) and all had a complete vascular ring (CVR). Of those, at post-natal confirmation, 21/37 patients (57%) had RAA with Kommerell diverticulum, left posterior ductus arteriosus (LPDA) and aberrant left subclavian artery (ALSA) (RAA/LPDA/ALSA), 11/37 patients (30%) double aortic arch (DAA), 4/37 patients (11%) RAA with Kommerell diverticulum, LPDA and mirror image (MI) branching (RAA/LPDA/MI), 1/37 patient (2%) RAA with Kommerell diverticulum, LPDA and aberrant innominate artery (ALIA) (RAA/LPDA/ALIA). Fetal "V-shaped" appearance was found in 3/45 patients (7%) and all had RAA with right DA (RDA) not forming a CVR and MI branching (RAA/RDA/MI). In 5/45 fetuses (11%) with neither "U-" nor "V-shaped" appearance a RAA with left anterior ductus arteriosus (LADA) arising from the left innominate artery (IA) and MI branching (RAA/LADA/MI) was found, not forming CVR. Twelve patients (12/45 - 27%) had a congenital heart defect (CHD), among which "RAA forming CVR" (fetal "U-shaped" appearance) was associated with septal defects in 6/37 (16%) while "RAA not forming CVR" (fetal "V-shaped" appearance or none) was associated with major CHD in 6/8 (75%).

CONCLUSIONS: We conclude that "V-shaped" appearance only means that the transverse AA and DA run together on the same side of the thorax (trachea) and "U-shaped" appearance is always the sign of a CVR. Among CVR, RAA/LPDA/MI is more frequent than previously described. Finally, "RAA forming CVR" is usually not associated with complex CHD, as opposed to "RAA not forming CVR". This article is protected by copyright. All rights reserved.