Definition

A vascular ring is a developmental abnormality of the primitive aortic arch in which the trachea and/or esophagus are surrounded by vascular and often ligamentous structures. Pulmonary sling, also known as anomalous left pulmonary artery, is a rare anomaly in which the lower trachea is partially surrounded by vascular structures.

The most common vascular rings are the double aortic arch, right aortic arch with aberrant left subclavian artery and left ligamentum arteriosus, left arch with aberrant right subclavian artery, and anomalous innominate artery.

Prevalence and Epidemiology

Vascular rings and slings represent approximately 1% of congenital cardiovascular anomalies,³ although this incidence may be underestimated because some lesions are asymptomatic. Most cases are sporadic, but there may be a genetic inheritance in some arch anomalies. Microdeletions of chromosome 22q11, in particular, have been associated with various arch anomalies.⁵

Etiology and Pathophysiology

Persistence of a segment of arch that should have regressed or regression of a segment that should have normally persisted explains the development of most arch anomalies. The theoretic embryonic double aortic arch model proposed by Edwards is most extensively used to demonstrate embryologic explanations for the variations in arch development.⁶ This model classifies vascular rings by the side of the ductus arteriosus and the site of dissolution of the double arches (Fig. 39-1).

FIGURE 39-1 Diagram of Edwards hypothetical double arch with bilateral ductus arteriosum. Breaks at 1 and 2 lead to left arch; breaks at 3 and 5 lead to right arch. A break at 1 with resorption of the right ductus results in normal anatomy. A break at 2 results in left arch with anomalous subclavian artery; typically, the right ductus resorbs (i.e., not a complete ring). A break at 4 results in right arch with mirror-image branching; the ductus courses from the innominate artery to the left pulmonary artery (not a complete ring). A break at 3 leads to right arch with aberrant subclavian artery; typically, the left ductus persists, coursing from the left subclavian to the left pulmonary artery and forming a vascular ring. A break at 5 differs in that the anomalous vessel is the innominate artery. AA, ascending aorta; DA, descending aorta; E, esophagus; LC, left carotid artery; LPA, left pulmonary artery; LS, left subclavian artery; PA, main pulmonary artery; RC, right carotid artery; RPA, right pulmonary artery; RS, right subclavian artery.

(Modified from Hernanz-Schulman M. Vascular rings: a practical approach to imaging diagnosis. Pediatr Radiol 2005; 35:961-979.)

Vascular rings may be complete (true) or incomplete (Fig. 39-2).³ In complete rings, the vascular structures entirely surround and compress the trachea and esophagus. These include the double aortic arch and right arch with aberrant retroesophageal left subclavian artery. In the double arch, an atretic segment of arch may complete the ring. With an aberrant left subclavian, a left ligamentum arteriosum connects the descending aorta and left pulmonary artery completing the ring.

FIGURE 39-2 Spectrum of common vascular anomalies. 1, Left arch with aberrant right subclavian artery (arrow). Order of arterial branching is right carotid, left carotid, left subclavian, right subclavian. 2, Anomalous right innominate artery (arrow). 3, Right arch mirror image. Order of arterial branching is left innominate, right carotid, right subclavian. 4, Right arch with aberrant left subclavian artery (arrow). Order of arterial branching is left carotid, right carotid, right subclavian, left subclavian. Arrowhead shows left ligamentum ductus arteriosum. 5, Double aortic arch. 6, Double arch with atretic segment (arrow).

(Courtesy of Dr. Robin Smithuis, Rijnland Hospital, Leiderdorp, the Netherlands.)

In incomplete rings, the vascular anomalies do not entirely encircle the trachea and esophagus, but do cause mass effect on these structures. These include the left arch with aberrant right subclavian artery and anomalous innominate artery.³ In the case of an aberrant right subclavian, the vessel itself or an aortic diverticulum (Kommerell diverticulum) at the takeoff of the artery compresses the posterior aspect of the esophagus. In anomalous innominate artery, the right innominate artery arises too far to the left from the arch and compresses the trachea anteriorly as it crosses the midline.

The mirror image right arch is a common vascular anomaly that comes to clinical attention because of associated cyanotic heart disease. It does not form a vascular ring and does not compress the trachea or esophagus.

Clinical Presentation

Symptoms vary with the tightness of the ring around the trachea and/or esophagus, and hence the degree of tracheobronchial compression. Tight rings usually manifest in neonates or infants. Symptoms include stridor, cough, repeated pulmonary infections, cyanosis, and respiratory failure, and feeding difficulties.^1–4 Looser rings may be discovered in older children or adults in whom mild dysphagia or choking on food prompts evaluation. Some asymptomatic rings will be discovered incidentally during an imaging study performed for other clinical indications. Rings that are asymptomatic early in life can become symptomatic later in life if the vascular structures become ectatic and compress the airway or esophagus.² Double aortic arches tend have more severe symptoms and present earlier than other rings.⁷ Slings commonly manifest in neonates, producing respiratory compromise.

Imaging Studies