The "full rectangle" sign: a novel method for ultrasonographic diagnosis of fetal aberrant right subclavian artery.

Objective: To evaluate the feasibility and accuracy of a novel ultrasonographic screening method for an aberrant right subclavian artery (ARSA) using the novel "full rectangle" method.

Methods: This prospective study was conducted at a tertiary care center, September 2022 to February 2023. The study included unselected pregnant women at 14-38 weeks of gestation referred for routine or targeted anomaly scans. All participants underwent scanning by two experienced sonographers to ascertain the presence or absence of aberrant right subclavian artery (ARSA) using both conventional and novel "full rectangle sign" methods for validation purposes. This is a novel screening method for ARSA that demonstrates the retro-tracheal course at the level of the supra-aortic vessels, forming what we term the "full rectangle sign".

Results: A cohort of 138 patients was enrolled. The "full rectangle" sign was discerned in 6 fetuses with ARSA (4.3%), while the typical three-sided figure of the right subclavian artery was demonstrated in the remaining 132 fetuses (95.7%). The novel method demonstrated 100% feasibility and complete concordance with the conventional method.

Conclusion: The study results indicate that the full rectangle sign serves as an effective and dependable screening tool for identifying ARSA. It offers the advantage of a clear, unobstructed view at a level unaffected by sternum shadowing and eliminates confusion with the azygous vein.