Arch of aorta... or arches??
During early embryonic life, two dorsal aortae develop which run throughout the length of embryo. Later on, the caudal parts fuse to form a single thoracic/abdominal aorta. Of the remaining unfused aortae, the right one regresses and left one forms the primordial aorta. In case of double aortic arch, the right dorsal aorta persists. It is usally larger and passes posterior to trachea and esophagus, forming a vascular ring. Formation of this ring results in compression of these structures. Compression produces symptoms in early childhood like difficulty in breathing and characteristic inspiratory stridor. Severe airway obstruction may also lead to episodes of cyanosis. Adults may present more commonly with difficulty in swallowing rather than breathing as the tracheal development achieves completion. Image via: https://images.app.goo.gl/hYBE5ZJmZ55Visci9