A right ligamentum arteriosum is a remnant of the right caudal aortic arch.  It may co-exist with any of the other arch abnormalities and cause independent vascular ring compression of the esophagus.  Ventrally the right ligamentum attaches to the right pulmonary artery.  Dorsally it may attach directly to the aorta, to a retroesophageal right subclavian artery, or to an atretic or functional right 4th arch.  These can all be dissected from the dorsal aspect and separately ligated and divided if appropriate.