A vascular ring is a type of congenital lesion where abnormally located normal vessels may cause compression or obstruction of the esophagus or airway.
These arteries may be those carrying blood to the body, to the lungs, or both. They are most easily segregated into three main groups: vascular rings, the innominate compression syndrome, and pulmonary arterial slings.
Vascular rings include a number of anatomic variations of abnormal development of the aortic arch complex resulting in the formation of a ring encircling both the trachea and esophagus.
The aorta originally develops as a series of arches with bilateral symmetry. By the end of the second month of fetal development, parts of the arch complex have regressed leaving the "typical" anatomy of a left aortic arch with three arch branches (innominate, left common carotid and left subclavian) and a left-sided ductus arteriosus from the proximal left pulmonary artery to the aorta in the general vicinity of the left subclavian artery origin.
Virtually all vascular rings can be explained by abnormal regression or persistence of different components of the bilateral aortic arch complex.
The two most common anatomic variants of true vascular rings, occurring in nearly equal frequency, are persistent double aortic arch and right aortic arch with anomalous origin of the left subclavian artery.
In the latter, the left-sided ligamentum arteriosum completes the vascular ring as it passes from the left pulmonary artery to the left subclavian artery as it travels abnormally behind the esophagus.