Aortic Surgery by Mike Poullis

Vascular Ring, Right Aortic Arch

INTRODUCTION

Background: Several types of vascular rings exist in which the aortic arch is right sided. Although the specific anatomic details of the various forms differ, they share the defining feature of all vascular rings, namely, encirclement of the trachea and esophagus by connected segments of the aortic arch and its branches. A right aortic arch may occur without forming a vascular ring. The presence or absence of a vascular ring in the setting of a right aortic arch depends on the branching of the brachiocephalic vessels and the location of the ductus arteriosus, as discussed below.

Embryology

The simplest way to understand the anatomy and development of vascular rings with a right aortic arch is to begin by considering the bilateral system of pharyngeal arch vessels in the early embryo.

Early in the course of embryonic morphogenesis, 6 pairs of pharyngeal arch arteries develop in conjunction with the branchial pouches. The first through sixth arches appear in more or less sequential fashion, with left-right symmetry, and constitute the primitive vascular supply to the brachiocephalic structures, running from the aortic sac to the paired dorsal aortas. As normal cardiovascular morphogenesis proceeds, a patterned regression and persistence of the various arches and right-sided dorsal aorta occur, ultimately resulting in the mature configuration of the thoracic aorta and its branches. The third, fourth, and sixth arches, along with the seventh intersegmental arteries and the left dorsal aorta, are the primary contributors to the normal aortic arch and its major thoracic branches (see Image 1).

The segments of the bilateral aortic arch system that normally regress include the distal portion of the sixth arch and the right-sided dorsal aorta. Normally, the left fourth arch becomes the aortic arch, the right fourth arch contributes to the innominate artery, the distal left sixth arch becomes the ductus arteriosus, the proximal sixth arches bilaterally contribute to the proximal branch pulmonary arteries, the left dorsal aorta becomes the descending thoracic aorta, and the dorsal intersegmental arteries bilaterally become the subclavian arteries. Vascular rings are formed when this process of regression and persistence does not occur normally, and the resulting vascular anatomy completely encircles the trachea and esophagus. (Other forms of aortic arch anomaly occur in which a vascular ring is not present.) A right aortic arch is formed when the right dorsal aorta remains patent and either the left fourth arch or the left dorsal aorta regress abnormally (see Images 2-3).

Anatomy

Two primary forms of vascular ring with a right aortic arch exist, and 2 other forms are much less common.

In the most frequent form of vascular ring with a right aortic arch, an aberrant origin of the left subclavian artery from a retroesophageal diverticulum (diverticulum of Kommerell) is present, which originates as the last branch of the aortic arch (distal to the right subclavian artery). The ring is completed by a left-sided ductus arteriosus (or its remnant ligamentum arteriosum) passing from the aberrant left subclavian artery to the proximal left pulmonary artery (see Image 2). The retroesophageal diverticulum is distinguished from the aberrant left subclavian artery by its larger caliber. Although the course of the descending thoracic aorta varies, it typically crosses gradually to the left of the vertebral column to pass through the diaphragm in the usual location of the aortic hiatus.
In the second major type of vascular ring with a right aortic arch, the brachiocephalic vessels originate from the arch in mirror-image fashion with the left innominate artery the first branch followed by the right common carotid and subclavian arteries. A left-sided ductus arteriosus or ligamentum arteriosum passes between the descending aorta and the proximal left pulmonary artery (see Image 3). In contrast to right aortic arch with aberrant left subclavian artery from a retroesophageal diverticulum, the descending aorta usually crosses to the left side of midline proximally in its course, although in rare cases, it remains to the right of midline until reaching the lower portion of the thorax.
A rare form of vascular ring with a right aortic arch is a right arch with an aberrant retroesophageal innominate artery arising as the last branch of the arch and then giving off a ductus/ligamentum to the proximal left pulmonary artery (see Image 4). With this form of vascular ring, the retroesophageal innominate artery does not arise from a diverticulum.
An uncommon form of right aortic arch that technically is not a vascular ring but may cause symptoms similar to a ring is a right arch with an aberrant left subclavian artery arising as the last branch of the arch and a left-sided descending aorta. The ductus arteriosus is right sided; thus, a ring is not actually formed, but the retroesophageal descending aorta may rarely cause symptomatic airway symptoms, esophageal symptoms, or both.

Associated cardiovascular anomalies

Vascular rings, including those with a right aortic arch, usually occur without associated cardiovascular anomalies. Ventricular septal defect is the most common associated anomaly, although various others have been reported as well.

Associated syndromes and noncardiac conditions

Vascular ring with a right aortic arch is associated with a band 22q11 deletion in approximately 20% of patients (see Causes). Band 22q11 deletion is responsible for DiGeorge, velocardiofacial, and conotruncal anomaly face syndromes, which are often referred to by the unified terms CATCH-22 syndrome or chromosome 22q11 deletion syndrome. In patients with vascular rings, the frequency of phenotypes satisfying the clinical criteria for these various syndromes is not known. The important point, rather, is that vascular rings with a right aortic arch may be associated with band 22q11 deletion, which has a variety of other possible manifestations. These include, but are not limited to, palatal abnormalities, laryngotracheal anomalies, speech and learning delay, characteristic facial features, hypocalcemia, abnormalities of T-cell–mediated immune function, and neurologic defects.

Occasionally, patients with right aortic arch may have anomalies consistent with either VACTERL (vertebral, anal, cardiac, tracheal, esophageal, renal, limb) or CHARGE (posterior coloboma, heart defect, choanal atresia, retardation, genital, ear) associations. One of the more important noncardiac features that is sometimes found in association with right aortic arch is esophageal atresia, insofar as an undiagnosed arch anomaly may complicate repair of the esophageal atresia, which is usually recognized earlier than the right aortic arch.

Pathophysiology: Vascular rings, by definition, encircle the trachea and esophagus, usually causing compression of both structures. Compression of the trachea causes upper airway obstruction that impairs inspiratory and, to a lesser degree, expiratory airflow. The extent of respiratory impairment depends upon the severity of compression, which can vary considerably. Symptomatic compression of the trachea seems to occur slightly later in life with vascular rings having a right aortic arch when compared to vascular rings with double aortic arch.

In addition to airway symptoms, patients may experience swallowing problems related to esophageal compression. These typically manifest as vomiting and feeding intolerance in infants and younger children and as dysphagia later in life. Swallowing dysfunction may contribute to respiratory symptoms as a result of aspiration and/or compression or irritation of the membranous portion of the trachea as a food bolus traverses the area of esophageal obstruction. Although respiratory or esophageal pathophysiology may predominate in any given patient, respiratory compromise generally is more problematic in younger patients. Those with primarily esophageal symptomatology tend to be older at presentation. The pathophysiology of vascular rings with a right aortic arch does not differ among the various anatomic forms.

Frequency:

In the US: The incidence of right aortic arch and vascular rings in general is not known, although vascular rings comprise an estimated 1% of cardiovascular malformations managed surgically.

Mortality/Morbidity:

The natural history of vascular rings in general, including those with a right aortic arch, is not well defined. Vascular rings were among the first congenital cardiovascular anomalies repaired surgically, and surgical management has been the standard of care for more than 50 years. Patients with significant airway compression may die as a result of respiratory compromise, but such events are rare.

Preoperative morbidity is generally limited to respiratory symptoms, feeding problems, or both. Some patients may develop recurrent respiratory infections, and some may exhibit failure to thrive because of the combination of increased metabolic requirements from respiratory and feeding work and relatively poor oral intake.

Race: Based on limited data, no racial predilection is apparent.

Sex: No sex predilection of vascular rings with right aortic arch has been documented.

Age: A right aortic arch is a developmental abnormality that is present in the fetus. The postnatal age at which this anomaly is identified may vary, although most patients are identified in early infancy.

CLINICAL

History: The history of patients with right aortic arch and vascular ring depends on several factors, including the severity of tracheal compression, esophageal compression, or both and whether associated anomalies are present.

Among patients with a vascular ring, those with right aortic arch tend to present slightly later than those with a double aortic arch, but this is a minor difference and is not a reliable distinguishing feature. The classic history of a patient with a vascular ring is noisy breathing noted by the parents during the first few weeks of life.

Young patients may have experienced episodes often referred to as apparent life-threatening events (ALTE) or “death spells,” in which they experience acute apneic or severe obstructive events accompanied by cyanosis. Patients with less severe tracheal compression may provide a history of persistent respiratory symptoms without frank stridor, often treated as asthma or bronchiolitis, or they may present with recurrent lower respiratory infections. Esophageal symptoms include emesis, choking, or dysphagia and are more common in older infants and children than in young infants.

Occasionally, patients may reach older childhood or adulthood before developing persistent or progressive symptoms of dysphagia or respiratory symptoms or both.

In newborn infants with associated cardiac or noncardiac anomalies, the ring may be diagnosed incidentally during the course of evaluation for the other anomalies.

Physical: Physical findings can vary, often in accordance with the historic presentation.

Newborns with associated anomalies may have no evidence of a vascular ring on physical examination, but this situation is the exception because most patients have readily recognizable physical signs.

The classic sign of vascular rings in general is nonpositional stridor; however, many young infants with a ring have adventitious expiratory breath sounds as well as the characteristic inspiratory stridor. The respiratory findings generally do not improve with nebulized bronchodilator therapy and usually are more prominent with agitation or crying.

Causes:

Factors responsible for aberrant development of the aortic arch and its branches, as occurs in patients with vascular rings, have not been clearly identified, and the pathogenesis of these anomalies remains unclear. Vascular rings with a right aortic arch typically occur without associated cardiovascular defects, although other lesions may be present, and accordingly are not usually found as part of a syndromic complex.

In a recent study from the author's institution, band 22q11 deletions were found in 8 of 34 patients (24%) with a right aortic arch, vascular ring, and no other cardiac defects. The deletion was found in 8 of 29 patients (28%) with a right arch, aberrant left subclavian artery, and left-sided ductus from the aberrant left subclavian artery to the left pulmonary artery and in none of 5 patients with a right arch, mirror-image branching of the brachiocephalic vessels, and a left ductus from the descending aorta to the left pulmonary artery.

This chromosomal anomaly is associated with aortic arch anomalies in patients with other forms of conotruncal heart disease as well as other isolated vascular abnormalities, and band 22q11 deletion is likely an important etiologic factor in vascular rings with a right aortic arch.

Although band 22q11 deletion was not found in 5 patients with a vascular ring formed by a mirror-image right arch and a left ductus from the descending aorta, this sample is too small to rule out a potential association.

In general, most band 22q11 deletions arise de novo, and no recognizable inheritance pattern is present.

Aortic arch anomalies, including vascular rings, have been induced in a variety of animal models, such as neural crest–ablated chicks, mice with disrupted genes for the endothelin-A receptor or endothelin-converting enzyme, and others. The mechanisms and significance of these models for understanding the development of vascular rings have not been elucidated.

DIFFERENTIALS

Asthma
Bronchiolitis
Congenital Stridor
Croup
Laryngomalacia
Pulmonary Artery Sling
Stridor
Tracheomalacia
Vascular Ring, Double Aortic Arch

Other Problems to be Considered:

Laryngeal stenosis

WORKUP

Lab Studies:

In differentiating vascular rings from upper or lower respiratory infections, a white blood cell count and respiratory viral studies may be helpful. However, because patients with double aortic arch are predisposed to respiratory infections, the diagnosis of an infection does not exclude the possibility of a vascular ring with a right aortic arch.

Because of the possible association between right aortic arch and band 22q11 deletion, a karyotype and a fluorescent in situ hybridization (FISH) test for deletions within band 22q11 may be of value. The diagnosis of band 22q11 deletions allows for targeted evaluation and follow-up for anomalies frequently found in patients with this chromosomal anomaly.

Imaging Studies:

Chest radiography: In patients with a vascular ring formed by a right aortic arch, a chest radiograph may or may not indicate the presence of a vascular ring. In the anteroposterior projection, the presence of a right aortic arch may be realized by the location of the aortic knob and the slight leftward deviation of the lower trachea. On the lateral chest radiograph, posterior indentation of the trachea may be visualized.

Echocardiography: In most cases, the diagnosis of a right aortic arch with aberrant branching can be made reliably with echocardiography with the useful information obtained using suprasternal, high parasternal, and subcostal imaging. However, the presence of a vascular ring cannot always be confirmed and may be missed altogether if the ring is the form with mirror-image branching of the brachiocephalic vessels. Echocardiography is not necessary in the evaluation of patients with a suspected vascular ring if other more valuable imaging studies are available.

Magnetic resonance imaging: MRI is the best single imaging study for the diagnosis and characterization of vascular rings. It provides complete information about the arterial branching pattern, clearly demonstrates the locations and extent of airway and esophageal obstruction, and can be used to delineate cardiac anatomy. In addition to tomographic images, 3-dimensional reconstruction of the aorta and airways can be a useful tool for preoperative planning.

Cardiac catheterization: Cardiac catheterization is not usually indicated in patients with vascular rings.

Angiography: Although angiography was once the criterion standard for the diagnosis of rings, MRI is both less invasive and diagnostically superior. Angiography may be somewhat confusing because of the overlapping projection of the various vascular structures. This problem may be ameliorated somewhat by the use of digital subtraction angiography or countercurrent brachial arteriography, which provides sequential information that can help clarify the aortic branching pattern.

Barium esophagography: Frequently, the diagnosis of a vascular ring is initially made with barium esophagography. In patients with a right aortic arch, a right-sided indentation of the esophagus may be observed on the anteroposterior view, depending on the tightness of the ring. Posterior indentation of the esophagus is nearly always present on the lateral view. Although this test is not necessary to make the diagnosis of a vascular ring, it is often obtained in the preliminary evaluation of patients with symptoms of upper airway and/or esophageal pathology. If a ring is strongly suspected on the basis of findings on chest radiography or echocardiography, barium esophagography is not indicated. Rather, if additional imaging is desired, a more thorough diagnostic study, such as MRI, should be performed.

Other Tests:

ECG: No characteristic electrocardiographic findings are associated with vascular rings, and, except in patients with associated cardiovascular anomalies, electrocardiographic findings usually are normal.

Procedures:

Diagnostic procedures are not generally necessary in the evaluation of patients with a right aortic arch.

Bronchoscopy may be obtained in the evaluation of a patient with suspected airway pathology but is not indicated in most patients. Pulsatile compression of the anterior and lateral walls of the trachea can be observed in patients with a vascular ring and a right aortic arch, but the specific type of vascular ring cannot always be determined. Other imaging modalities, especially MRI, permit characterization of the severity and location of tracheal obstruction while offering superior definition of vascular anatomy.

In some cases, depending on surgeon preference, bronchoscopy may be performed in the operating room before and after repair of the vascular ring to determine the efficacy of relief of tracheal compression. This is of particular value in young patients in whom persistent tracheomalacia is a concern.

Histologic Findings: No need for histologic tissue examination exists in patients with a right aortic arch.

TREATMENT

Medical Care:

Medical care before surgical repair depends on the clinical presentation. In most cases, only supportive management is required.

Catheter interventions are not used in the management of vascular ring formed by a right aortic arch.

Surgical Care:

Indications: Surgical division of the vascular ring is indicated in any patient with symptoms of airway or esophageal compression and in patients undergoing surgery for repair of associated intracardiac or thoracic anomalies.

Techniques: The fundamental principle of surgical management of vascular rings is division of the ring to relieve compression of the trachea and esophagus.

In patients with all forms of vascular ring with a right aortic arch and a left-sided ductus arteriosus or ligamentum arteriosum, this is achieved by dividing the ductus/ligamentum through a left thoracotomy. Dissection should be carried down to the trachea and esophagus to ensure that no constricting fibrous bands remain. In patients with an aberrant subclavian artery in whom concern exists over residual posterior compression of the trachea or esophagus, arteriopexy may be performed by suturing the retroesophageal diverticulum to the prevertebral fascia.

Video-assisted thoracoscopic division of vascular rings is performed at several centers and seems to be an effective approach in most cases, but data on outcomes are limited.

When associated intracardiac anomalies require surgery through a median sternotomy, division of the ductus/ligamentum is performed during the same procedure.

Results: In the current era, essentially no operative mortality is associated with repair of isolated vascular rings. Outcomes in patients with associated anomalies depend on the coexisting condition.

Postoperative care/precautions: Postoperative care after division of a vascular ring is similar to that for patients undergoing other cardiovascular procedures through a thoracotomy. Most patients experience immediate relief after surgery, although persistent respiratory symptoms and signs may be present, especially in very young infants with severe symptoms preoperatively. Except in patients undergoing concurrent repair of associated anomalies, cardiopulmonary bypass is not employed during the repair, so postoperative cardiac function is generally not a problem.

Complications: Complications in the early postoperative period are uncommon after division of a vascular ring.

The major issue is persistent respiratory symptoms, especially in neonates who are more susceptible to tracheomalacia. Occasionally, the tracheomalacia is severe. Over time, though, this tends to improve with relief of the vascular ring.

Other rare operative complications include chylothorax due to injury to the thoracic duct, diaphragmatic paresis/paralysis secondary to phrenic nerve injury, and vocal cord paresis/paralysis resulting from injury to the recurrent laryngeal nerve.

Consultations: Unless specific associated anomalies or problems are identified, consultations are generally not necessary. As noted above, band 22q11 deletion is present in a substantial proportion of patients with vascular rings. A consultation with a geneticist is indicated in patients with other characteristic features of the band 22q11 deletion syndrome and may be appropriate in young infants, in whom typical features of the syndrome may not yet be evident.

Diet: No special dietary considerations are indicated in patients with a vascular ring other than those dictated by associated conditions. Postoperatively, enteral feeding is resumed as soon as possible. In patients with dysphagia or emesis as a presenting symptom, adequate oral intake should be verified and feeding therapy instituted if necessary. In patients with band 22q11 deletion, velopharyngeal insufficiency or cleft palate is frequently present; oral feedings should be resumed with the aid of feeding specialists.

Activity: Patients with vascular rings are not subject to specific restrictions on activity. Prior to repair, their activity may be limited by symptoms. Following repair, any persistent respiratory symptoms due to tracheomalacia should dictate activity limitations.

MEDICATION

Aside from analgesia, pharmacologic therapy is not typically required in patients with a vascular ring with a right aortic arch unless associated conditions are present.

FOLLOW-UP

Further Inpatient Care:

Routine postthoracotomy care is provided following division of a vascular ring. Patients are removed from mechanical ventilation as soon as possible, and tube thoracostomy is generally discontinued on the first postoperative day. The remainder of the inpatient stay is focused on determining and managing any residual symptoms, providing sufficient enteral nutrition, transitioning the patient to enteral analgesics, and educating the parents.

Further Outpatient Care:

Close follow-up should be maintained after division of a vascular ring, especially in young children with persistent tracheomalacia or other respiratory symptoms. Additional imaging or bronchoscopic evaluation is not indicated unless persistent residual symptoms or other mitigating circumstances are present.

In/Out Patient Meds:

Aside from analgesic medications, pharmacologic therapy is generally not required after removal from mechanical ventilation. Relief from the pain of the thoracotomy incision may be achieved with age-appropriate narcotic and nonsteroidal anti-inflammatory medications.

Transfer:

After postoperative stabilization in the intensive care unit and removal from mechanical ventilatory support, the patient may be transferred to the regular inpatient care area for advancement of feedings and additional postoperative care.

Deterrence/Prevention:

No methods are known that prevent the development of vascular ring with a right aortic arch.

Complications:

Complications are uncommon after repair of vascular rings.

The major postoperative issue is persistent respiratory symptoms, including cough, dyspnea, and wheezing. Pulmonary function testing reveals persistent upper airway obstruction in some patients. Others have evidence of lower airway obstruction that is generally responsive to bronchodilator therapy. Whether the incidence of lower airway obstruction is higher in patients who have undergone repair of vascular rings than in the general population or whether such pathology in patients with rings has any relationship to their prior anatomic and functional abnormalities is not known.

Prognosis:

The long-term prognosis for patients with repaired vascular rings is excellent, with persistent respiratory symptoms being the most common adverse outcome.

Patient Education:

For the early posthospital period, parents must be educated about the possible persistence of symptoms, the potential benefit of prone positioning in patients with tracheomalacia, signs and symptoms of aspiration, and management of the thoracotomy incision.

No dietary or activity restrictions are indicated after repair of an isolated vascular ring.

In patients with a repaired vascular ring, lifestyle implications are minimal and are most likely related to residual symptoms or associated anomalies.

No special issues or concerns related to pregnancy in patients with repaired vascular ring exist. In patients with an unrepaired ring, pregnancy-induced physiologic changes should not be of special concern, although symptoms may be exacerbated in certain situations.

MISCELLANEOUS

Medical/Legal Pitfalls:

The most significant potential medicolegal pitfall is failure to diagnose and properly define the anatomy of a vascular ring.

PICTURES

Caption: Picture 1. Vascular ring, right aortic arch. Left: Schematic diagram of the primitive pharyngeal arch system showing the left (L) and right (R) external carotid (EC) and internal carotid (IC) arteries, the fourth (IV) and sixth (VI) pharyngeal arches, distal pulmonary arterial segments (PA), dorsal aortas (DA), and seventh intersegmental arteries (VII). The proximal (p) sixth arches develop into the proximal pulmonary arteries, and the distal (d) sixth arches become the arterial ducts. The seventh intersegmental arteries develop into the subclavian arteries. Right: Schematic diagram depicting the segments of the pharyngeal arch system that regress (shown in black) in order for normal development of the great arteries and their thoracic branches (common carotid artery [CCA], left pulmonary artery [LPA], ductus arteriosus [PDA], right pulmonary artery [RPA], subclavian artery [SCA]).

Picture Type: Image

Caption: Picture 2. Vascular ring, right aortic arch. Left: Schematic diagram depicting the segments of the pharyngeal arch system that regress (shown in black) in order for the development of a right aortic arch with aberrant left subclavian artery. Abbreviations are as in Image 1. Right: Mature anatomy of a vascular ring formed by a right aortic arch with an aberrant left subclavian artery arising from a retroesophageal diverticulum with a left-sided ligamentum arteriosum to the left pulmonary artery.

Picture Type: Image

Caption: Picture 3. Vascular ring, right aortic arch. Left: Schematic diagram depicting the segments of the pharyngeal arch system that regress (shown in black) in order for the development of a right aortic arch with mirror-image branching of the brachiocephalic vessels and a left-sided ductus arteriosus from the descending aorta to the left pulmonary artery. Abbreviations are as in Image 1. Right: Mature anatomy of a vascular ring formed by a right aortic arch with mirror-image branching of the brachiocephalic vessels and a left-sided ductus arteriosus from the descending aorta to the left pulmonary artery.

Picture Type: Image

Caption: Picture 4. Vascular ring, right aortic arch. Left: Schematic diagram depicting the segments of the pharyngeal arch system that regress (shown in black) in order for the development of a right aortic arch with aberrant retroesophageal left innominate artery. Abbreviations are as in Image 1. Right: Mature anatomy of a vascular ring formed by a right aortic arch with an aberrant retroesophageal left innominate artery with a left-sided ligamentum arteriosum to the left pulmonary artery.

Picture Type: Image

Vascular Ring, Right Aortic Arch