A vascular ring is a type of congenital lesion where abnormally located blood 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
- 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.
The symptoms seen with vascular rings can be quite varied. Many patients are asymptomatic or have very mild symptoms. They may occasionally be noted in the newborn, but more often are recognized later. Vascular rings diagnosed in patients less than six months of age are often associated with symptoms of airway obstruction, such as stridor (noisy breathing). Worsening of breathing difficulties with feeding or during upper respiratory infections may be seen.
Children with double aortic arch anomalies tend to present earlier than those with right aortic arch variants. Swallowing problems are uncommon in the first months of life while children are on a liquid diet. Choking or swallowing difficulties are more common in older children as the predominant symptoms. Occasionally, a vascular ring is discovered incidentally during evaluation of a seemingly unrelated problem.
Physical examination may help characterize the “noisy breathing” and help differentiate it from other more common problems such as asthma. With a vascular ring, the noisy breathing may be heard both during inspiration and expiration, while in asthma, the noise is mainly at the end of expiration.
Occasionally, physical examination will detect an abnormally weak pulse in an arm or the legs due to narrowing in a part of the anomalous blood vessels. Listening to the chest for murmurs is often included to assess the need for more thorough evaluation for associated cardiac anomalies (which are uncommon).
A chest X-ray is often performed as a part of the initial evaluation, and if the aortic arch appears to be right-sided, a vascular ring should be suspected. The identification of the side of the aortic arch on the plain chest x-ray, though, may be difficult in some children, particularly infants.
Patients with swallowing difficulties should undergo a barium swallow as part of the initial evaluation. This will typically demonstrate abnormal compression of the middle part of the esophagus, characteristic for a vascular ring. A barium study demonstrating classic features of a vascular ring, coupled with a chest x-ray showing a right-sided aortic arch is generally all that is necessary to proceed with operation.
When breathing symptoms predominate, bronchoscopy may be performed which will often demonstrate extrinsic, sometime pulsatile compression of the trachea.
An operation to divide the vascular ring is indicated in all symptomatic cases. Given the low risk associated with surgical division of a vascular ring, it is difficult to recommend continued observation, particularly in younger patients.
The goal of surgical intervention for vascular rings is to convert a restrictive, closed ring into one that is open realizing that there may still be an abnormal course of some of the blood vessels. With the ring open in at least one direction, symptoms related to esophageal and tracheal compression will be relieved.
In most cases the operation is performed using an incision on the left side of the chest, entering between the ribs. In the case of double aortic arch, the left side of the ring (which is usually the smaller side) is divided where it is compressing the esophagus.
With a right aortic arch and anomalous left subclavian artery, the ligamentum arteriosum (a ligament that was a blood vessel during fetal life) is divided between the descending aorta and the pulmonary artery. Hospitalization after surgery is rarely more than a day or two.
Complete relief of symptoms may be noted immediately following the operation, although persistence of some findings is not uncommon. In infants, there may be some degree of tracheomalacia (floppiness of the trachea) associated with the vascular anomaly and persistence of some stridor, particularly during times of great activity or during upper respiratory infections.
Depending on the specific anatomy, division of the ring may still leave either the subclavian artery or a segment of the aorta itself in an abnormal position behind the esophagus. Improvement of swallowing symptoms in such cases may be seen only gradually.