This is a 6 week old male with a previous diagnosis of laryngomalacia who presents with increasing stridor, respiratory distress and wheezing. There has been no associated apnea or cyanosis. He had been feeding well with no vomiting or choking. He has had no fever. Initial CXR revealed no acute infiltrates. He received albuterol but had a minimal response.

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 fissures. O2 sat 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 surgeon with a flexible bronchoscopy which revealed mild laryngomalacia. His condition improved and he was discharged home in stable condition.

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 gr 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 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 bowed anteriorly. Coupled with the clinical findings (airway symptoms since birth, current presentation with stridor), these findings raise the suspicion of tracheal compression, such as with a vascular ring. He is treated with bronchodilators, racemic epinephrine and suctioning for his acute symptoms. A CT of the chest reveals findings suspicious for a double aortic arch and an esophagram reveals a posterior indentation on the esophagus. MRI and MRA studies confirm the diagnosis of a double aortic arch (the aorta ascends and splits such that one arch travels anterior to the trachea and over the left mainstem bronchus, while the other arch travels over the right mainstem bronchus and posterior to the esophagus and trachea, at which point, both branches join together to form the descending aorta). Echocardiography also suggests a double aortic arch. He undergoes a surgical correction and postoperatively he improves, but he continues to have mild stridor. Bronchoscopy reveals mild tracheal stenosis.

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. They arise from abnormal embryonic development of the aortic arches. When the abnormal blood vessels encircle the trachea and esophagus, it is termed a vascular ring. These rings may be complete or incomplete. The severity of symptoms depend on the degree of compression on the trachea and esophagus.

Multiple paired branchial arches and paired dorsal aorta sequentially fuse and resorb in embryonic development. This results in a left aortic arch (i.e., the aortic arch travels over the left mainstem 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.

Paired right and left dorsal aorta are present in an embryo at approximately 21 days. They come together at the aortic sac. Six branchial arches form along with its 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 maxillary and hyoid/stapedial arteries respectively. The 3rd arch becomes the common 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.

Edwards was the first to describe embryonic pathophysiologic mechanisms in 1948. 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% of all congenital heart disease. Some vascular rings are associated with other congenital heart lesions while others are isolated defects. Tracheobronchial anomalies are seen with vascular rings but are more highly associated with pulmonary artery 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. 70-90% have a dominant right aortic arch with the left arch hypoplastic or atretic. The aorta ascends from the heart and splits such that one arch travels anterior to the trachea and over the left mainstem bronchus, while the other arch travels over the right mainstem bronchus and posterior to the esophagus and trachea, at which point, both branches join together to form the descending aorta. The double aortic arch forms a ring around the trachea and esophagus (hence the term vascular ring) compressing both the trachea and esophagus. Tracheoesophageal compression will result in early symptoms. This type of vascular ring is rarely associated with intracardiac defects.

The second most common vascular ring is the right aortic arch, aberrant left subclavian with a left ligamentum arteriosum. In this malformation, the aorta ascends from the heart anterior to the tracheal bifurcation, to arch over the right mainstem 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) connects the left subclavian or descending aorta (depending on its origin) 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 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.

A third type of vascular ring is the right aortic arch with mirror branching vessels. It results from persistence of the right dorsal aorta and regression of the left dorsal aorta. A complete ring is completed only if the ductus arises from the upper descending aorta. If the ductus arises from the left subclavian, an incomplete ring is formed. This type of vascular ring has greater than 90% association with intracardiac defects. This can be explained by the hemodynamics in developing hearts. Normally, formation of a vessel occurs as a result of blood flow through it. In a normally structured heart, blood is ejected to the left side stimulating the formation of the left arch. If there is abnormal blood flow due to internal structure such that blood is ejected to the right, persistence of the right arch will develop. Approximately 25% will have tetralogy of Fallot, 20% will have double outlet right ventricle and 25% will have truncus arteriosus.

A fourth type of vascular ring is the left aortic arch and aberrant right subclavian artery. This 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 has a higher association with coarctation of the aorta.

A pulmonary sling is the left pulmonary artery arising from the right pulmonary artery. This is also known as anomalous pulmonary artery. This 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 as it arrives on the left side. Most of these patients are symptomatic by 1 month of age. Respiratory symptoms predominate as the compression is most severe on the trachea. 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 also is associated with intracardiac defects present in 10-20%.

Respiratory symptoms predominate in initial presentation. These symptoms occur from tracheobronchial compression from the vascular ring or pulmonary sling. The severity of compression determines the severity of symptoms. 70-97% of patients will have respiratory symptoms. Stridor is present in 97% of cases. 65% will present on the first day of life. Stridor may be more pronounced during feeding or activity. Wheezing, air trapping and hyperinflation are also common. Many infants may have recurrent pneumonias. Diagnosis is difficult due to the rarity of these anomalies and the common symptoms these infants 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 infants are diagnosed by age 12 months. The most common cause of stridor is laryngomalacia. This also is seen at birth and can easily mask symptoms from a vascular ring.

Symptoms of dysphagia are less common. This occurs from compression of the esophagus posteriorly from the vascular ring. 5-15 % of patients will have dysphagia alone. Symptoms include slow breast or bottle feeding, fatigue with feeding, frequent regurgitation and aspiration pneumonias. Many times the diagnosis is made when solid foods are introduced and dysphagia symptoms are more pronounced.

Again, the more severe the compression, the more severe the symptoms and the earlier age of presentation. Double aortic arch, right aortic arch with left ligamentum arteriosum and anomalous pulmonary artery present early in infancy. Aberrant left subclavian artery may be clinically silent or present in adolescence/adulthood with dysphagia.

Evaluation of suspected vascular rings should 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, the signs of a vascular ring are usually too subtle to be routinely diagnostic. A positive esophagram may provide supporting evidence of a vascular ring, but the other imaging modalities are superior.

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 mainstem bronchus). Hyperinflation of the left lung with the left hilum lower than the right suggests a pulmonary sling.

Echocardiography is useful in evaluating for associated intracardiac defects. It is possible but difficult to completely delineate the anatomy of the vascular ring on the echocardiogram alone.

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 some characteristics 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.

CT scan can be used to identify structures in the thoracic cavity. It is fast and no sedation is usually required. It is however difficult to identify the ligamentum or an atretic branch of the aortic arch. MRI can more definitively identify the vascular ring as well as the tracheoesophageal anatomy. This however requires sedation and more time.

Angiography was used prior to the advancement in CT and MRI. It provides anatomy of the abnormal vessels and also identifies associated congenital heart defects. It fails to show atretic portions of vessels and is unable to identify nonvascular anomalies.

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 will resolve with growth. It is however necessary to surgically correct patients with pulmonary slings, double aortic arch and right arch with a left ligamentum arteriosum. 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. This is expected to resolve with growth. In 95% of patients, surgical correction of the vascular ring is curative. Patients with pulmonary slings have a much higher percentage of tracheobronchial anomalies. Some of these patients will need further surgery to correct their tracheal 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 or bronchoscopy for tracheal anomalies. Early surgical correction is safe and effective. Mild respiratory symptoms persist postoperatively but are expected to resolve.

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. All of the following studies could find evidence to support the diagnosis of a suspected vascular ring except:
. . . . . a. Esophagram
. . . . . b. Pulmonary function tests
. . . . . c. CXR
. . . . . d. Echocardiogram

6. Describe the structures which form the vascular ring in a double aortic arch.

7. 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. Valletta EA, Pregarz M, Bergamo-Andreis IA, Boner AL. Tracheaoesophageal Compression Due to Congenital Vascular Anomalies (Vascular Rings). Pediatr Pulmonology 1997;24(2):93-105.

2. Bakker DAH, Berger RMF, Witsenburg M, Bogers AJJC. Vascular Rings: A Rare Cause of Common Respiratory Symptoms. Acta Paediatr 1999;88(9):947-952.

3. Woods RK, Sharp RJ, Holcomb GW, et al. Vascular Anomalies and Tracheoesophageal Compression: A Single Institution's 25-Year Experience. Ann Thoracic Surg 2001;72(2):434-439.

4. Marmon LM, Bye MR, Haas JM, et al. Vascular Rings and Slings: Long-Term Follow-Up of Pulmonary Function. Journal of Pediatric Surgery 1984;19(6):683-692.

5. Berdon WE. Rings, Slings, and Other Things: Vascular Compression of the Infant Trachea updated from the Midcentury to the Millennium-The Legacy of Robert E. Gross, MD, and Edward B.D. Neuhauser, MD. Radiology 2000;216(3):624-632.

6. Kocis KC, Midgley FM, Ruckman RN. Aortic Arch Complex Anomalies: 20-Year Experience with Symptoms, Diagnosis, Associated Cardiac Defects, and Surgical Repair. Pediatr Cardiology1997;18(2):127-132.

Answers to questions

1.b, 2.c, 3.c, 4.b, 5.b

6.right aortic arch, left aortic arch, connecting to the descending aorta.

7. A vascular ring involves the aorta and its branches. A vascular sling involves the pulmonary artery. In the vascular sling, the left pulmonary artery arises from the right pulmonary artery and compresses the trachea posteriorly.