When does an aberrant right subclavian artery create a vascular ring?

OBJECTIVE: To describe the rare combination of findings where a left aortic arch and aberrant right subclavian artery are associated with a vascular ring, which is in the setting of a right-sided arterial duct. METHODS: Analysis of all prenatally diagnosed cases of left aortic arch and right-sided arterial duct (between 2016 and 2025) at three fetal cardiac centres (2 UK and 1 Austrian) with documentation of aortic arch branching pattern. RESULTS: In 5/6 cases, aberrant right subclavian artery was identified. Genetic abnormality was identified in 50% of cases (22q11 microdeletion). Three fetuses had a ventricular septal defects, and two cases had vascular abnormalities (with further characterisation on postnatal CT). No fetuses had extracardiac abnormalities. CONCLUSION: Left aortic arch with aberrant right subclavian artery is not uncommon in the general population but when associated with other abnormalities may also be a marker for chromosomal and genetic abnormalities. If not fully understood, patients may be incorrectly counselled regarding the likelihood of respiratory and swallowing symptoms of a vascular ring. An understanding of the circumstances in which a ring can arise is needed. Our study adds to the limited published data on this condition, with a view to improving clinician understanding and guiding accurate prenatal counselling.