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.

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In 2 dogs a right-sided patent ductus arteriosus was discovered at surgery. In each dog, there was a normal left aortic arch, brachiocephalic trunk, and left subclavian artery. The esophagus was constricted by a large PDA running from the aorta to the pulmonary artery.

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