Figure 1. Double aortic arch. L left; R right; A. artery.
The editors and current author would like to thank and acknowledge the significant contribution of the previous author of this chapter from the 2004 first edition and the 2013 second edition, Dr. Cheryl M. Takao and Dr. Colin Petko. This current third edition chapter is a revision and update of the original author’s work.
This is a 6-week-old male with a previous diagnosis of laryngomalacia who presents to the emergency room with increasing stridor, respiratory distress and wheezing. There has been no associated apnea or cyanosis. The infant has been feeding well with no vomiting or choking. He has had no fever and there have been no sick contacts. An earlier chest radiograph (CXR) revealed no acute infiltrates. He received albuterol at his pediatrician's office with minimal response. Mom notes that his symptoms are worse when he is agitated and he improves somewhat when he is calm or asleep.
He was born at term with 8 and 9 Apgars. No intubation was required. Mild respiratory distress was noted on his first day of life. A CXR revealed fluid within the fissures. Oxygen saturation on room air (RA) was 98%, so transient tachypnea of the newborn was initially suspected. On the second day of life, he was noted to have stridor. He was evaluated by ENT and a flexible laryngoscopy revealed mild laryngomalacia. His condition improved slightly, and he was discharged home in stable condition; however his noisy breathing never entirely resolved
Family history: Several family members have asthma.
Exam: VS T 37.1, HR 160, RR 52, BP 109/56, oxygen saturation in RA 98%. Wt. 5.3kg (75%), Ht 52.5cm (10%), HC 39.5cm (90%). He is lying in mother's arms, visibly tachypneic, with audible congestion. HEENT and neck exams are normal. Heart RRR, with grade II/VI systolic ejection murmur at the left sternal border. Lung exam shows inspiratory and expiratory stridor, coarse breath sounds, diffuse wheezes, subcostal retractions. Abdomen is benign without organomegaly. Femoral pulses are 2+ bilaterally. No skin rashes are noted. His color is pink and perfusion is good. No neurologic abnormalities are noted.
A CXR is obtained which shows clear lung fields. Close examination of the trachea on the lateral view shows that the trachea is narrowed and appears to be anteriorly bowed. Coupled with the clinical findings (airway symptoms since birth, current presentation with stridor), tracheal compression is suspected. He is treated with bronchodilators, racemic epinephrine and suctioning with some but minimal improvement of symptoms. A CT of the chest reveals a double aortic arch (the aorta ascends and splits such that one arch travels anterior to the trachea and over the left main stem bronchus (a left-sided arch), while the other arch travels over the right main stem bronchus (a right-sided arch) and posterior to the esophagus and trachea, at which point, both branches join together to form the descending aorta). This aortic ring is compressing both the esophagus and the trachea (accounting for his respiratory symptoms). The radiologist tells you that before CT scanning, esophagrams were performed which showed a posterior indentation in the esophagus caused by the right-sided aortic arch. An echocardiogram is obtained which also suggests a double aortic arch with patency of both left and right aortic arches but otherwise normal intracardiac anatomy. The patient undergoes surgical correction of this condition. Postoperatively he improves, but he continues to have mild stridor for 2 to 3 months, which eventually resolves completely.
Vascular rings and pulmonary slings are congenital anomalies of the aortic arch and pulmonary artery. They are very important but rare causes for common respiratory symptoms, especially in infants. Their etiology is related to abnormal development of the embryonic aortic arches. When the abnormal blood vessels form a ring around the trachea and esophagus, it is termed vascular ring. These rings may be complete or incomplete. The severity of symptoms depends on the degree of compression of the trachea and esophagus.
Paired right and left dorsal aortae are present in an embryo at approximately 21 days (1). They come together at the aortic sac. Six branchial arches form along with their own aortic arches that communicate with the aortic sac. The appearance and regression of the aortic arches follow the number they are assigned. The 1st aortic arch is the first to appear and the first to regress. The 1st and 2nd aortic arches form the external carotid and hyoid/stapedial arteries respectively. The 3rd arch becomes the common and internal carotid arteries. The 4th arch forms the proximal portion of the subclavian on the right and the aortic arch segment on the left. The 5th arch has no known derivatives. The 6th arch develops into the pulmonary arteries and the ductus arteriosus (2).
Parts of the initially paired branchial arches and dorsal aortae undergo a process of fusion as well as regression. The correct sequence results in a left aortic arch (i.e., the aortic arch travels over the left main stem bronchus) and left descending aorta. Failure of regression or persistence of normally regressed portions will result in one of many vascular rings or a pulmonary artery sling.
Edwards was the first to describe the embryonic pathophysiologic mechanisms of aortic arch development in 1948 (3). The classic vascular rings will result from disruption at 4 points in the normal development. The first point is at the right dorsal aorta. This normally will regress but if it persists, a double aortic arch will develop. The second point is at the right 4th aortic arch. This normally will persist and develop into the proximal portion of the subclavian artery on the right. Failure of this to develop will result in the right subclavian artery to arise from the left aortic arch. The third point is at the left dorsal aorta. This normally persists to form the left descending aorta. If this regresses, a right aortic arch will persist. The fourth point is at the left 4th arch. This normally persists and develops into a portion of the left aortic arch. If this regresses, a right aortic arch will persist and the left subclavian will arise from the right arch (2). Vascular rings encompass only 1% to 3% of all congenital heart disease (4). Some vascular rings are associated with other congenital heart lesions while others are isolated defects. Tracheobronchial anomalies are rarely seen with vascular rings but are common in pulmonary artery slings.
Table 1 summarizes and describes the most common types of vascular rings and pulmonary slings.
Table 1. Common Vascular Rings and Pulmonary Slings
| Double aortic arch | Left and right aortic arches form a ring around the trachea and esophagus | 50% | Respiratory symptoms within 3 months of life | Rare |
| Right aortic arch with aberrant left subclavian artery | Aortic arch to the right of the trachea. Ligamentum arteriosus extends from pulmonary artery to descending aorta. | 30% | 40% of patients experience symptoms from infancy through adulthood | <20% |
| Right aortic arch with mirror image branching | Left subclavian and left carotid arteries arise from innominate artery | 5% | Respiratory symptoms from infancy through childhood | >90%; Tetralogy of Fallot, truncus arteriosus, VSD |
| Left aortic arch and aberrant right subclavian artery | Right subclavian artery arises as last branch on left aortic arch | Very common aortic arch defect, but usually asymptomatic | Asymptomatic in childhood; dysphagia in adolescents or adulthood | Tetralogy of Fallot, coarctation of the aorta, interrupted aortic arch |
| Pulmonary sling | Left pulmonary artery arising from right pulmonary artery | Rare | Respiratory symptoms within first month of life | 50%; Tetralogy of Fallot |
The most common symptomatic vascular ring is the double aortic arch. This results from persistence of the right dorsal aorta. The right and left aortic arches encircle the trachea and esophagus. The right arch is larger than the left in about 75% of cases and typically higher as well (5). The aorta ascends from the heart and splits so that one arch travels anterior to the trachea and over the left main stem bronchus, while the other arch travels over the right main stem bronchus and posterior to the esophagus and trachea, at which point both branches join together to form the descending aorta (Figure 1). The double aortic arch thus forms a ring around the trachea and esophagus compressing both the trachea and esophagus to a variable degree. Tracheoesophageal compression will result in early symptoms with respiratory symptoms commencing typically in the first 3 months of life. This type of vascular ring is rarely associated with intracardiac defects.
Figure 1. Double aortic arch. L left; R right; A. artery.
The second most common vascular ring is the right aortic arch with aberrant left subclavian and a left ligamentum arteriosum (6). In this malformation, the aorta ascends from the heart anteriorly to the tracheal bifurcation, to arch over the right main stem bronchus forming a right-sided aortic arch (Figure 2). It then descends posterior to the esophagus and trachea. The left subclavian comes off the descending aorta. The ligamentum arteriosum (remnant of the ductus arteriosus) in this case typically originates from a bulbous dilation at the base of the left subclavian artery (the so-called diverticulum of Kommerell) and attaches to the left pulmonary artery. The trachea and esophagus are encircled by the ascending aorta anteriorly, the aortic arch on the right, the descending aorta posteriorly and the ligamentum arteriosum and the left pulmonary artery on the left. This malformation results from persistence of the right dorsal aorta, regression of the left dorsal aorta and regression at the left 4th aortic arch. Due to the regression of the 4th arch, the left subclavian develops from the right descending aorta. This type of ring is associated with intracardiac defects in fewer than 20% of cases (7).
Figure 2. Right aortic arch with aberrant left subclavian artery. L left; R right; A. artery.
A third type of vascular ring is the right aortic arch with mirror image (to the normal left aortic arch) branching vessels (Figure 3). It results from persistence of the right dorsal aorta and regression of the left dorsal aorta. A complete ring is formed only if the ductus arises from the upper descending aorta. If the ductus arises from the left subclavian artery, an incomplete ring is formed (1). This type of vascular ring has greater than 90% association with intracardiac defects (7) including tetralogy of Fallot, truncus arteriosus, and ventral septal defect (8,9).
Figure 3. Right aortic arch with mirror image branching. Illustration shows a complete vascular ring with ligamentum arteriosum arising from upper descending aorta. L left; R right; A. artery.
A fourth type of vascular ring is the left aortic arch and aberrant right subclavian artery. This defect is a very common anomaly involving the aortic arch but is usually asymptomatic (1). It results from the regression of the right 4th arch which normally develops into the proximal portion of the right subclavian. The right subclavian now arises as the last branch on the left aortic arch (Figure 4). The aberrant right subclavian branches off the left side of the aortic arch and travels posterior to the esophagus crossing the midline to the right upper extremity. This type of vascular ring is incomplete, and symptoms are minimal. It is occasionally associated with dysphagia occurring in adolescents or adulthood. This lesion has an association with tetralogy of Fallot, coarctation of the aorta, or interrupted aortic arch (4).
Figure 4. Left aortic arch with aberrant right subclavian artery. L left; R right; A. artery.
A pulmonary sling is the left pulmonary artery arising from the right pulmonary artery. It is also known as an anomalous pulmonary artery and results from regression/failure of development of the left pulmonary artery. As the lung buds on each side develop, the right pulmonary artery is stimulated to form collaterals to the left lung. The collaterals eventually enlarge to provide blood flow to the developing left lung, acting as the left pulmonary artery. The pulmonary artery travels between the trachea and esophagus on its course to the left side. About 50% to 79% of these patients also have severe tracheobronchial anomalies such as tracheomalacia, stenosis, webs, complete tracheal cartilage rings called "O" rings (as opposed to the normal "C" cartilage rings) or long segmental stenosis (8,10). This anomaly is associated with intracardiac defects in 50% of these patients (most commonly tetralogy of Fallot) (10,11).
Figure 5. Pulmonary sling. L=left; R=right; A=artery.
In the group of vascular rings and slings as a whole, respiratory symptoms predominate in the initial presentation. The severity of compression determines the severity of symptoms. About 70% to 90% of patients will have respiratory symptoms (1,4). Stridor is present in almost all cases. Stridor may be more pronounced during feeding or activity. Wheezing, air trapping and hyperinflation are also common. Infants may have recurrent pneumonias. Double aortic arch, right aortic arch with left ligamentum arteriosum and anomalous pulmonary artery usually present early in infancy whereas left aortic arch/aberrant right subclavian artery may be clinically silent or present in adolescence/adulthood with dysphagia (known as "dysphagia lusoria").
Dysphagia is the most common GI symptom, but this typically only occurs after solid foods are introduced and dysphagia symptoms are more pronounced (1). Dysphagia occurs because of posterior compression of the esophagus by the vascular ring. Symptoms include slow feeding, frequent regurgitation and aspiration pneumonia.
The diagnosis of vascular rings is challenging. A high index of suspicion is necessary because of the relatively low incidence of these anomalies in contrast to the common symptoms the patients exhibit. Many of the patients will have a delay in diagnosis due to attribution of symptoms to other more common etiologies and the difficulty of establishing this diagnosis without an advanced imaging study such as CT, MRI, echocardiography, or esophagram. Most patients are diagnosed by age 12 months after numerous evaluations for respiratory symptoms (12). The most common cause of stridor, laryngomalacia, can easily mask symptoms from a vascular ring. Symptoms from a vascular ring can often mimic the symptoms of laryngomalacia.
Evaluation of suspected vascular rings can include a chest x-ray, esophagram, echocardiogram and a CT or MRI. There is much debate on the most optimal imaging evaluation for vascular rings due to the advancement in radiographic studies. While CXRs are frequently done early on in the diagnostic process, they are rarely sufficiently diagnostic (4). A positive esophagram might demonstrate an indentation in the esophagus providing supporting evidence of a vascular ring (see Figure 6) but this study can be bypassed to do a more definitive imaging study if a vascular ring is clinically suspected.
Figure 6. Indentation in the esophagus (extrinsic compression) due to a vascular ring. Taken from: Yamamoto LG. Difficulty Breathing Throughout Infancy. In: Yamamoto LG, Inaba AS, DiMauro R (eds). Radiology Cases In Pediatric Emergency Medicine, 1999, volume 6, case 19. Review this case and the image interpretations online at: http://www.hawaii.edu/medicine/pediatrics/pemxray/v6c19.html
There are subtle characteristics of CXR findings for each type of vascular ring. The lateral view is usually more revealing. An anterior indentation of the trachea at or above the carina suggests a complete ring or anomalous innominate artery (not discussed in this chapter). Sometimes, the diameter of the tracheal air column is visibly narrow due to compression by the vascular ring (see Figure 7). The AP or PA view can sometimes yield a very subtle clue by carefully inspecting the bend of the distal tracheal air column which is often deviated ever so slightly to the right, due to the left-sided aortic arch. A right sided aortic arch can be suspected if the distal tracheal air column is slightly deviated to the left (see Figure 8). Hyperinflation of the left lung with the left hilum lower than the right suggests a pulmonary sling.
Figure 7. The lateral view of the chest X-ray demonstrates tracheal narrowing due to extrinsic compression from a vascular ring. Taken from: Yamamoto LG. Difficulty Breathing Throughout Infancy. In: Yamamoto LG, Inaba AS, DiMauro R (eds). Radiology Cases In Pediatric Emergency Medicine, 1999, volume 6, case 19. Review this case and the image interpretations online at: http://www.hawaii.edu/medicine/pediatrics/pemxray/v6c19.html
Figure 8. The normal left sided aortic arch (left image) often results in a subtle bend of the distal tracheal air column to the right. A right sided aortic arch (right image) can sometimes result in a subtle bend of the distal tracheal air column to the left. Taken from: Yamamoto LG. Difficulty Breathing Throughout Infancy. In: Yamamoto LG, Inaba AS, DiMauro R (eds). Radiology Cases In Pediatric Emergency Medicine, 1999, volume 6, case 19. Review this case and the image interpretations online at: http://www.hawaii.edu/medicine/pediatrics/pemxray/v6c19.html
Echocardiography is always indicated to exclude associated intracardiac defects. It is possible but often difficult to completely delineate the anatomy of the vascular ring by echocardiography alone (e.g., the ligamentum arteriosum cannot be seen).
Bronchoscopy is useful when there is suspicion of tracheobronchial anomalies. Identification of these associated anomalies may assist the surgeon if surgical correction of tracheal anomalies will need to be performed at the same time. If bronchoscopy is done prior to the diagnosis, there are characteristic findings of vascular rings. A pulsatile indentation may be seen on the anterior wall of the trachea. In a pulmonary sling, the pulsatile indentation may be on the right side or posteriorly.
Both CT and MRI can accurately define the anatomy and three-dimensional relationships of vascular rings and are mandatory for surgical planning. The choice of imaging modality is typically individualized depending on the facility and considering patient safety factors (i.e., risk factors regarding sedation and radiation exposure). Advanced CT and MRI have largely replaced conventional angiography.
In infants with isolated aortic arch anomalies and no intracardiac defects, consider genetic testing for 22q11.2 deletion syndrome (DiGeorge syndrome). These deletions are found in about 24% of cases (13). However, most patients with classic DiGeorge syndrome will be diagnosed earlier due to thymic aplasia noted on previous CXRs and hypocalcemia (or "seizures" due to tetany).
Vascular rings are surgically corrected if the patient is symptomatic. If the patient is asymptomatic or has mild symptoms, he/she can be monitored and treated conservatively. Many mild symptoms can resolve with growth. It is however always indicated to surgically correct patients with pulmonary slings, double aortic arch and right arch with a left ligamentum arteriosum upon diagnosis since these patients will progressively become more symptomatic over time.
Postoperatively, many patients will have respiratory symptoms related to tracheomalacia and airway obstruction. Reoperation is required in 5% to 10% of patients due to recurrent or persistent symptoms (14). In 95% of patients, surgical correction of the vascular ring is curative. Patients with pulmonary slings have a much higher prevalence of tracheobronchial anomalies. Some of these patients will need further surgery to correct their airway anomalies.
In summary, the diagnosis of a vascular ring or pulmonary sling requires a high index of suspicion. CXR and esophagram may be used for the initial work up, but further anatomic details are obtained by echocardiography, CT/MRI, and bronchoscopy for tracheal anomalies. Early surgical correction is safe with excellent outcomes.
Questions:
1. Which vascular anomaly will exhibit a complete vascular ring?
2. Which vascular anomaly may present in adolescence or adulthood with dysphagia?
3. What vascular anomaly is most associated with severe tracheobronchial anomalies?
4. All of the following are common symptoms of vascular rings except:
5. Describe the structures which form the vascular ring in a double aortic arch.
6. Describe the differences between a vascular ring and a vascular sling.
Related X-rays of vascular ring cases:
In the above CXR, the patient has an esophageal coin, but it is a distraction because this CXR also demonstrates a narrowed tracheal air column (arrow). While this could be due to the coin, the patient also has a vascular ring.
The above esophagram demonstrates and external compression of the esophagus indirectly identifying the vascular ring that is compressing both the trachea and the esophagus. Guzman DD, Goto CS. Recurrent Coins and Recurrent Respiratory Infections. In: Yamamoto LG, Inaba AS, DiMauro R (eds). Radiology Cases In Pediatric Emergency Medicine, 1999, volume 6, case 20. Review this case and the image interpretations online at: http://www.hawaii.edu/medicine/pediatrics/pemxray/v6c20.html
References
1. Worhunsky DJ, Levy BE, Stephens EH, Backer CL. Vascular rings. Semin Pediatr Surg. 2021;30(6):151128. doi: 10.1016/j.sempedsurg.2021.151128.
2. Sadler TW. Chapter 13. Cardiovascular System. In: Langman’s Medical Embryology, 14th edition. 2019. Wolters Kluwer, Philadelphia. pp:179-222.
3. Edwards JE. Anomalies of the Derivatives of the Aortic Arch System. Med Clin North Am. 1948;32(4):925–949. doi: 10.1016/s0025-7125(16)35662-0.
4. Licari A, Manca E, Rispoli GA, et al. Congenital vascular rings: A clinical challenge for the pediatrician. Pediatr Pulmonol. 2015;50(5):511–524. doi: 10.1002/ppul.23152.
5. Backer CL, Mavroudis C, Rigsby CK, Holinger LD. Trends in vascular ring surgery. J Thorac Cardiovasc Surg. 2005;129(6):1339–1347. doi: 10.1016/j.jtcvs.2004.10.044.
6. David S, Ezon DJP. Chapter 33. Aortic Arch and Vascular Abnormalities. In: Allen HD (eds). Moss and Adams’ heart disease in infants, children, and adolescents: including the fetus and young adult, 9th edition. 2016. Wolters Kluwer, Philadelphia. pp:1974–1979.
7. Miranda JO, Callaghan N, Miller O, et al. Right aortic arch diagnosed antenatally: associations and outcome in 98 fetuses. Heart. 2014;100(1):54-59. doi: 10.1136/heartjnl-2013-304860.
8. Ebner L, Huber A, Christe A. Right aortic arch and Kommerell’s diverticulum associated with acute aortic dissection and pericardial tamponade. Acta Radiol Short Rep. 2013;2(1):2047981613476283. doi: 10.1177/2047981613476283.
9. Smith BM, Lu JC, Dorfman AL, et al. Rings and slings revisited. Magn Reson Imaging Clin N Am. 2015;23(1):127–135. doi: 10.1016/j.mric.2014.09.011.
10. Atkins MD, Fuller S. Thoracic Surgery Considerations in the Child and Young Adult. Thorac Surg Clin. 2018;28(1):43–52. doi: 10.1016/j.thorsurg.2017.08.005.
11. Kussman BD, Geva T, McGowan Jr FX. Cardiovascular causes of airway compression. Pediatr Anaesth. 2004;14(1):60–74. doi: 10.1046/j.1460-9592.2003.01192.x.
12. Yong MS, Zhu MZL, Bell D, et al. Long-term outcomes of surgery for pulmonary artery sling in children. Eur J Cardiothorac Surg. 2019;56(2):369–376. doi: 10.1093/ejcts/ezz012.
13. McElhinney DB, Clark BJ, Weinberg PM, et al. Association of chromosome 22q11 deletion with isolated anomalies of aortic arch laterality and branching. J Am Coll Cardiol. 2001;37(8):2114–2119. doi: 10.1016/s0735-1097(01)01286-4.
14. Labuz DF, Kamran A, Jennings RW, Baird CW. Reoperation to correct unsuccessful vascular ring and vascular decompression surgery. J Thorac Cardiovasc Surg. 2022;164(1):199–207. doi: 10.1016/j.jtcvs.2021.08.089.
Answers to questions
1.b, 2.c, 3.c, 4.b
5. Ascending aorta, right aortic arch, left aortic arch, connecting to the descending aorta.
6. A vascular ring involves the aorta, its branches and sometimes remnants of vascular structures forming a ring around trachea and esophagus. A vascular sling involves the pulmonary artery. For a vascular sling, the left pulmonary artery arises from the right pulmonary artery and courses leftward between the trachea and esophagus, thus forming a sling that compresses the trachea posteriorly.