Jul 14, 1982 - ious forms of vascular ring. Additional cardiac malformations were present in five patients, and six had noncardiac congenital anomalies.
Surgical Management of Vascular Ring M. ROESLER, M.D.,* M. DE LEVAL, M.D., A. CHRISPIN, F.R.C.P.,t J. STARK, M.D.
Between 1968 and 1980, 51 children had an operation for various forms of vascular ring. Additional cardiac malformations were present in five patients, and six had noncardiac congenital anomalies. Although symptoms started within the first month of life in 39 infants, only 16 came to operation under three months of age, and a delay of more than six months occurred in 15. Stridor, often life-threatening, and recurrent infections were the most common symptoms, but dysphagia was also important. The reasons for delay in diagnosis are discussed. Barium swallow provided the diagnosis in 44 patients and suggested it in a further four patients. Innominate artery compression of the trachea was not diagnosed by barium swallow. Operations of various types were performed. Accuracy in Jiagnosis is important because not all patients could be treated through the classic left thoracotomy. Severe tracheomalacia was responsible for the only two deaths in the series; one of these had tracheostomy performed in the referring hospital, the second child also had Fallot's tetralogy. The large majority of the patients have done well, 76% being asymptomatic at follow-up. Minimal to moderate stridor persists among the remainder to the present time.
S EVERAL TYPES of congenital vascular anomalies produce partial or total encirclement of the trachea and esophagus. These vascular rings, slings, and other abnormalities associated with the aortic arch may remain asymptomatic despite the abnormality.' Very often, however, the trachea and esophagus are compressed by the abnormality, and then surgical treatment is required. The experience with these conditions at the Hospital
for Sick Children is reported. Although strictly speaking, the term vascular ring should be reserved for the complete encirclement of the trachea and esophagus, for simplicity's sake, these allied anomalies of the aortic arch shall be referred to as a vascular ring. Descriptions of the embryology and the anatomy of the various types of anomalies may be found in a standard textbook.2'3 There are problems in diagnosis and surgical management that need further discussion. Guy's Hospital, St Thomas Street, London SE I 9RT. t Radiology Department, Nottingham City Hospital, Hucknall
*
Road, Nottingham. Reprint requests: J. Stark, M.D., F.R.C.S., Thoracic Unit, The Hospital for Sick Children, Great Ormond Street, London WC1N 3JH, England. Submitted for publication: July 14, 1982.
From the Thoracic Unit, The Hospital for Sick Children, London, Great Britain
Patients From 1952 to 1980, 80 patients have been operated on for various types of vascular ring at the Hospital for Sick Children, Great Ormond Street. The first 29 patients were reported previously.4 The present series consists of 51 cases operated on during a 13-year period from 1968 to 1980. Table 1 shows the various types of vascular anomalies encountered.
Clinical Features The presenting symptoms are reported in Table 2. The age of the patient at the onset of the symptoms is shown in Table 3, the interval between the onset of the symptoms and the operation in Table 4, and the age at the time of operation in Table 5. Eleven (21.5%) of the patients had associated congenital abnormalities, and these are listed in Table 6.
Investigations Chest radiography and a barium swallow were performed in all patients. This established the diagnosis of a vascular ring in 44 of 51 patients. In the 51 patients the esophagram was suggestive but not diagnostically conclusive in only four cases. It was negative in three patients, all having an aberrant origin and course of the innominate artery. It was diagnostic in all the 27 patients with double aortic arch and in five out of six patients with anomalous subclavian artery, in seven out of eight patients with right aortic arch and left ligamentum arteriosum, and in five out of six patients with a pulmonary artery sling. Typical findings in double aortic arch, left arch with right ductus or ligamentum arteriosum, anomalous subclavian artery and pulmonary artery sling are illustrated in Figures 1 a and b, 2, 3, and 4. Patients suspected of having such anomalies have chest radiography; the lateral projection shows the trachea and where it is nar-
0003-4932/83/0200/0139 $01.20 C) J. B. Lippincott Company
139
140
Ann.
ROESLER AND OTHERS TABLE 1. Vascular Ring, 1968-1980, Anatomy
Double aortic arch Right aortic arch and left ligamentum arteriosum 8 Anomalous subclavian artery Pulmonary artery sling Anomalous innominate artery Left aortic arch, right descending aorta and right patent ductus arteriosus
27*
Total
51
6t 6 3 1
* One patient died during operation. t One patient died after operation.
rowed as it traverses the thorax to the carina. A high kilovoltage filtered beam radiograph5 demonstrates the trachea on anteroposterior (AP) projection and should help to define whether the dominant or only aortic arch component lies to the right or left side of the trachea. The barium swallow shows impressions on the esophagus and changes in relationship with the trachea: both AP and lateral projections of the esophagus are essential to a correct analysis. It is based on this investigation that certain decisions as to the need for angiographic study are made and, ultimately, whether left thoracotomy is to be employed or, rarely, an elective right thoracotomy is required. Figure 1 a shows an outline of the findings at barium swallow in vascular ring with a double aortic arch. The dominant right arch component is higher in the chest and produces an impression on the right lateral aspect of the esophagus (Fig. lb). The left arch component is smaller and lower and tends to give an impression on the left lateral aspect of the esophagus at a lower level. In essence, the vascular ring comprising a right arch and left ductus or ligament gives rather similar features. Figure 2 shows the intrathoracic alignment of the esophagus when there is a left arch and a right ductus or ligament running to the right pulmonary artery. There is an absence of an impression on the right lateral aspect of the esophagus, but an impression, lower down on the left lateral aspect. In both the entities described in relationship to Figures 1 and 2, there is on the lateral TABLE 2. Vascular Ring, 1968-1980, Presenting Symptoms
Symptoms
No. of Cases
Recurrent respiratory tract infection Cyanosis Dysphagia Cough Apnoeic attacks Respiratory arrest Respiratory distress Aspiration pneumonia
40 26 16 15 8 5 4 3 2 1
Stridor
Cardiac arrest
Surg. FebrUarY 1983 -
projection a deep impression on the posterior aspect of the esophagus at the level of the right bronchus; tracheal narrowing at this level may also be clearly seen. Figure 3 shows the oblique dark zone within the esophagus produced by an aberrant right subclavian artery.
Figure 4 shows the features on the lateral projection of the aberrant left pulmonary artery. The normal close relationship of the esophagus to the trachea is lost at the point where the left pulmonary artery passes between them. On the anterior aspect of the esophagus, the left pulmonary artery produces its impression, and the trachea may be seen to be narrowed from behind. If the diagnosis is a cause for doubt or anxiety, then angiography may be used to demonstrate that the aberrant left pulmonary artery is responsible for the features and that a small foregut duplication cyst interposed between the esophagus and the trachea, for example, is not causing the problem. Angiographic projections with a radioopaque catheter in the esophagus are required and represent a safe way to conduct the procedure. Patients who have, additionally, cardiac complications will have angiocardiography for these reasons. Angiography was performed in 12 patients: three had an associated heart malformation; three had a diagnostic barium swallow, but angiography had been performed in the referring hospital as part of the routine work up; three had a pulmonary artery sling; two had an anomalous innominate artery; one patient had a left aortic arch, a right descending aorta, and right patent ductus arteriosus. Bronchoscopy was carried out in 12 patients, four had a laryngoscopy, and one had an esophagoscopy. Bronchoscopy was suggestive of a vascular ring in the two cases with aberrant origin of the innominate artery.
Operative Procedures and Findings Forty-eight patients had the classic left thoracotomy. Only two patients were operated through a right thoracotomy; one had a division of a right patent ductus arteriosus associated with a left aortic arch and a right descending aorta, and the other had a division of an aberrant right subclavian artery and ligamentum arterioTABLE 3. Vascular Ring, 1968-1980, Age at the Onset of Symptoms
*
Age
No. of Patients
First day of life 2nd day-I month 2 months-6 months 7 months-I year Total
25* 14 10 2
Two patients died.
51
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SURGICAL MANAGEMENT OF VASCULAR RING TABLE 5. Vascular Ring, 1968-1980, Age at Operation
sum. This last child also had pulmonary atresia and a left aortic arch and had had a previous left thoracotomy for modified (Gore-Tex) Blalock-Taussig shunt. A median sternotomy was performed in a patient who had an aberrant course and origin of the innominate artery: the ascending aorta was elevated and sutured to the sternum. Procedures in Double Arch In the 27 cases of double aortic arch, the dominant arch was posterior in 15 cases and anterior in ten, but in two patients the anterior and posterior components were equal in size. In only one case was the descending aorta on the right side of the spine. The posterior arch was divided in ten cases. The anterior arch was divided distal to the left subclavian artery in 13 cases and between the left carotid and left subclavian in four. The ligamentum arteriosum was divided and the trachea and the esophagus dissected free in all cases. Prior to the division of the arch, a trial test occlusion was routinely performed while the anesthetist was feeling for the carotid pulses.
Procedures in Right Aortic Arch
Of the eight cases with right aortic arch and left ligamentum arteriosum, the upper descending aorta was on the right side in one case. An abnormal course of the innominate and left subclavian arteries with a right aortic arch was the cause of the constriction of the trachea and esophagus in one case: both vessels were attached to the chest wall after ligation of the left ligamentum arteriosum. In another patient, who also had dextrocardia and Fallot's tetralogy, a left aberrant subclavian artery was responsible for stridor: at operation it was found that the trachea was pushed forward by the aortic arch and that it was partly obstructed by the subclavian artery. The left subclavian artery was unsuitable for a shunt, and so it was divided, and a Waterston shunt was performed between the aortic arch and left pulmonary artery. TABLE 4. Vascular Ring, 1968-1980, Interval Between Onset of Symptoms and Operation
Interval
No. of Patients
1 year
16*
Total
51
* One patient died during operation. t One patient died after operation.
20t 8 7
141 No. of Patients
2 years
2 1* 14t I1 10 3
Total
51
* One patient died during operation. t One patient died after operation.
Procedures in Other Lesions In two patients an aberrant right subclavian artery was responsible for their dysphagia; additionally, they had a coarctation of the aorta with mitral regurgitation and pulmonary atresia with ventricular septal defect, respectively. In the first, the coarctation was resected and end-to-end anastomosis was performed. The second child had a previous left thoracotomy for a modified (Gore Tex) Blalock-Taussig shunt. In the remaining two patients, a right aberrant subclavian artery and ligamentum arteriosum were responsible for stridor and dysphagia. In all six cases of pulmonary artery sling, the left pulmonary artery arose from the right pulmonary artery, passing between the trachea and the esophagus with compression of the trachea from behind. In all cases the ligamentum arteriosum was divided, and the left pulmonary artery was dissected free. It was then divided and anastomosed to the main pulmonary artery anterior to the trachea.6 Three patients were operated upon because of stridor due to an abnormal origin and course of the innominate TABLE 6. Vascular Ring, 1968-1980, Associated Anomalies
Cardiovascular Coarctation of the aorta and congenital mitral regurgitation Fallot's tetralogy, dextrocardia Pulmonary atresia with ventricular septal defect and partial Di George disease Ventricular septal defect Gastrointestinal Hiatus hernia, laryngeal cleft, ectopic anus, extrophy of the bladder, epispadia Hare lip, hiatus hernia Large hiatus hernia Hiatus hernia, bilateral choanal atresia, microphthalmos, air trapping in the right lung Other Cleft palate, hare lip, hyperteliorism, coloboma Mental retardation, thick protuberant lips, slanted eyes *
Died after operation.
1*
2
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Ann.
Surg. * February
1983
artery; in one with a left aortic arch the innominate artery bifurcated low into the right carotid and right
subclavian arteries. In all three patients, the ascending by suturing it to the posterior wall
aorta was elevated of the sternum.
In one case, there was a left aortic arch with a right descending aorta and a right aberrant subclavian artery arising as the last vessel from the aortic arch. There was a patent ductus arteriosus opposite to the subclavian artery take-off completing the vascular ring. The diagnosis was confirmed before operation by an angiogram, and the approach was through a right posterolateral thoracotomy. The patent ductus was divided and the trachea and esophagus mobilized. Early Results In the 51 patients operated upon, there were two early deaths. One infant died during operation; this 45-dayold baby with a double aortic arch had been intubated for a considerable period of time and a tracheostomy
FIG. la and b. Barium swallow in a patient with double aortic arch. The impression on the right lateral aspect of the esophagus is produced by the dominant right aortic arch. The impression on the left lateral aspect of the esophagus is caused by the smaller left arch component of the vascular ring.
FIG. 2. Barium swallow in a patient with left aortic arch and right ductus arteriosus. There is an impression on the lower left lateral aspect of the esophagus. Note the absence of the impression on the right lateral aspect of the esophagus.
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SURGICAL MANAGEMENT OF VASCULAR RING
143
had been performed at the referring hospital. When the lung was retracted, the softened trachea distal to the tracheostomy tube prevented ventilation. (In another patient, who narrowly avoided death, ventilation during operation was extraordinarily difficult, and, again, retraction of the lung appeared to be responsible for part of the difficulty. This time the problem could be overcome.) The second death occurred in a five-month-old infant who had an aberrant left subclavian artery causing stridor, respiratory tract infections, and vomiting. In addition, this patient had dextrocardia, tetralogy of Fallot and anomalies of the systemic venous return. The left subclavian artery was ligated, and a central shunt was performed between the aorta and the left pulmonary artery. Severe tracheomalacia at the time of operation was noted. In the postoperative period, this boy required reintubation and ventilation. Despite ventilation, inflation pressure increased sharply, pCO2 rose inexorably and the patient suffered a cardiac arrest from which he could not be resuscitated. As with the other patients in difficulty, tracheal damage appeared to be significant. Postoperative Complications There were many among the 49 patients who came through the operation and subsequently encountered
FIG. 4. Barium swallow in lateral projection. Deep indentation in the anterior wall of the esophagus is caused by aberrant right pulmonary artery passing between the trachea and the esophagus (pulmonary sling).
FIG. 3. This figure shows the oblique dark zone within the barium in the esophagus. This zone is produced by an aberrant right subclavian artery.
postoperative problems. The preoperative tracheal compression frequently appears to have damaged the tracheal wall so that despite the relief of the compression, problems with ventilation may be significant. Postoperative ventilatory management is summarized on Table 7. Forty patients were extubated in the operating theater at the end of the procedure and did well. Two patients were left intubated and ventilated for between two to four days. Four patients in whom extubation had been carried out in the operating theater had to be reintubated shortly afterwards. The reasons were left lung collapse in one patient; cardiac arrest with successful resuscitation in the second patient; a patient (who is mentioned above and who died) had respiratory failure leading to cardiac arrest; the fourth infant was very weak and was thought to have a possible neuromuscular disorder, although this was finally shown not to be present. This last child required ventilation for 14 days and afterwards he did well
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Ann. Surg. * February 1983
ROESLER AND OTHERS TABLE 7. Vascular Ring, 1968-1980, Postoperative Respiratory Management
Follow-up
No. of Patients Extubated at the end of the operation Ventilated after operation Extubated on the table and reintubated on the ward and ventilated Tracheostomy performed
40 3
Total
50
(80%) >
4 3
(14%) (6%)
until severe stridor precipitated his emergency readmission to hospital and a tracheostomy was carried out. Three patients had had tracheostomies performed before the diagnosis of vascular ring had been established. One died and two remained intubated for a considerable period of time after operation. A feature of the preoperative condition of two other infants was that they required intubation and ventilation after birth because of severe respiratory distress and cyanosis. One problem of tracheostomy associated with severe tracheomalacia in one infant was tracheal granuloma, requiring endoscopic resections and followed by tracheal stenosis. In this one instance, it was two years before the tracheostomy tube could be removed. In one instance, the tracheostomy was performed after operation and the patient was then ventilated for two months; the tube was finally removed some three months after operation. Four patients had chylothorax and in two of these it subsided spontaneously with drainage and medium chain triglyceride diet; In the other two patients, the chylothorax necessitated ligation of the thoracic duct. Pulmonary collapse occurred in six patients, affecting one lobe in five and the whole of the left lung in one patient. Congestive cardiac failure secondary to ventricular septal defect developed in one child whose cardiac problem was handled successfully by medication. Pseudomonas aeruginosa septicemia was successfully treated with intravenous antibiotics in another patient. TABLE 8.
Vascuilar Ring, 1968-1980, Long-term Resuilts No. of Patients
%
Asymptomatic Minimal stridor Moderate stridor Recurrent chest infections Tracheal stenosis + recurrent pneumonia Dysphagia
35 3 3 3 1 1
76 6 6 6 2 2
Total
46
Of the 49 survivors, three were lost to follow-up. Table 8 summarizes the follow-up results. Thirty-five patients remained completely asymptomatic. Seventeen lost their symptoms within a month after operation, 13 within six months, three within a year and two within two years. Three patients still have minimal stridor between three and four years after operation; the vascular anomaly was either a distal origin and low bifurcation of the innominate artery or a pulmonary artery sling. Of the three patients who have continued to have moderate stridor, three are still symptomatic at between six months and three years following operation for division of a double aortic arch. Another three patients operated for a double aortic arch still have recurrent respiratory tract infections. One of them had four episodes of severe laryngitis requiring hospital admission. Another patient (who is mentally retarded) still has dysphagia three years after the operation for a vascular ring, caused by a right aortic arch and left ligamentum arteriosum. His recent esophagoscopy and barium swallow showed an extrinsic compression of the esophagus on the right side at the level of the aortic arch and this suggests the obstruction has been incompletely relieved. One patient, operated five years ago for division of anterior aortic arch component has had recurrent pneumonia and pneumothorax. A bronchoscopy, performed at the hospital from which he came, showed considerable tracheal stenosis.
Discussion Symptomatic anomalies of the aortic arch complex tend to present early in life,7'8 although the diagnosis is not always promptly made. In this series 35 (69%) out of 51 patients were operated on quite late, having been symptomatic for at least four months. Some babies with a vascular ring can be critically ill, suffering apneic attacks, respiratory distress, and cardiorespiratory arrest (Table 2). Some of these infants had a tracheostomy before they were referred to this hospital. Stridor, recurrent respiratory tract infections, cyanosis and dysphagia are the most common symptoms. It is conceivable that the severity of the symptoms and the age of onset tend to be proportional to the degree of compression and type of vascular ring. Earlier diagnosis and surgical treatment may provide better results. Stridor in early life may be due to other causes such as laryngomalacia, choanal atresia, and tetany, but most common is infection, and all these conditions need to be excluded. Chest radiographs in the anteropostefior
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SURGICAL MANAGEMENT OF VASCULAR RING
and lateral projections and the barium esophogram are simple, the least traumatic, and most useful investigations indirectly establishing the diagnosis of vascular ring.9"0 A plain film may show signs of general overdistension of the lung, and more recently, high kilovoltage radiography has been employed to demonstrate the position of the aortic arch and the descending aorta in the anteroposterior projection. On these radiographs compression of the trachea may be suspected because of the absence of definable gas in the lumen at the level of the aortic arch. The lateral projection will commonly show the trachea to be narrowed in its anteroposterior diameter at the level of the compression. The diagnosis of double aortic arch, right aortic arch and left ligamentum, and aberrant subclavian artery (causing dysphagia) can be established on the basis of the esophageal study alone. No false positive findings have occurred in this series and it is reasonable to proceed to operation on the basis of these investigations.4'6'7"' For these conditions the left posterolateral thoracotomy provides the best approach and enables the size of the arches and other anatomical malformations to be defined during operation. The arch aortogram is not necessarily helpful in cases of double aortic arch, for one of the arches may not be patent and therefore not visualized, or the vessel and the aortic arch may be superimposed.'2 Aortography is useful when the esophagogram is negative, or when the findings are suggestive but not conclusive. In one case with left aortic arch, right descending aorta, and a patent ductus arteriosus, the patient had stridor. The radiologist suspected the diagnosis on the basis of the esophageal study showing a large indentation on the left posterior aspect of the esophagus.'3 The filtered beam radiograph showed the aorta descended along the right side. Aortography confirmed the anatomy and elective right thoracotomy was carried out." 4 It would have been impossible to perform the operation through the left side of the chest. Only occasionally does an anomalous origin and course of the innominate artery produce symptoms. At bronchoscopy, pulsatile compression of the anterior wall of the trachea suggests the diagnosis.'5"16 It is better to obtain an aortogram with lateral projections, extended upwards to the lower part of the neck. Lateral radiographs preceding aortography may have already indicated the level of the tracheal obstruction in this disorder. In cases in which an anomalous left pulmonary artery is suspected, the esophagogram is usually diagnostic. Uncertainty about the diagnosis or exclusion of other associated cardiac anomalies'7"8 is an indication for ang-
iography.
145
Endoscopic examination did not appear essential in establishing the diagnosis of vascular ring in these patients. It was often done before an esophagogram in cases where the possibility of vascular ring had not been suspected in the first place. However, endoscopy does have a role in the evaluation of tracheal compression due to an aberrant origin of the innominate artery. In these patients the esophageal study is normal. Vascular rings may be associated with other abnormalities'0 and these require additional investigation and treatment. Of the patients in this series, 21.5% had such congenital lesions. Five (10%) had cardiac malformations. The defects are listed on Table 6. Sade et al. reported a high incidence (54% of 67 cases reviewed) of associated anomalies of the tracheobronchial tree. The most common lesion was hypoplasia of the right main stem bronchus usually associated with complete cartilagenous rings.'9 In most patients with vascular ring, or sling, the left posterolateral thoracotomy provides the best surgical approach. In only one of these patients was the approach through a median sternotomy. Two patients had a right thoracotomy as an elective procedure based on preoperative findings. The long-term results of patients operated for vascular ring are gratifying7'8 (Table 8). However, not all patients recover rapidly, and it may take a long time before the structural changes inflicted on the trachea and bronchus by mechanical compression regress. It is hoped that many of these symptomatic patients who are still young will eventually improve. These data do not show a correlation between the length of symptoms before operation and the long-term results. However, the very sick infants whose diagnosis and treatment are delayed do have a high risk of complications, and, therefore, earlier intervention is beneficial. A heightened sense of awareness of the possibility of a vascular ring possibly being present is important. References 1. Godfredson J, Wennevold A, Epsen F, Lauridsen P. Natural history of vascular ring with clinical manifestations. A follow-up of 11 unoperated cases. J Thorac Cardiovasc Surg 1977; 1 1:7577. 2. Stewart JR, Kincaid OW, Edwards JE. An Atlas of Vascular Rings and Related Malformations of the Aortic Arch System. Spring-
field: Charles C Thomas, 1964. 3. Moes CAF. Vascular rings and anomalies of the aortic arch. In: Keith JD, Rowe RD, Vlad P, eds. Heart Disease in Infancy and Childhood. New York: MacMillan Publishing, 1978. 4. Lincoln JCR, Deverall PB, Stark J, et al. Vascular anomalies compressing the oesophagus and trachea. Thorax 1969; 24:295306.
Ann. Surg. * February 1983 ROESLER AND OTHERS 146 12. Tucker BL, Meyer BW, Lindesmith G, et al. Congenital aortic 5. Deanfield JE, Chrispin AR. The investigation of chest disease in vascular ring. Arch Surg 1969; 99:521-523. children by high kilovoltage filtered beam radiography. Br J 13. Wilson DO, Takao A, Sakakibara S. Left aortic arch with right Radiol 1981; 54:856-856. descending aorta. Bull Heart Inst Japan 1967; 99:112. 6. Dunn JM, Gordon I, Chrispin AR, et al. Early and late results 14. Park SG, Siewers RD, Neches WH, et al. Left aortic arch with of surgical correction of pulmonary artery sling. Ann Thorac right descending aorta and right ligamentum arteriosum. J Surg 1978; 28:230-238. Thorac Cardiovasc Surg 1976; 71:779-784. 7. Arciniegas E, Hakami M, Hertzler JH, et al. Surgical management 15. Fearon B, Shortreed R. Tracheobronchial compression by conof congenital vascular ring. J Thorac Cardiovasc Surg 1979; genital cardiovascular anomalies in children. Syndrome of ap77:721-727. nea. Ann Otol Rhinol Laryngol 1963; 72:949-955. 8. Nikaidoh H, Riker WL, Idriss FS. Surgical management of vas16. Mustard WT, Trimble AW, Trusler GA. Mediastinal vascular cular rings. Arch Surg 1972; 105:327-333. anomalies causing tracheal and esophageal compression and 9. Fleming WH, Umstott CE, Symbass PW, et al. The embryology obstruction in childhood. J Can Med Assoc 1962: 87:1301. and management of vascular rings. Southern Med J 1976; 17. Gumbiner CM, Mullins CE, McNamara DG. Pulmonary artery 69:878-880. sling. Am J Cardiol 1980; 45:311-315. 10. Binet JP, Langloid J. Aortic arch anomalies in children and in18. Castanada AR. Pulmonary artery sling. Ann Thorac Surg 1979; fants. J Thorac Cardiovasc Surg 1977; 73:248-252. 28:210-211. 11. Berman W Jr, Yabek SM, Dillon T, et al. Vascular ring due to 19. Sade RM, Rosenthal A, Fellows K, Castenada AR. Pulmonary left aortic arch and right descending aorta. Circulation 1981; artery sling. J Thorac Cardiovasc Surg 1975; 69:333. 63:458-460.
