Carl L. Backer1, Cynthia K. Rigsby2, and Constantine Mavroudis3 1UK Healthcare Kentucky Children’s Hospital, Lexington, KY, USA 2Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, USA 3Peyton Manning Children’s Hospital, Indianapolis, IN, USA The term “vascular ring” is used to describe vascular anomalies that result from abnormal development of the arteries of the embryonic pharyngeal arches and cause compression of the trachea, esophagus, or both. The first vascular ring described was a double aortic arch by Hommel in 1737 [1]. The phrase “vascular ring” was introduced to the surgical literature by Robert E. Gross in 1945 [2]. At that time he reported the first successful division of a double aortic arch causing tracheal obstruction in a 1‐year‐old infant: “A ring of blood vessels was found encircling the intrathoracic portion of the esophagus and trachea.” Most children with vascular rings present with symptoms in the first few months of life and require surgery within the first year of life [3]. Some of these anomalies are anatomically complete rings, or true vascular rings. Others are anatomically incomplete, or partial vascular rings, but present similar symptoms because of the tracheoesophageal compression. In particular, the pulmonary artery sling is a rare vascular anomaly in which the left pulmonary artery originates from the right pulmonary artery and encircles the right main stem bronchus and distal trachea before entering the hilum of the left lung. This anomaly was first reported by Glaevecke and Doehle in 1897 as a postmortem finding in a 7‐month‐old infant with severe respiratory distress [4]. The classification of vascular rings we have used at Ann & Robert H. Lurie Children’s Hospital of Chicago is based on anatomic features, particularly the location of the aortic arch(es). This classification scheme was endorsed by the Congenital Heart Surgery International Nomenclature and Database Project for the Society of Thoracic Surgeons database [5]. The history of vascular ring surgery began with the division of a double aortic arch by Gross at Boston Children’s Hospital on June 9, 1945 [2]. Gross was also the first to describe the other common true vascular ring – the right aortic arch with a retroesophageal left subclavian artery and a left ligament [2]. Finally, Gross was the first, in 1948, to suspend the innominate artery to the posterior aspect of the sternum to alleviate compression of the trachea by the innominate artery [6]. The first repair of a pulmonary artery sling was by Willis J. Potts at Children’s Memorial Hospital in Chicago in 1953 [7]. More recently, for the complex subset of patients with pulmonary artery sling who also have tracheal stenosis from complete tracheal rings, the pericardial patch tracheoplasty technique was first performed by Farouk S. Idriss in 1982 [8]. The first tracheal autograft for tracheal stenosis also was performed at Children’s Memorial Hospital [9]. Since Potts’s first operation on an infant with double aortic arch at our institution on July 27, 1946 [10], we have operated on over 500 patients with different types of vascular tracheoesophageal compression syndromes. It is this experience that forms the basis for this chapter (Table 12.1). In 1922 Congdon [11] reported his extensive experience with the study of the embryonic development of the human pharyngeal arches. Based on these descriptions, Edwards [12] proposed a schematic model with a double aortic arch system and bilateral persistence of the arterial duct. More recently, Stewart and associates [13] summarized the pathologic, embryologic, and roentgenographic correlations of these lesions. In embryonic vascular development six pairs of aortic arches connect the primitive ventral and dorsal aortas (Figure 12.1). It should be noted that the existence of the fifth arch remains somewhat contentious [14]. The formation of a vascular ring depends on the preservation or deletion of specific segments of the rudimentary embryonic arch arteries, specifically the arteries of the fourth and sixth arches. Most portions of the first and second arch arteries regress, while the fifth arch arteries, as stated, remain contentious entities. The arteries of the third arches become the carotid arteries. The right and left pulmonary arteries develop within the pharyngeal mesenchyme, and take their origin from the base of the aortic sac. In normal development, the right sixth arch artery disappears, while on the left side it persists to become the arterial duct. The left fourth arch artery becomes the transverse aortic arch, while the right fourth arch artery remodels to become the base of the brachiocephalic artery. The seventh intersegmental arteries arise from the dorsal aorta and remodel to form the subclavian arteries. Normally, the dorsal part of the right fourth arch involutes, leaving the usual left aortic arch configuration (Figure 12.1). The “sidedness” of the aortic arch is dependent on whether the apex of the aortic arch is on the right or left side of the trachea. Table 12.1 Vascular ring patients operated on at Ann & Robert H. Lurie Children’s Hospital of Chicago: 1946–2018. If the dorsal components of both the right and left fourth arches persist, then a double aortic arch is formed (Figure 12.1). Two arches arise from the ascending aorta and pass on both sides of the trachea and esophagus, joining the descending aorta and producing a true ring. Each arch gives rise from its cranial aspect to carotid and subclavian arteries. In 85% of these infants, it is the right‐sided arch that is dominant, with the left arch dominant in 5%, and the arches being of nearly equal size in the remainder. The trachea and esophagus are encircled and compressed by the two arches. In a small number of patients the distal left aortic arch will arise from a Kommerell diverticulum [15]. Depending on the exact site(s) of interruption of the left aortic arch, and the branching pattern to the left subclavian artery, left carotid artery, and arterial duct, there are various configurations for a right aortic arch (Figure 12.2). The two common variations are retroesophageal left subclavian artery, found in two‐thirds of cases, and mirror‐image branching in the remaining third. The right aortic arch with a retroesophageal left subclavian artery results from persistence of the right fourth arch, and deletion of the left arch between the left carotid and subclavian arteries. The subclavian artery originates from the descending aorta, and courses to the left behind the esophagus. The arterial ligament extends from the descending aorta to the left pulmonary artery, completing the vascular ring (Figure 12.2A). Figure 12.1 (A–D) Diagram of the embryonic aortic arches. Six pairs of aortic arches originally develop between the dorsal and ventral aorta. The first, second, and fifth arches regress. Preservation or deletion of different segments of the rudimentary arches results in either a double aortic arch, a right aortic arch, or the “normal” left aortic arch. Ao, aorta; CCA, common carotid artery; L, left; PA, pulmonary artery; R, right; SA, subclavian artery. Source: Reproduced by permission from Backer CL, Mavroudis C, in Pediatric Cardiac Surgery, 3rd ed., Philadelphia, PA: Mosby; 2003, pp. 234–250. A right aortic arch with mirror‐image branching and left‐sided arterial ligament results from persistence of the right fourth aortic arch and disappearance of the left arch between the subclavian artery and the dorsal descending aorta. When the ligament originates from the descending aorta, a complete vascular ring is formed (Figure 12.2B) [16]. If the ligament originates from the brachiocephalic artery, which is more common in this group, a vascular ring is not formed and the child is asymptomatic (Figure 12.2C) [15]. Although one‐third of patients with tetralogy of Fallot and common arterial trunk have a right aortic arch [17], we did not find a reverse association with a specific cardiac defect when a vascular ring was formed by a right aortic arch. Figure 12.2 Right aortic arch types. (A) Retroesophageal left subclavian artery, ligamentum to descending aorta. (B) Mirror‐image branching, ligamentum to descending aorta. (C) Mirror‐image branching, ligamentum to left innominate artery. Ao, aorta; CCA, common carotid artery; L, left; M, main; PA, pulmonary artery; R, right; SA, subclavian artery. Source: Reproduced by permission from Backer CL, Mavroudis C, in Pediatric Cardiac Surgery, 3rd ed., Philadelphia, PA: Mosby; 2003, pp. 234–250. The embryonic origin of pulmonary artery sling occurs when the developing left lung captures its arterial supply through capillaries forming caudad rather than cephalad to the developing tracheobronchial tree [18]. The left pulmonary artery then originates from the right pulmonary artery instead of the pulmonary trunk. The left pulmonary artery passes around the right main bronchus and courses between the trachea and esophagus, forming a “sling” that compresses the tracheobronchial tree (Figure 12.3). The airway may also be compromised by associated complete cartilage tracheal rings, the so‐called ring‐sling complex, where the membranous portion of the trachea is absent and the tracheal cartilages are circumferential [19]. This syndrome results from anterior compression of the trachea by the innominate, or brachiocephalic, artery [20]. Why this artery, which normally crosses in front of the trachea, should compress the trachea in some cases and not others is not well understood. The artery appears to originate somewhat more posteriorly and leftward on the aortic arch than usual. As the artery courses to the right, upward, and posterior to reach the right thoracic outlet, it compresses the trachea anteriorly (Figure 12.4). Figure 12.3 Pulmonary artery sling. Inset: Left lateral view of anterior compression of the esophagus of anterior trachea. L, left; M, main; PA, pulmonary artery; R, right. Source: Reproduced by permission from Backer CL, Mavroudis C, in Pediatric Cardiac Surgery, 3rd ed., Philadelphia, PA: Mosby; 2003, pp. 234–250. Figure 12.4 Innominate artery compression of anterior trachea. Ao, aorta; PA, pulmonary artery. Source: Reproduced by permission from Backer CL, Mavroudis C, in Pediatric Cardiac Surgery, 3rd ed., Philadelphia, PA: Mosby; 2003, pp. 234–250. A left aortic arch with aberrant right subclavian artery develops when the artery of the right fourth arch regresses between the origins of the subclavian and carotid arteries. The right subclavian artery, originating from the seventh cervical intersegmental artery, traverses the mediastinum and inserts on the descending aorta. The right subclavian artery then becomes a branch of the descending aorta, and courses to the right, posterior to the esophagus. This produces an indentation of the esophagus, but does not form a complete vascular ring (Figure 12.5). This is the most common vascular anomaly of the aortic arch system, being found in 0.5–0.9% of all individuals [21, 22]. Because it is so common, it has been blamed in the past, mistakenly, for vague swallowing symptoms, earning the label “dysphagia lusoria” [23] or “difficulty in swallowing due to a trick of nature.” The aberrant right subclavian is actually nearly always a “red herring” and not the true etiology of the symptoms [24]. There are a few rare cases, however, where division of the right subclavian artery has resulted in resolution of dysphagia [25]. Figure 12.5 Left aortic arch with aberrant right subclavian artery causing posterior compression of the esophagus. Ao, aorta; CCA, common carotid artery; L, left; PA, pulmonary artery; R, right; SA, subclavian artery. Source: Reproduced by permission from Backer CL, Mavroudis C, in Pediatric Cardiac Surgery, 3rd ed., Philadelphia, PA: Mosby; 2003, pp. 234–250. In the unusual combination of left aortic arch and right descending aorta, if there is persistently patent right‐sided arterial duct or ligament, then a vascular ring is formed [26]. The left aortic arch in these cases is nearly always a cervical arch, resulting from persistence of the artery of the third rather than the fourth embryonic pharyngeal arch [27]. A large sweeping cervical arch may independently compress the trachea anteriorly, even in the absence of a right‐sided arterial duct. This combination is one of the very few vascular rings that are best approached with a right rather than a left thoracotomy [28]. These patients are very rare, and often have associated cardiac anomalies [29]. Because we now obtain a computed tomographic (CT) or magnetic resonance image (MRI) on all patients suspected of having vascular rings prior to an operation, the exact anatomy and decision about the approach have become less of an “art” [30]. A single case report has described an arterial duct traveling from the right pulmonary artery to the descending aorta between the trachea and esophagus with an aberrant right subclavian artery, producing the so‐called arterial ductal sling [31]. The duct was compressing the trachea and right bronchus in a manner analogous to pulmonary artery sling. We reported a 5‐month‐old infant with a right aortic arch, right‐sided arterial ligament, and absent left pulmonary artery who required division of the right ligament to relieve respiratory failure [32]. Robotin and colleagues [33] reported three groups of unusual forms of tracheobronchial compression in a series of over 500 patients with vascular rings. Three patients had an encircling right aortic arch with a left‐sided descending aorta and ligament, giving a so‐called circumflex aorta [34]. In two patients, airway compression was the consequence of a pincer effect between a malposed and enlarged ascending aorta and the descending aorta. In another three patients, airway compression was encountered after an arterial switch. Van Son [35] reviewed two patients with a right cervical aortic arch, while McElhinney [36] reviewed six such patients. Another rare vascular ring occurs in the setting of a mirror‐image arrangement, with a left aortic arch with an aberrant right subclavian artery, and a right‐sided arterial ligament. These patients, and we have had one, require a right thoracotomy and division of the right‐sided ligament. Most children with vascular rings present with symptoms within the first several weeks to months of life. The symptoms typically include some combination of respiratory distress, stridor, the classic “seal bark” cough, apnea, dysphagia, and recurrent respiratory tract infections (Table 12.2) [30]. Some older children will present only with symptoms of dysphagia or slow feeding, where they tend to be the last child to leave the table because they have to chew their food carefully as a learned procedure. Infants may hold their head hyperextended to splint the trachea and lessen the obstruction, improving their breathing. Apnea or cyanosis may be precipitated by swallowing a bolus of solid food that presses on the soft posterior trachea within the restrictive confines of a ring. Most infants are well nourished, however, because they tolerate liquid formula well. When they are advanced to solid food, symptoms become more evident. The diagnosis of vascular rings requires a high index of suspicion, because of the relative infrequency of this diagnosis compared with other conditions that cause respiratory distress in children such as asthma, reflux, and upper respiratory tract infection. Symptoms appear earlier and tend to be more severe in cases with a double aortic arch. A simple “cold” may precipitate severe respiratory difficulty. Children with the innominate artery compression syndrome present with symptoms of tracheal compression, and nearly one‐half have had apneic episodes. It is of importance in these infants to rule out other causes of apneic spells. This includes a complete neurologic evaluation, investigation for gastroesophageal reflux, and sleep studies. Physical examination may reveal stridor, wheezing, tachypnea, a brassy cough, or noisy breathing. If the obstruction is severe, there may be obvious subcostal retractions and nasal flaring. The number of patients presenting with various symptoms in our series of vascular ring patients is shown in Table 12.1. Table 12.2 Symptoms leading to clinical presentation in patients with vascular rings*. * More than one symptom occurred in many patients. †Our records did not provide symptoms for the earlier patients in the series. Source: Adapted from Backer CL et al. J Thorac Cardiovasc Surg. 2005;129:1339–1347. The diagnosis of a vascular ring starts with the plain chest radiograph. There are a myriad of other diagnostic procedures that may be employed. These include barium esophagogram, bronchoscopy, tracheograms, CT, MRI, echocardiography, and cardiac catheterization. The emphasis should be to arrive at a diagnosis with the most efficient use of the multiple tests available. Once the diagnosis has been made, further studies are not required and the clinician should resist the tendency to obtain more studies that simply continue to confirm the diagnosis in a slightly different way. The evaluation of a child with a possible vascular ring begins with anteroposterior and lateral chest radiography [37]. The mediastinum should be evaluated for a left aortic arch, right aortic arch, or double aortic arch, as determined by the location of the aortic arch in relation to the trachea. When the location of the arch is not clear, a double aortic arch should be suspected. The lateral chest radiograph should be carefully evaluated for tracheal narrowing at the level of the aortic arch. If a right aortic arch or double aortic arch is suspected or narrowing of the trachea is seen on lateral images, further investigation for a vascular ring should be initiated. Unilateral hyperinflation of the right lung suggests a pulmonary artery sling. The barium esophagogram was historically the most widely used study for the diagnosis of vascular rings [38]. This is no longer the case and barium swallow has been supplanted by CT and MRI [30, 39, 40]. The impressions produced in the barium‐filled esophagus by the anomalous aortic arch and/or branches often are quite characteristic for each lesion and may allow strong suspicion of the specific ring type present. A double aortic arch or right aortic arch with left ligamentum will appear as a deep persistent extrinsic indentation on the posterior aspect of the esophagus (Figure 12.6). Bilateral persistent compressions of the esophagus on the anteroposterior views are usually present with a double aortic arch (Figure 12.7) [3]. The dominant arch is usually on the right, higher, and more posterior than the lesser arch. A right aortic arch and retroesophageal left subclavian artery will produce an oblique indentation angled toward the left shoulder. A high posterior oblique indentation directed from left to right on the esophagogram is indicative of an aberrant right subclavian artery. A pulmonary artery sling is suggested by an anterior indentation of the esophagus (Figure 12.8). The diagnosis of a complete vascular ring can usually be established with some level of certainty with a barium esophagogram. Determining the specific type of ring with a chest radiograph and esophagogram alone, however, is not usually possible. Although historically surgeons would operate on these patients with only a barium swallow and a chest x‐ray, we currently recommend CT or MRI imaging on all vascular ring patients prior to surgical intervention [30]. Figure 12.6 Lateral esophagogram of an 11‐month‐old boy with a double aortic arch, right arch dominant. Arrow points to the deep posterior indentation in the esophagus caused by the right arch. Source: Reproduced by permission from Backer CL, Mavroudis C, in Pediatric Cardiac Surgery, 3rd ed., Philadelphia, PA: Mosby; 2003, pp. 234–250. Figure 12.7 Anteroposterior esophagogram of a 4‐month‐old boy who presented with stridor and was found to have a double aortic arch (arrows). Source: Reproduced by permission from Backer CL et al. J Thorac Cardiovasc Surg. 1989;97:725. CT scanning is very accurate in the identification of vascular anomalies of the aortic arch and great vessels. It is our preferred diagnostic method [30, 39]. A double aortic arch is diagnosed with certainty when both limbs are patent and enhanced with the intravenous administration of contrast material. In some cases, the vascular ring may be completed by a nonenhanced segment, either an arterial ligament or an atretic portion of the lesser arch. In these cases, the diagnosis of a complete ring depends on recognizing the arterial branching pattern, the side of the aortic arch, and focal narrowing of the airway. Three‐dimensional reconstruction of the vascular structures establishes a very clear “roadmap” for the surgeon (Figure 12.9). Figure 12.8 Lateral esophagogram of a 18‐month‐old girl with repeated episodes of stridor and respiratory tract infections. Arrow points to anterior indentation of esophagus caused by the anomalous left pulmonary artery. Source: Reproduced by permission from Backer CL, Mavroudis C, in Pediatric Cardiac Surgery, 3rd ed., Philadelphia, PA: Mosby; 2003, pp. 234–250. Figure 12.9 Three‐dimensional reconstruction of computed tomography scan. Posterior view of a child with fetal diagnosis of a vascular ring. Patient has a double aortic arch, right arch dominant, left arch smaller but patent. Vessels are shown in red, trachea and bronchi ghosted in blue. Figure 12.10 The same patient as in Figure 12.9, visualized from above. The smaller left arch was divided just proximal to the insertion into the descending aorta. One clue to an arch anomaly is the “four‐artery sign,” which can be seen on sections obtained cephalad to the aortic arch. It consists of two dorsal subclavian arteries and two ventral carotid arteries evenly spaced around the trachea [41]. The sign is present when the two dorsal subclavian arteries arise directly from the aortic arch, and not from a brachiocephalic artery. This occurs with double aortic arches and configurations with aberrant subclavian arteries (Figure 12.10). In patients with innominate artery compression syndrome, CT scan with contrast will show the anterior compression of the trachea, and helps to confirm the visual impression at the time of bronchoscopy (Figure 12.11). In children with a pulmonary artery sling, CT demonstrates the left pulmonary artery originating from the right pulmonary artery, encircling the trachea, and coursing to the hilum of the left lung anterior to the esophagus and aorta (Figure 12.12). In addition, the presence of associated complete tracheal rings can be seen, and the extent of the tracheal narrowing can be used to plan the surgical approach. MRI is well suited for imaging vascular structures of the mediastinum (Figures 12.13 and 12.14) [3, 42, 43]. Axial images provide the same information as CT without ionizing radiation or the need for intravenously administered contrast material. In addition, coronal and sagittal sections or images can be helpful in confusing cases. As with CT, the diagnosis of a vascular ring is based on the vascular branching pattern, the side of the aortic arch or arches, and narrowing of the airway. Unfortunately, like CT, MRI cannot reveal a small ligament or atretic segment. A disadvantage to MRI is the length of time required for the study, necessitating sedation. When there is significant respiratory distress, sedation may not be safe. It seems that more often than not, the quality of MRI studies is poorer than CT scans because of patient movement. Sedation is rarely necessary with CT since in a restrained infant dynamic scanning can be performed quickly. Because of these issues CT remains our imaging modality of choice. Both CT and MRI also can be helpful by revealing unsuspected mediastinal or tracheobronchial abnormalities. Figure 12.11 Computed tomographic scan with contrast of an infant with innominate artery compression syndrome. The superior cut shows a normal size trachea (arrow). The inferior cut shows the trachea (arrow) compressed by the innominate artery. Source: Reproduced by permission from Backer CL, Mavroudis C, in Pediatric Cardiac Surgery, 3rd ed., Philadelphia, PA: Mosby; 2003, pp. 234–250. Figure 12.12 Pulmonary artery sling. (A) Axial computed tomography image of a 6‐week‐old 3.5 kg infant with pulmonary artery sling and complete tracheal rings. The left pulmonary artery originates from the right pulmonary artery and encircles the distal stenotic trachea. Note the course of the left pulmonary artery anterior to the descending aorta. (B) Three‐dimensional reconstruction of the main, right, and left pulmonary arteries. Note narrowing of the left pulmonary artery caused by external compression. Bronchoscopy is often employed in children with respiratory distress who do not have a definite diagnosis [44]. External compression of the trachea just above the carina suggests either a double aortic arch or a right aortic arch with left ligament. The initial diagnosis of innominate artery compression is nearly always made with bronchoscopy. In these patients, bronchoscopy classically shows a pulsatile anterior compression of the trachea extending from left to right at a location closer to the vocal cords than true vascular rings (Figure 12.15). Indication of significant compression occurs only when its extent is more than 70–80% of the lumen of the trachea. Anterior compression of this area with the tip of the bronchoscope, while monitoring the right radial pulse, is a useful diagnostic maneuver, with resultant obliteration or weakening of the pulse. Bronchoscopy can also be used to rule out other causes of respiratory distress, such as aspiration of a foreign body or subglottic stenosis. In cases of pulmonary artery sling, bronchoscopy is required to assess for associated complete tracheal rings. In all cases an extreme degree of caution is necessary during and after bronchoscopy as the tracheal lumen, already narrowed by the vascular compression, may be compromised further by edema from bronchoscopic manipulation. We obtain bronchoscopy in all patients with a vascular ring prior to surgical repair because of the 3–5% incidence of unsuspected tracheal pathology and to assess prognosis of associated tracheobronchomalacia [30].
CHAPTER 12
Vascular Rings and Pulmonary Artery Sling
Embryology and Pathology
Complete vascular rings
Double aortic arch
187
Right aortic arch with left ligament
217
Partial vascular rings
Innominate artery compression syndrome
88
Pulmonary artery sling
47
Left aortic arch, aberrant right subclavian artery
7
Total
546
Double Aortic Arch
Right Aortic Arch
Pulmonary Artery Sling
Innominate Artery Compression
Aberrant Right Subclavian Artery
Rare Vascular Rings
Clinical Presentation and Diagnosis
Double aortic arch
(n=80)†
Right aortic arch
(n=78)†
Stridor
46 (57%)
18 (23%)
Recurrent upper respiratory
tract infections
22 (27%)
18 (23%)
Cough
17 (21%)
8 (10%)
Dysphagia
12 (15%)
12 (15%)
Respiratory distress
8 (10%)
13 (17%)
Ventilator preoperatively
7 (9%)
3 (4%)
Chest Radiograph
Barium Esophagogram
Computed Tomography
Magnetic Resonance Imaging
Bronchoscopy
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