The most common form of vascular ring compression is PRAA with absence of the left arch. The intersegmentals are pulled forward along the aorta as usual but the left arch instead of the right arch separates from the dorsal aorta. Consequently, the right 4th aortic arch, left-sided ductus arteriosus and pulmonary artery form a vascular ring around the esophagus and trachea. The esophageal compression is relieved by dividing the ductus (or ligamentum arteriosum).

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In this surgical photograph of a dog with a simple PRAA the ligamentum arteriosum has been isolated and doubly ligated, and it will be divided between the ligatures. Sometimes the ligamentum is closed at the pulmonary artery but remains open into the aorta, therefore it is always wise to do a suture ligation at each end of the so-called ligamentum in case it is partially patent.

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After division of the ligamentum, the esophagus (E) is dissected free and expands in the area that was constricted.

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