Vascular rings and pulmonary artery sling (PAS) represent 1 to 3 percent of all congenital cardiac malformations. The most frequent type of vascular ring is aberrant left subclavian artery, whereas the most rare condition is the PAS.
Of the over 100 variations in morphology that have been described, 6 are most commonly observed: (1) anomalous left subclavian artery with left aortic arch, (2) double aortic arch (DAA), (3) right aortic arch with left ligamentum, (4) right aortic arch with aberrant left subclavian artery, (5) tracheal compression by the innominate artery, and (6) PAS. Cardiac malformations (tetralogy of Fallot, ventricular septal defect, atrial septal defect, and aortic coarctation) are seen in 15 to 20 percent of cases.
Structural obstruction of the aerodigestive tract
Most vascular rings are symptomatic. Compression by the complete or partial ring of the esophagus, trachea, or both dictates the mode of presentation. Patients with an aberrant left subclavian artery are often asymptomatic, whereas pulmonary artery sling and complete rings are almost uniformly clinically significant.
Chest x-ray is rarely diagnostic. Barium esophagography is usually able to point to the presence of a vascular ring with reasonable specificity. Computed tomography (CT) and magnetic resonance imaging (MRI) are useful in defining the anatomy and are currently more routinely utilized. Bronchoscopy is important in the diagnosis of both innominate artery compression and PAS and in assessing the degree of tracheobronchomalacia.
Treatment is indicated in all symptomatic patients. With the exception of DAA with dominant left component, almost all cases (left aortic arch with right ligamentum, PAS, and innominate artery compression) are approached through a left thoracotomy with division of the vascular ring.
For the vast majority of vascular rings, morbidity and mortality are the same as seen in any simple thoracic procedure involving a thoracotomy. Mortality is much higher for patients with PAS. The degree of tracheobronchomalacia has a significant impact on long-term prognosis.
Introduction and Definitions
Vascular rings are congenital abnormalities of the aortic arch system that cause tracheal and esophageal compression. Patients with vascular rings have varying degrees of symptoms that range from subtle swallowing difficulties in the adolescent to severe respiratory distress in the neonate. The symptoms depend on the tightness of the vascular ring as it compresses the esophagus and/or trachea. The phrase “pulmonary artery sling (PAS)” refers to a particular anomaly where the left pulmonary artery (PA) originates from the right PA and compresses the distal trachea and right bronchus on its route to the left lung. The Congenital Heart Surgery Nomenclature and Database Project Committee has standardized the classification of vascular rings to include complete rings [double aortic arch (DAA), right aortic arch with left ligamentum] and incomplete rings [pulmonary artery sling (PAS), innominate artery compression].1 Each of these vascular rings can have different anatomic variations. Nearly all patients with complete vascular rings and PAS will eventually require surgical intervention. Although the literature now contains citations describing over 100 variations of vascular rings, in this chapter we will focus on the most common vascular rings. We will also address the issue of a Kommerell diverticulum and select rare vascular rings. We will review the historic surgical events in vascular ring surgery, the epidemiology, embryology, pathogenesis, the clinical presentations and diagnostic evaluations, the surgical management, and postoperative care and outcomes.
The first vascular ring described in the medical literature involved a patient with a DAA described by Hommel in 1737.2 The first surgical repair of a vascular ring was performed by Robert Gross on a patient with a DAA in 1945.3 In his report, Gross coined the term “vascular ring.” Gross also reported the first repair of a right aortic arch with left ligamentum, and innominate arteriopexy for innominate artery compression syndrome.4 Willis J. Potts from Children’s Memorial Hospital (Chicago) was the first to successfully repair a PAS in 1953.5
Because some patients with vascular rings fail to manifest symptoms, the exact prevalence of this anomaly is not truly known. In one comprehensive series, the estimate ranged from 0.04 to 0.5 percent of live births or approximately 1 to 3 percent of surgical congenital cardiovascular anomalies.6 The most common vascular anomaly is left aortic arch with an aberrant (retroesophageal) right subclavian artery (not a complete vascular ring) with a prevalence of 0.5 percent.7 In a comprehensive cardiovascular screening program using echocardiography in school-age children, Chen and colleagues reported the following incidence of vascular rings in 186,213 screened children: PA sling (n = 11, 0.006 percent), anatomically complete vascular ring (DAA, right aortic arch with left ligamentum, n = 96, 0.05 percent).8,9
Embryology and Pathogenesis
There is a fascinating and surgically important relationship between the embryology and clinical anatomy of vascular ring anomalies. The characterization of the embryonic arch system by Edwards is based on a hypothetical intermediate stage involving an initial DAA in all patients that progresses in most cases to a single arch system (Fig. 84-1).10 Initially, an aortic arch is located on either side of the trachea with a ductus arteriosus on each side. In this system, early in development six pairs of arches are present that connect the ventral and dorsal aorta. During further development, these arches variously mature, recede, fuse, and remodel to eventually form the typical left-sided aortic arch. Different vascular rings form when specific segments of the aortic arches either persist or resorb. During normal development, most of the first, second, and fifth arches regress, and the third arch persists to become the carotid artery. The right fourth arch forms the right brachiocephalic artery. The left fourth aortic arch becomes the ascending aorta and transverse aortic arch. The fifth aortic arch regresses on each side. In the typical left arch patient, the right dorsal portion of the sixth arch regresses, and on the left side it persists as the ductus arteriosus. The PA forms from a branch of the ventral bud of the sixth aortic arch which connects to the lung bud. The seventh intersegmental artery matures into the subclavian artery. The sidedness of the aortic arch is determined by which fourth arch persists which usually is the left. The anatomic definition of a left arch is that the apex of the aortic arch is to the left of the trachea. With reference to the center of the vertebral bodies, the descending aorta may be either right, left, or midline.
Embryonic arotic arch development. Diagram of the embryonic aortic arches with six pairs of aortic arches originally developing between the dorsal and ventral aorta. During development, the first, second, and fifth arches regress. Preservation or deletion of different segments of the other 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. (Reprinted with permission from Mavroudis C. Pediatric Cardiac Surgery, 3rd edition. Philadelphia: Mosby Elsevier, 2003.)
Double Aortic Arch
A DAA forms when the ascending aorta arises normally from the heart but as it exits the pericardium, the right and left arches both persist and encircle the esophagus and trachea (Figs. 84-2 and 84-3). The left aortic arch passes anterior to the trachea and connects to the descending aorta at the level of the ligamentum arteriosum, while the right aortic arch courses posteriorly to the trachea and esophagus and then joins the descending aorta. The right arch typically gives rise to the right carotid and right subclavian arteries; the left subclavian and carotid arteries originate from the left aortic arch. In our series the right-sided (posterior) arch was dominant in 75 percent of patients with a DAA, the left-sided (anterior) arch was dominant in 18 percent of the patients, and the arches were equal in size in 7 percent of the patients.11
Double aortic arch. Autopsy specimen of a child with a double aortic arch (left arch dominant). Desc. Ao, descending aorta; E, esophagus; LAA, left aortic arch; LCC, left common carotid; LSC, left subclavian; PT, pulmonary trunk; RAA, right aortic arch; RCC, right common carotid; RSA, right subclavian artery; T, trachea. (Courtesy of Diane Spicer from the F.S. Idriss Registry, Children’s Memorial Hospital, Chicago, IL.)
Double aortic arch. This is an illustration of a dominant right arch with a smaller but patent left arch with separate origins of the right and left carotid and subclavian arteries. (RCA, right carotid artery, RSA, right subclavian artery, LCA, left carotid artery, LSA, left subclavian artery, MPA, main pulmonary artery.) (From Backer CL, Mavroudis C, Stewart RD, Holinger LD. Congenital anomalies: Vascular rings. In: Patterson GA, Cooper JD, Deslauriers J, Lerut AE, Luketich JD, Rice TW (eds). Pearson’s Thoracic and Esophageal Surgery. Philadelphia: Churchill Livingstone Elsevier, 2008:242–255.)
Right Aortic Arch with Left Ligamentum
A right aortic arch (RAA) occurs when the left fourth arch involutes and the right fourth arch persists. The two anatomic types of right aortic arch are classified based on the branching pattern of the arch vessel as: retroesophageal left subclavian artery (Fig. 84-4) and mirror-image branching (left brachiocephalic artery) (Fig. 84-5).12 In our series this distribution was 66 percent retroesophageal left subclavian artery and 34 percent mirror-image branching.11 A complete vascular ring occurs when the ligamentum arteriosum connects the descending thoracic aorta to the PA. The vascular ring configuration includes the right aortic arch, the PA, and the ligamentum. In the patient with a retroesophageal left subclavian artery, the ligamentum arteriosum nearly always comes from the descending aorta, completing the vascular ring. In the patient with mirror-image branching, the ligamentum arteriosum may arise either from the descending thoracic aorta or the anterior left brachiocephalic artery. If the ligamentum arises from the left brachiocephalic artery a vascular ring is not formed (Fig. 84-6). This is the common situation in patients with tetralogy of Fallot and truncus arteriosus.
Right aortic arch, left ligamentum, retroesophageal left subclavian artery. The vascular ring is formed by the right aortic arch, the main pulmonary artery, and the ligamentum arteriosum (RCA, right carotid artery; RSA, rigth subclavian artery; LCA, left carotid artery; LSA, left subclavian artery; MPA, main pulmonary artery). (From: Backer CL, Mavroudis C, Stewart RD, Holinger LD. Congenital anomalies: Vascular rings. In: Patterson GA, Cooper JD, Deslauriers J, Lerut AE, Luketich JD, Rice TW (eds). Pearson’s Thoracic and Esophageal Surgery. Philadelphia: Churchill Livingstone Elsevier, 2008:242–255.)
Right aortic arch, left ligamentum, mirror-image branching (Note left innominate artery). The vascular ring is formed by the same components as in Figure 84-3, but the left subclavian artery has an anterior origin from the left innominate artery. (RCA, right carotid artery; RSA, right subclavian artery; LCA, left carotid artery; LSA, left subclavian artery; MPA, main pulmonary artery; Innominate A, innominate artery.) (From Backer CL, Mavroudis C, Stewart RD, Holinger LD. Congenital anomalies: Vascular rings. In: Patterson GA, Cooper JD, Deslauriers J, Lerut AE, Luketich JD, Rice TW (eds). Pearson’s Thoracic and Esophageal Surgery. Philadelphia: Churchill Livingstone Elsevier, 2008:242–255.)
Right arch, mirror-image branching with ligamentum from innominate artery. There is a space between the ligamentum and descending aorta and a vascular ring is not formed. (RCA, right carotid artery; RSA, right subclavian artery; LCA, left carotid artery; LSA, left subclavian artery; MPA, main pulmonary artery; Innominate A, Innominate artery.) (From Backer CL, Mavroudis C, Stewart RD, Holinger LD. Congenital anomalies: Vascular rings. In: Patterson GA, Cooper JD, Deslauriers J, Lerut AE, Luketich JD, Rice TW (eds). Pearson’s Thoracic and Esophageal Surgery. Philadelphia: Churchill Livingstone Elsevier, 2008:242–255.)
Innominate Artery Compression
Innominate artery compression results when the anterior trachea is depressed by the innominate artery as it travels from left to right within the superior mediastinum. The exact mechanism that causes the aortic compression in some patients is unknown but may involve a more distal takeoff of the innominate artery from the aorta or a predisposition to tracheomalacia. Figures 84-7–84-9 show by computed tomography (CT) imaging how the tracheal lumen can be compressed in a 5-month old with severe stridor from innominate artery compression syndrome.
Innominate Artery Compression Syndrome. Serial CT cuts in a 5-month-old infant with severe stridor. The tracheal lumen completely disappears in the second of the three images. By bronchoscopy the lumen was nearly occluded. The child responded very well to innominate arteriopexy. (From Backer CL, Mavroudis C, Stewart RD, Holinger LD. Congenital anomalies: Vascular rings. In: Patterson GA, Cooper JD, Deslauriers J, Lerut AE, Luketich JD, Rice TW (eds). Pearson’s Thoracic and Esophageal Surgery. Philadelphia: Churchill Livingstone Elsevier, 2008:242–255.)
Pulmonary Artery Sling
PAS occurs when two embryologic abnormalities coexist at the same time. The left PA originates from the right sixth arch instead of the left sixth arch and the course of the left PA is posterior rather than anterior to the maturing tracheobronchial tree. The anatomic result is that the left PA originates from the posterior aspect of the right PA and not from the main PA (Fig. 84-10). The left PA then courses posteriorly over the right main stem bronchus and then between the trachea and esophagus which results in a sling compressing the right main stem bronchus and the posterior distal trachea. The ductus or ligamentum originates from the usual site on the main PA and connects to the aorta. A true vascular ring does not exist but the “sling” causes significant symptomatic compression. There is a strong association between PAS and complete cartilage tracheal rings causing tracheal stenosis.13
Pulmonary artery sling. The aorta has been cut away to visualize the right pulmonary artery and the anomalous origin of the left pulmonary artery from the rigth pulmonary artery. The left pulmonary artery courses posterior to the trachea, anterior to the esophagus, and anterior to the descending thoracic aorta on its way to the left lung. (RCA, right carotid artery; RSA, right subclavian artery; RPA, right pulmonary artery; LCA, left carotid artery; LSA, left subclavian artery; MPA, main pulmonary artery; Innominate A = Innominate artery.) (From Backer CL, Mavroudis C, Stewart RD, Holinger LD. Congenital anomalies: Vascular rings. In: Patterson GA, Cooper JD, Deslauriers J, Lerut AE, Luketich JD, Rice TW (eds). Pearson’s Thoracic and Esophageal Surgery. Philadelphia: Churchill Livingstone Elsevier, 2008:242–255.)
Aberrant Right Subclavian Artery with a Left Aortic Arch
This lesion is not a true vascular ring but is the most common vascular arch anomaly, occurring in 0.5 percent of all humans (Fig. 84-11).7,14 In this anomaly the aortic arch and descending thoracic aorta are left-sided, and there is no right brachiocephalic artery present. The right subclavian artery arises independently from the descending thoracic aorta and traverses the mediastinum posterior to the esophagus en route to the right arm. This lesion in fact rarely (if ever) causes symptoms and surgical intervention for these patients is uncommon.15 We have not operated on a patient with this diagnosis since 1973. What frequently occurs is that, during the evaluation of a patient with swallowing symptoms, an aberrant right subclavian artery is discovered and mistakenly considered as the etiology of the swallowing symptoms. That is why this is referred to as “dysphagia lusoria” which refers to difficulty in swallowing due to a “trick of nature.”15 The aberrant right subclavian artery and swallowing difficulties are “true, true, and unrelated.” The exception to the usual recommendation of no surgical intervention is the older patient with aneurysmal dilation of the origin of the right subclavian artery, a Kommerell diverticulum.16 These patients may indeed require Kommerell diverticulum resection and right subclavian artery reimplantation, usually in the older adult patient.17
Aberrant right subclavian artery. This illustration is a right subclavian artery originating from the descending thoracic aorta distal to the take-off of the left subclavian artery. This artery courses in the posterior mediastinum posterior to the esophagus as it travels to the rigth arm. (RCA, right carotid artery; RSA, rigth subclavian artery; LCA, left carotid artery; LSA, left subclavian artery; MPA, main pulmonary artery.)(From Backer CL, Mavroudis C, Stewart RD, Holinger LD. Congenital anomalies: Vascular rings. In: Patterson GA, Cooper JD, Deslauriers J, Lerut AE, Luketich JD, Rice TW (eds). Pearson’s Thoracic and Esophageal Surgery. Philadelphia: Churchill Livingstone Elsevier, 2008:242–255.)
Rare Vascular Rings
Since many embryonic variants may exist, there are numerous rare vascular ring anomalies that have been reported.18–22 One rare vascular ring is created by a left aortic arch, right descending thoracic aorta, and a right ligamentum arteriousum.21 A second rare vascular ring involves a right aortic arch, right ligamentum, and an absent left PA.18 Another rare vascular ring is a circumflex aorta that consists of a right aortic arch, a left-sided descending thoracic aorta, and left ligamentum arteriosum.22 In this lesion the problem is posterior compression of the trachea by the aorta crossing from right to left above the carina.
The most commonly associated lesion in patients with vascular rings is congenital heart disease, occurring in 12 percent of patients with vascular rings.11 The most common cardiac lesions are ventricular septal defect and tetralogy of Fallot. The most commonly associated chromosomal abnormality is 22q.11 deletion, which occurs in 15 to 20 percent of patients with associated cardiac defects.23 These additional anomalies can impact the operative strategy, the postoperative recovery period, and the long-term outcome for these patients.