Discussion

Aortic arch anomalies are explained by the Edwards hypothetic double aortic arch in which selective regression of various parts of either arch demonstrates various arch anomalies. ^{Reference Crawford1} Such anomalies may occur via interruptions at two sites in the double aortic arch: in the left posterior arch distal to the ductus and the left anterior arch proximal to the left common carotid artery. ^{Reference Fong and Venables2} However, few reports have described prenatally diagnosed left-sided isolated innominate arteries. ^{Reference Li, Zhang, Yan and Pei3,Reference Hao, Zhang and Zhao4} The root of the left-sided innominate artery may be narrowed or occluded to various degrees after birth due to regression of the left ductus arteriosus originating from the left sixth arch. ^{Reference Park5} However, most cases are asymptomatic, with mild symptoms, such as a weakened peripheral pulse in the left upper limb due to mild ischaemia of the left subclavian artery. ^{Reference Gowda, Bhat, Jayaranganath and Hegde6} Immediately after ductus arteriosus regression, the circulation of the left extremity is compensated by retrograde flow from the left vertebral artery. Subsequently, the blood supply from the internal thoracic and intercostal arteries via the collaterals gradually increases, replacing the supply from the vertebral artery. However, a small number of cases have been reported wherein cerebral atrophy or vertebrobasilar artery insufficiency developed during infancy or later due to a substantial amount of blood diversion from the vertebral artery to the subclavian artery, requiring revascularization surgery. ^{Reference Gowda, Bhat, Jayaranganath and Hegde6–Reference Le Bret, Leobon and Roubertie8}

The decision to perform surgery before symptom onset remains uncertain, given that the accurate prevalence of symptomatic patients with this rare condition is unclear. Based on previous reports describing most patients as asymptomatic, we decided to monitor our patient symptom onset. Since some cases have been reported to develop the symptoms during adulthood, lifelong follow-up might be required. ^{Reference Li, Zhang, Yan and Pei3} The accuracy of prenatal diagnosis is steadily improving, and the prenatal diagnosis of such a condition, as in this case report, could enable us to observe the patients prospectively. This approach may assist in elucidating the accurate prevalence and clinical features in symptomatic patients and provide insights into a better clinical decision-making process. In this case, our initial observation focused on the right aortic arch and right ductus arteriosus, and subsequent exploration, guided by the knowledge that 98% of these patients could have another cardiac anomaly, enabled us to find an isolated left-sided innominate artery. ^{Reference Maier and Van der Woude9}

In conclusion, in cases of an isolated left-sided innominate artery, occlusion or stenosis of the innominate artery root associated with closure of the ductus arteriosus after birth could be tolerated. However, follow-up should be performed by paying attention to upper limb weakness and central nervous system complications.