Chapter VII.7. Vascular Rings and Slings
Colin Petko, MD
May 2013

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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, Dr. Cheryl M. Takao. This current second edition chapter is a revision and update of the original authorís 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. Initial CXR revealed no acute infiltrates. He received albuterol at his pediatrician's office but had a minimal response. Mom notes that his symptoms are worse when he is agitated and improve somewhat when he is calm or asleep.

He was born at term via NSVD with 8 and 9 Apgars. No intubation required. Mild respiratory distress was noted on his first day of life. A CXR revealed fluid within the fissures. Oxygen saturation on 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 bronchoscopy revealed mild laryngomalacia. His condition improved slightly and he was discharged home in stable condition, however the noisy breathing never entirely went away.

Family history: Father, 12 y.o. brother, 7 y.o. and 18 month old sister with 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 BS, diffuse wheezes, subcostal retractions. Abdomen is benign without organomegaly. Femoral pulses are 2+ bilaterally. No skin rashes are noted. His color is pink and his perfusion is good. No neurologic abnormalities are noted.

A chest radiograph (CXR) is obtained which shows clear lung fields. Close examination of the trachea on the lateral view shows that the trachea is narrowed and it appears to be anteriorly bowed. Coupled with the clinical findings (airway symptoms since birth, current presentation with stridor), these findings raise the suspicion of tracheal compression. 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, 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). An esophagram suggested by a more seasoned radiologist reveals a posterior indentation on the esophagus. Echocardiography 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 which consists of division of the smaller left aortic arch through a left lateral thoracotomy. Postoperatively he improves, but he continues to have mild stridor for 2-3 months.


BACKGROUND

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. 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 1st to appear and the 1st to regress. The 1st and 2nd aortic arch 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.

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 embryonic pathophysiologic mechanisms of aortic arch development in 1948. The classic vascular rings will result from disruption at 4 points in the normal development. The 1st point is at the right dorsal aorta. This normally will regress but if it persists, a double aortic arch will develop. The 2nd 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 3rd 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 4th 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. Vascular rings encompass only 1-3% of all congenital heart disease. 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.

TYPES OF RINGS AND SLINGS

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. 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. 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.

Double aortic arch. 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. Available online at: www.hawaii.edu/medicine/pediatrics/pemxray/v6c19.html

The second most common vascular ring is the right aortic arch with aberrant left subclavian and a left ligamentum arteriosum. In this malformation, the aorta ascends from the heart anteriorly to the tracheal bifurcation, to arch over the right main stem bronchus. 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. 10% of this type of ring will have associated intracardiac defects.

Right sided aortic arch with aberrant (anomalous) left subclavian artery. 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. Available online at: www.hawaii.edu/medicine/pediatrics/pemxray/v6c19.html

A third type of vascular ring is the right aortic arch with mirror image (to the normal left aortic arch) branching vessels. 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. This type of vascular ring has greater than 90% association with intracardiac defects. Of these, approximately 25% are Tetralogy of Fallot, 20% Double Outlet Right Ventricle (DORV) and 25% Truncus Arteriosus.

A fourth type of vascular ring is the left aortic arch and aberrant right subclavian artery. This defect is the most common anomaly involving the aortic arch, but is usually asymptomatic. 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. The aberrant right subclavian travels posterior to the esophagus to the right side. 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 coarctation of the aorta.

A pulmonary sling is the left pulmonary artery arising from the right pulmonary artery. It is also known as 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. 50% 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. This anomaly is associated with intracardiac defects in 10-20% (most commonly ASD and VSD).

PRESENTATION

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. 70-90% of patients will have respiratory symptoms. 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 (so called dysphagia lusoria).

Symptoms of dysphagia are less common but 5-15 % of patients will have dysphagia as an isolated symptom initially. Dysphagia occurs because of posterior compression of the esophagus by the vascular ring. Symptoms include slow breast or bottle feeding, fatigue with feeding, frequent regurgitation and aspiration pneumonias. Often, the diagnosis is made only after solid foods are introduced and dysphagia symptoms are more pronounced.

DIAGNOSIS

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, however. The most common cause of stridor, laryngomalacia, can easily mask symptoms from a vascular ring.

Evaluation of suspected vascular rings can include a chest x-ray, esophagram, echocardiogram and a CT or MRI. There is much debate on the radiographic 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. A positive esophagram may provide supporting evidence of a vascular ring, but is not mandatory if the diagnosis is suspected.

There are subtle characteristics of CXR findings for each type of vascular ring. An anterior indentation of the trachea at or above the carina on a lateral film suggests a complete ring or anomalous innominate artery (not discussed in this chapter). A right sided aortic arch may suggest a vascular ring and this can occasionally be suspected if the distal trachea is slightly deviated to the left (due to the aorta arching over the right main stem bronchus). Hyperinflation of the left lung with the left hilum lower than the right suggests a pulmonary sling.

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 correction of tracheal anomalies will be performed at the same time. If bronchoscopy is done prior to 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 posterior.

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 the imaging modality is typically individualized depending on the facility and taking into account patient safety factors (need for and duration of sedation, radiation).

Angiography was used prior to the advances in CT and MRI imaging but has become obsolete.

TREATMENT

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 as these patients will progressively become more symptomatic over time.

Postoperatively, many patients will have respiratory symptoms related to tracheomalacia and airway obstruction. 10% of patients have symptoms that persist for months. 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 outcome.


Questions

1. Which vascular anomaly will exhibit a complete vascular ring?
. . . . . a. right aortic arch, mirror branching, left ligamentum from left subclavian
. . . . . b. right aortic arch, aberrant left subclavian
. . . . . c. left aortic arch, aberrant right subclavian
. . . . . d. pulmonary sling

2. Which vascular anomaly may present in adolescence or adulthood with dysphagia?
. . . . . a. double aortic arch
. . . . . b. right aortic arch, aberrant left subclavian
. . . . . c. left aortic arch, aberrant right subclavian
. . . . . d. pulmonary sling

3. What vascular anomaly is most associated with severe tracheobronchial anomalies?
. . . . . a. Right aortic arch, left subclavian
. . . . . b. Double aortic arch
. . . . . c. Pulmonary artery sling
. . . . . d. All of the above

4. All of the following are common symptoms of vascular rings except:
. . . . . a. wheezing
. . . . . b. hoarse cry
. . . . . c. stridor
. . . . . d. dysphagia

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

X-rays and diagrams of vascular ring case: 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. Available online at: www.hawaii.edu/medicine/pediatrics/pemxray/v6c19.html

X-rays of vascular ring case: 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. Available online at: www.hawaii.edu/medicine/pediatrics/pemxray/v6c20.html

References

1. Yoon, S.-J., Bradley, T.R. Vascular Rings, Pulmonary Artery Sling, and related conditions. Paediatric Cardiology, 3rd edition, Elsevier 2010, 967-989

2. Powell, A.J., Mandell, V.S. Vascular Rings and Slings. Nadas Pediatric Cardiology, 2nd edition, Elsevier 2006, 811-825

3. Weinberg, P.M., Natarajan, S., Rogers, L.S. Aortic Arch and Vascular Anomalies. Moss and Adams Heart Disease in Infants, Children, and Adolescents, 8th edition, Lippinkott Williams and Wilkins, 758-798


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. In the vascular sling, the left pulmonary artery arises from the right pulmonary artery and courses leftward between trachea and esophagus and thus forms a sling that compresses the trachea posteriorly.


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