Vascular Rings 

Vascular rings are unusual congenital anomalies that occur early in the development of the aortic arch and great vessels. The primary symptomatology associated with vascular rings relates to the structures that are encircled by the ring, chiefly the trachea, and esophagus. Prompt diagnosis and treatment of these congenital abnormalities can be lifesaving.

The first vascular ring described was a double aortic arch noted by Hommel in 1737. Bayford reported retroesophageal right subclavian artery in 1794 after performing an autopsy on a woman who had experienced dysphagia for years and died of starvation. Maude Abbott described 5 cases of double aortic arch in 1932 and made the suggestion that surgical intervention should be undertaken in such cases. Finally, in 1945, Gross used the term vascular ring in the New England Journal of Medicine publication that he wrote after performing the first successful division of a double aortic arch. Since that time, numerous reports of successful treatment have occurred, and the forms of aortic arch anomalies causing this problem have been well delineated.

A vascular ring is a congenital condition in which the anomalous configuration of the arch and/or associated vessels surrounds the trachea and esophagus, forming a complete or incomplete ring around them. Several other related vascular anomalies involving arch vessels do not form a complete ring but have been grouped descriptively with vascular rings because they produce similar symptoms related to compression of the trachea and/or esophagus. Both complete and incomplete rings are discussed in this article.

Frequency

Vascular rings are uncommon anomalies and make up less than 1% of all congenital cardiac defects. They occur with about equal frequency in both sexes. No geographical or racial predominance exists. Some vascular rings are associated with other congenital heart defects; others may be isolated deficits.

The 2 most common types of complete vascular rings are double aortic arch and right aortic arch with left ligamentum arteriosum. These make up 85-95% of the cases.^{[1, 2, 3]}

Two other complete vascular rings that are extremely rare (< 1%) include (1) right aortic arch with mirror-image branching and (2) left ligamentum arteriosum and left aortic arch with retroesophageal right subclavian artery, right-sided descending aorta, and right ligamentum arteriosum.

Other named anomalies that produce symptoms but do not form a complete anatomic vascular ring make up the remainder and include the abnormally placed or anomalous innominate artery and the retroesophageal right subclavian artery with left-sided aorta and left ligamentum arteriosum.

The anomalous left pulmonary artery or pulmonary artery sling makes up about 10% of cases, although the exact number is difficult to determine because there are so few case reports.^[4] Although the pulmonary artery sling is not associated with the aortic arch or its branches, it arises from an abnormality of the sixth branchial arch and produces a complete ring. This anomaly is associated with intracardiac defects in 10-15% of cases.

The various forms of this anomaly occur very early in embryologic development. They result from the abnormal or incomplete regression of 1 of the 6 embryonic branchial arches. Several recent papers report the close association of band 22q11 deletion with anomalies of the aortic arch as well as other congenital cardiac abnormalities.^[5]

Early in normal development, both a dorsal and a ventral aortic arch are present. The 2 arches are connected by 6 embryonic branchial arches, as depicted in the image below. The third, fourth, and sixth embryonic arches are the most crucial in the development of the aortic arch and several of its major branches, as well as the ductus arteriosus and the main pulmonary arteries.

In normal development, each primitive arch either progresses into a functional vascular structure or involutes as follows:

• The right and left first and second arches become a portion of the arterial supply to the face.
• The third arches develop into the carotid arteries.
• The dorsal aorta between the third and fourth arches involutes.
• The fourth arches are the primary contributors to the aortic arch itself, with the proximal right fourth arch developing into the proximal right subclavian artery. The distal portion of the right fourth arch involutes at the point where it joins the dorsal arch. The left fourth arch remains as the aortic arch in normal development.
• The fifth arches involute bilaterally.
• The ventral right sixth arch becomes the proximal right pulmonary artery. The ventral portion of the left sixth arch develops into the left pulmonary artery, while the dorsal portion becomes the ductus arteriosus.
• The entire left and the distal right subclavian arteries arise from the seventh segmental arterial branches of the dorsal aorta.

Abnormal arch development results when one or more of the necessary involutions or other changes in embryonic arch structures does not occur.

Double aortic arch

The classic double aortic arch anatomy (see image below) develops when involution of the distal right fourth arch does not take place. The fourth right and left arches both persist and join the left-sided descending thoracic aorta. The right and left aortic arches encircle the trachea and esophagus. In about 30% of cases of double aortic arch, the small, or less dominant, of the arches is atretic but remains in continuity with the descending aorta, maintaining the complete ring. The double aortic arch forms a ring around the trachea and esophagus, compressing both of these structures. Tracheoesophageal compression typically results in early symptoms. This type of defect is rarely associated with intracardiac defects.

Right aortic arch – associated abnormalities

In cases of individuals in whom the left fourth branchial arch involutes and the right remains, a right aortic arch is present. Right aortic arch occurs less frequently than 1 in 100,000 times in the general population and may exist in the absence of any other anomalies. Its presence is suggestive of the existence of an associated anomaly. About 30% of patients with tetralogy of Fallot have an associated right aortic arch.

Persistence of the right arch with involution of the left creates a situation in which the origins of the left subclavian artery and ductus arteriosus can vary. Several of these configurations can produce a vascular ring.

Right aortic arch with aberrant left subclavian artery and left ligamentum arteriosum

In this anomaly, the right arch first gives off the left carotid artery, which travels anterior to the trachea (see image below). It then gives off the right carotid, followed by the right subclavian artery, and, lastly, the left subclavian artery, which courses in a retroesophageal position and gives rise to the ligamentum arteriosum from its base. The ligamentum arteriosum connects the left subclavian or descending aorta to the left pulmonary artery. The trachea and esophagus are surrounded by the ascending aorta anteriorly, the aortic arch on the right, the descending aorta posteriorly, and the ligamentum arteriosum and left pulmonary artery on the left. Almost 10% of these defects are associated with an intracardiac defect.

Right aortic arch with mirror-image branching and retroesophageal ligamentum arteriosum

In these cases, only partial resorption of the distal left fourth arch occurs. The first brachiocephalic vessel originating from the right arch is the left innominate artery, which, in turn, branches into a left carotid and left subclavian artery. These vessels course anterior to the trachea.

Following these, a right carotid artery and then a right subclavian artery arise. The ligamentum arteriosum is the final structure arising from the arch in this sequence. It originates from an area called Kommerell diverticulum, which represents the nonresorbed remnant of the left fourth arch and is situated at the point of merger between the right arch and the proximal descending thoracic aorta. The ligamentum passes leftward and behind the esophagus and then travels anteriorly to join with the left pulmonary artery and complete the ring, as depicted in the image below. More commonly, in cases of right aortic arch with mirror-image branching, the ligamentum arteriosum travels from the mirror-image innominate or left subclavian artery to the left pulmonary artery. A complete ring is not present in these cases. This type of vascular ring has a more than 90% association with intracardiac defects.

Vascular rings associated with left aortic arch

Two extremely rare complete rings occur in the presence of a left aortic arch, and both are associated with a right-sided descending thoracic aorta.

Left aortic arch with right descending aorta and right ligamentum arteriosum

The first arch vessel to exit the left aortic arch is the right common carotid, which passes anterior to the trachea. The left carotid is next, followed by the left subclavian artery. The right subclavian artery arises more distally as a branch of the proximal right-sided descending aorta. The ligamentum arteriosum arises from the base of the right subclavian artery or a nearby diverticulum and travels to the right pulmonary artery (see image below).

Left aortic arch, right descending aorta, and atretic right aortic arch

The brachiocephalic vessels arise from the left-sided arch in a normal arrangement. The left arch passes behind the esophagus to join a right-sided descending aorta. An atretic right arch is present and completes the ring.

Arch abnormalities producing compression symptoms without an anatomic ring

Anomalous innominate artery

The actual prevalence of this abnormality is widely debated. This is because, in as many as 90% of cases in which symptomatic tracheal compression is produced by the innominate artery, the vessel is noted angiographically to have a normal origin from the aorta. When an anatomic abnormality is noted in these cases, the innominate artery appears to originate from a more distal and leftward position on the arch than normal. As it takes its course from left to right, it crosses the trachea anteriorly and in doing so may produce compression of the trachea.

Retroesophageal right subclavian artery with left aortic arch and left ligamentum arteriosum

This is the most common of the arch vessel anomalies, occurring in about 0.5% of the population. In these cases, the right subclavian artery does not arise from an innominate trunk with the right carotid artery but originates as the last brachiocephalic branch from the descending aorta and takes a retroesophageal route to its destination, as depicted in the image below. A normally positioned ligamentum arteriosum is present on the left. If a right ligamentum arteriosum were present instead of one on the left, its course would proceed from the base of this anomalous right subclavian artery to the right pulmonary artery and a complete ring would exist. Instead, no true vascular ring is present in these cases. Most patients are symptomatic, but the occasional patient may present with dysphagia.

Anomalous left pulmonary artery or pulmonary sling

This abnormality occurs when the left main pulmonary artery arises as a branch of the right pulmonary artery instead of originating from the main pulmonary artery. This is believed to be an abnormality related to sixth aortic arch development. In this anomaly, the left pulmonary artery leaves the right and courses in a position cephalad to the right mainstem bronchus, proceeding around the right side of the trachea (see image below). It then travels between the trachea and esophagus as it goes to the left lung.

This lesion is often associated with hypoplasia and other abnormalities of the tracheal and bronchial cartilages. Most patients are symptomatic by 1 month after birth. Respiratory symptoms predominate, as the most severe compression is on the trachea. More than 50% of infants also have severe tracheobronchial anomalies such as tracheomalacia, stenosis, webs, or complete tracheal rings. Intracardiac defects are also seen in 20% of these infants.

In spite of the significant variability in this group of structural abnormalities of the aortic arch, they all possess a common feature. They all produce some degree of compression on the major airway structures and/or the esophagus. The location and severity of compression varies with the configuration of the lesion. Individuals with anomalies producing more severe compression are likely to present earlier in life.

Tracheal or tracheobronchial malacia and stenosis may develop in association with some of these lesions in the areas where the greatest degree of compression exists. This is particularly true in cases of anomalous left pulmonary artery.

Other congenital cardiac anomalies may be present in association with aortic arch anomalies.

The presence of a right aortic arch should always raise the suspicion of additional congenital cardiac disease. Right aortic arch has been reported in as many as 34% of cases of tetralogy of Fallot. Other intracardiac lesions found in association with a right aortic arch include double-outlet right ventricle, truncus arteriosus, ventricular septal defect with pulmonary atresia, transposition of the great vessels, tricuspid atresia, and absent left pulmonary artery.

Anomalous left pulmonary artery has also been associated with other cardiac defects in as many as 50% of cases. These include the aforementioned lesions as well as persistent left superior vena cava, atrial septal defect, and ventricular defect. Complete tracheal rings (congenital absence of the membranous trachea) resulting in tracheal stenosis are another anomaly reported in as many as 50% of infants with anomalous left pulmonary artery. The combination of these 2 lesions is often termed the ring-sling complex.

Symptoms and physical findings produced by vascular rings are primarily those of airway or esophageal compression. Individuals with a narrow or tight ring have a significant degree of constriction of one or both of these structures and present very early in life.

The vast majority of patients with a vascular ring present with symptoms in infancy or very early in childhood.^[6] However, a small number of patients do not manifest symptoms until later in life, and others remain entirely asymptomatic.^[7] Common symptoms include stridor, cyanosis, wheezing, respiratory distress, apnea, and/or a characteristic high-pitched, brassy cough. Additional findings include a history of asthma, recurrent pneumonia, or evidence of dysphagia or difficulty with feedings. In some cases, airway symptoms are worsened or aggravated by feedings. Intercostal retractions during respiration are observed in some infants with severe obstruction. Others may try to maintain a position in which the head is hyperextended to improve breathing and minimize the obstruction. Air-trapping and evidence of pulmonary hyperinflation may also be present in one or both lungs in severe cases.

Symptoms of airway obstruction predominate in patients who present in infancy or the first few years of life. Dysphagia and symptoms related to the esophagus are the more likely presenting findings in older children and adults with vascular rings. Esophageal compression is usually posterior. Symptoms that are present soon after birth may include slow breast or bottle feeding, fatigue with feeding, frequent regurgitation, and aspiration pneumonias. In most cases, workup is initiated when solid foods are introduced, which causes more pronounced dysphagia.

The double aortic arch is the anomaly that usually produces the most severe airway compression in the youngest patients. The second most common configuration, right aortic arch and left ligamentum arteriosum with retroesophageal left subclavian artery, displays a spectrum of severity. Some individuals present in infancy or very early in childhood while others do not present until adulthood.

Although patients with associated cardiac lesions may have additional symptoms secondary to that abnormality, symptoms of airway compression related to the constricting vascular ring are usually most prominent.

Finally, note that some patients with a complete vascular ring have minimal symptoms or remain asymptomatic. In such cases, the abnormal arch anatomy is often discovered incidentally when the patient is undergoing diagnostic studies for another problem.

Conversely, if left aortic arch with associated retroesophageal right subclavian artery is incidentally found during diagnostic studies for symptoms of dysphagia, the clinician should not believe that this vascular abnormality, which is not a true vascular ring, is the source of the symptoms. Additional investigation for the true cause should be pursued. This arch abnormality, previously believed to be responsible for dysphagia symptoms and for which the term dysphagia lusoria was coined long ago, is rarely responsible for esophageal symptoms.

Surgical division of a vascular ring is indicated in all symptomatic patients. To avoid serious complications such as sudden death or significant tracheal or bronchial damage, surgery should not be delayed, especially in patients with symptoms of airway compression.

Double aortic arch

Visualization through a left thoracotomy incision shows a normally positioned left, or anterior, arch exiting the pericardium and joining the left-sided descending thoracic aorta after giving off the left subclavian artery. The ligament arteriosum is positioned normally. The posterior, or right, arch joins the descending thoracic aorta at the same level as the anterior arch but reaches that point from an extreme posterior course behind the esophagus. Often, the posterior arch is visible only after circumferential dissection of the aorta at the level of its junction with the anterior arch.

Right aortic arch with retroesophageal left subclavian artery and left ligamentum arteriosum

The arch travels to the right and behind the esophagus, joining the left-sided descending aorta. As it takes this course, it gives off the left carotid artery first. Then, it sequentially gives off the right carotid, the right subclavian, and the left subclavian arteries. This last branch often has a retroesophageal position. The ligamentum arteriosum courses from the base of the left subclavian artery to the left pulmonary artery.

Through a left thoracotomy, the structures visible in normal position are the descending thoracic aorta and the distal portion of the left subclavian artery. These structures can be traced proximally to identify the site where the left subclavian artery exits the right arch as it joins with the descending aorta. The ligamentum arteriosum can be found at the base of the subclavian artery and traced towards the pulmonary artery.

Right aortic arch with mirror-image branching and retroesophageal ligamentum arteriosum

In the rightward and retroesophageal course, the aortic arch gives off a left innominate artery, which in turn branches into the left carotid and subclavian arteries. The right carotid artery then branches from the arch, followed by the right subclavian. The ligamentum arteriosum exits distal to this point from the area of Kommerell diverticulum and courses to the left pulmonary artery. As viewed through a left thoracotomy, the descending thoracic aorta is visible and can be traced proximally to the area of its merger with the right aortic arch, which joins it from behind the esophagus. In this area, the ductus diverticulum and ligamentum arteriosum can be found.

Left aortic arch with right descending thoracic aorta and right ligamentum arteriosum

The arrangement of this anomaly is the mirror image of right aortic arch with retroesophageal left subclavian artery and left ligamentum arteriosum. Approaching through a right thoracotomy, structures are identified and traced in the same manner.

Left aortic arch with right descending aorta and atretic right arch

In a retroesophageal position, the left arch passes to the left of the trachea to join the right descending thoracic aorta. The surgical view is via right thoracotomy. At the level of this junction and immediately superior to a right ligamentum arteriosum, an atretic right arch is found. The brachiocephalic vessels in this case exit the left arch in a normal sequence.

Anomalous innominate artery

The brachiocephalic vessels exit the left arch in the normal sequence. The innominate artery may be more distally positioned and leftward on the arch than normal.

Retroesophageal right subclavian artery with left aortic arch and left ligamentum arteriosum

Rather than an innominate artery exiting the arch as the normal first brachiocephalic branch, the right carotid is the first brachiocephalic vessel. It is followed by the left carotid and then the left subclavian artery. The right subclavian artery is the last brachiocephalic branch to exit the arch, and it takes a course rightward and posterior to the esophagus. The ligamentum arteriosum is normally positioned on the left.

Anomalous left pulmonary artery

Instead of the normal pulmonary artery configuration in which the main pulmonary artery gives rise to both the right and left pulmonary arteries, the main pulmonary artery continues behind the ascending aorta and rightward as the right pulmonary artery, which then gives off the left pulmonary artery. The left pulmonary artery passes from right to left between the trachea and esophagus in its course to the left lung. The ligamentum arteriosum takes a course from the junction of the main and right pulmonary arteries posteriorly to the aorta.

Individuals who are asymptomatic from a vascular ring may not require surgical intervention.

In patients with vague symptoms of difficulty swallowing, the clinician should not regard the presence of a left aortic arch with retroesophageal right subclavian artery as the definitive cause of the patient's symptoms. Reports of surgical division of anomalous retroesophageal right subclavian artery for treatment of such symptoms appear in older surgical literature. This was found to be ineffective treatment because the majority of these patients continued to have symptoms. Currently, the presence of this anomaly is believed not to cause such symptoms, and the clinician should continue further diagnostic studies.

Cases of anomalous innominate artery with evidence of tracheal compression do not require surgical treatment if the patient has few or no symptoms. Only about 10% of these patients require surgery.