Vascular rings are anomalies of the thoracic vasculature in which vessels encircle and may compress structures near the aortic arch (i.e.- trachea, esophagus). â€śComplete vascular ringsâ€ť are abnormal vessels that form a complete circle around the trachea and esophagus. â€śIncomplete vascular ringsâ€ť are abnormal vessels that do not form a complete circle around the trachea and esophagus but compress the trachea and/or esophagus.
Vascular rings form during development of the aortic arch and the great vessels. The great vessels are derived from six pairs of primitive aortic arches (left and right pairs), one from each branchial cleft. There are also paired dorsal aortae which connect the sixth arch to the descending aorta, and intersegmental arteries which will form the left subclavian and distal right subclavian arteries. The six pairs of primitive arches are not present concurrently. They form and regress at different times. The first arches contribute to the external carotid arteries, the second arches contribute to the stapedial and hyoid arteries, the third arches form the common carotid arteries and proximal portions of the internal carotid arteries, the left fourth arch forms part of the left aortic arch whereas the right fourth arch forms part of the proximal right subclavian artery. The fifth arch regresses, and the sixth arch forms part of the pulmonary arteries with the left sixth arch forming the left ductus arteriosus and the right arch regressing. The paired dorsal aortae connect the pulmonary ductus to the descending aorta, with the right dorsal aorta regressing completely to leave behind the left aortic arch. Vascular ring malformations cause different abnormalities depending on which portion of the primitive arch is involved.
The most common vascular ring is a double aortic arch (40%), in which there is failure of regression of the right fourth branchial arch with persistence of the left fourth branchial arch and connection of the left and right branchial arches behind the esophagus to form the descending aorta. This results in a complete circle around the trachea and esophagus and compression of these structures.
The second most common vascular ring, a right aortic arch with left ligamentum arteriosum (30%), is due to failure of regression of the right fourth branchial arch but with regression of the left fourth branchial arch. Variations included in this model are a retroesophageal left subclavian artery branching from the descending aorta with a left ligamentum arteriosum connecting the descending aorta to the left pulmonary artery (completing the vascular ring), as well as mirror image branching.
The actual prevalence of vascular ring malformations is unknown however many cases likely go unreported as patients are not always symptomatic. Statistically 1-3% of reported congenital cardiovascular anomolies are vascular rings. Associated cardiovascular aortic arch anomolies may include Tetrology of Fallot, ventricular septal defect, coarctation of the aorta, transposition of the great vessels, and chromosome band 22q11 deletions.
Vascular rings are symptomatic when they compress structures inside the ring. Double aortic arch symptoms usually present in the newborn period. Right sided aortic arch with aberrant left subclavian artery and ligamentum arteriosum patients are often asymptomatic in early life unless the ligamentum arteriosum is relatively short. With a short ligamentum arteriosum, the ring may be small and become symptomatic in the first few weeks of life. More often with the right arch/aberant left subclavian type, symptoms only develop when the aorta and left subclavian artery become large compressing on the esophagus and cause feeding difficulties.
Stridor, due to airway compression, is the most common presenting symptom. Dyspnea and barking cough are less frequent. Patients may have a history of arching their back and extending their neck to decrease tracheal narrowing. Older children may have a history of recurrent respiratory infections, chronic cough, or wheezing which has been misdiagnosed as asthma. Patients may also have feeding difficulty with failure to thrive, vomiting, choking, and dysphagia. Physical exam may reveal wheezing and coarse respiratory sounds; however, physical exam may be entirely normal
The diagnosis of a vascular ring requires a high index of suspicion. Plain films may show a right-sided aortic arch (with or without a left sided aortic arch), leftward deviation of the trachea (especially on AP projection), and compression of the trachea (especially on the lateral view). Barium contrast esophogram may reveal posterior compression of the esophogus. Bronchoscopy can demonstrate non-specific external compression of the trachea. Echocardiography may be helpful in demonstrating nonspecific external compression of the airway. Magnetic resonance angiography and computed tomography angiography are exceptional in defining the relevant vasculature and visualizing the relationships with other mediastinal structures.
The only definitive treatment for vascular rings is surgical. If the patient is asymptomatic, watchful waiting is appropriate. However, if the patient is symptomatic (i.e.- stridor, dysphagia), surgery is indicated. For a double aortic arch, the smaller of the two arches is divided along with any other vascular structures making up the ring. In patients with a right-sided aortic arch with aberrant left subclavian artery and left ligamentum arteriosum, the ligamentum arteriosum is divided, thereby freeing the trachea and esophagus and interrupting the ring.