The aortic arch, branch pulmonary arteries, and the ductus arteriosus have a close spatial relationship to the airways and esophagus. Abnormalities of the position or course of these vascular structures can cause obstruction to the major airways or esophagus by external compression.
The true incidence is difficult to estimate, because many cases are asymptomatic, but it has been reported to comprise 1% of all cardiovascular malformations requiring surgical management. Furthermore, a right-sided aortic arch is estimated to occur in 0.1% of the population, and this is associated with an increased risk of a complete vascular ring. Because tracheoesophageal compression can lead to significant morbidity, it should always be considered in a patient with unexplained symptoms of dyspnea or dysphagia. The vast majority of cases are diagnosed in young children, and there is a male preponderance. Although rare in adults, both symptomatic and incidental vascular rings do present in clinical practice and can pose significant challenges. Where direct data in adults are lacking, this chapter has been supplemented by relevant experience in the pediatric population and by morphological studies.
Complications from compression of the airways can be divided into two categories:
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Direct effect of vascular compression on the airway leading to respiratory compromise
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Secondary tracheobronchomalacia and stenoses that result from prolonged compression and degeneration of previously normal cartilage
Normal Embryogenesis
Understanding the normal development of the thoracic vascular system is critical in appreciating the problems that may arise. The aortic arch and pulmonary trunk, together with the main branches, are evolutionally related to the six pairs of arterial arches. These partially encircle the pharynx to connect the ventral aorta to the paired dorsal aortas, which are joined to the future descending aorta. For our purpose, this can be simplified to an embryonic double arch system ( Fig. 42.1A ) as originally proposed by Edwards (see Fig. 42.1B ). Once the third paired arches have developed, the first and second paired arches disappear. The cephalic extension of the ventral and dorsal aorta beyond the fourth arch becomes the common carotid (the portion of the ventral aorta between the third and fourth arches), internal carotid (cephalic extension of the ventral aorta beyond the third arch), and external carotid (third arch and cephalic extension of the dorsal aorta) arteries, respectively, on each side. The dorsal aortas between the third and fourth arches regress. The part of the ventral aorta that is proximal to the fourth arch on the right becomes the brachiocephalic artery (segment D, see Fig. 42.1B ) and on the left it becomes the future aortic arch between the right brachiocephalic artery and the left common carotid artery (LCCA) (segment E, see Fig. 42.1B ). The fourth arch on the left side becomes the future aortic arch between the LCCA and the origin of the future left subclavian artery (LSCA) (segment F, see Fig. 42.1B ), and on the right it forms the origin of the future right subclavian artery (RSCA) (segment C, see Fig. 42.1B ). The fifth paired arches usually disappear but may persist. The lateral portion of the left sixth arch forms the ductus arteriosus, and the medial portions of both sixth arches form the origins of the pulmonary arteries. The seventh intersegmental arteries migrate cephalad to form the future subclavian arteries (see Fig. 42.1A ). Ultimately the spiral septation of the ventral aorta, or common arterial trunk, provides for separation of the pulmonary trunk from the ascending aorta.
In normal development we observe the disappearance of segment A (see Fig. 42.1B ) of the dorsal aorta and distal part of the right sixth arch, whereas the distal part of the left sixth arch persists as the arterial duct ( Fig. 42.2 ), thus giving rise to a left aortic arch.
Classification and Morphology of Individual Lesions
Native Anatomic Anomalies
Congenital malformations of the cardiovascular system are found mainly in neonates and young infants causing dyspnea or dysphagia, or both, depending on the site of obstruction. These rarely present de novo in adults. The classification and morphology of native anatomic anomalies are listed in Box 42.1 .
Native Anatomic Anomalies
Vascular Rings
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Double aortic arch (see Fig. 42.3 )
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Right aortic arch with aberrant left subclavian artery (Ab LSA) and left-sided arterial duct (see Fig. 42.4 )
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Right aortic arch with mirror image branching and retroesophageal left duct from diverticulum of Kommerell (rare) (see Fig. 42.5 )
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Left aortic arch with aberrant right subclavian artery (rare) and right-sided arterial duct (see Fig. 42.6 )
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Left aortic arch with retroesophageal right descending aorta, aberrant right subclavian artery, and right-sided duct (rare) (see Fig. 42.7 )
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Right aortic arch with aberrant left brachiocephalic artery and left-sided duct (very rare)
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Cervical aortic arch with aberrant subclavian artery and ipsilateral duct (see Fig. 42.8 )
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Vascular sling/compression
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Pulmonary artery sling (see Fig. 42.9 )
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Absent pulmonary valve syndrome
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Airway compression secondary to dilated and malposed aorta
Acquired Airway Compression
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Postoperative airway compression
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Compression by left atrium
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Aortic aneurysm
Vascular Rings
Double Aortic Arch
Double aortic arch (DAA) is the most common cause of tracheoesophageal compression, with an incidence of 46% to 76% in reports of vascular rings. Here, persistence of segment A (see Fig. 42.1B ) will result in a DAA ( Fig. 42.3 ), completely encircling the trachea and esophagus, sometimes leading to severe obstruction. Each aortic arch gives rise to respective common carotid and subclavian arteries. The arterial duct and the descending aorta are frequently left sided. The right (posterior) arch is usually dominant, although the two arches can be of the same size. The left (anterior) arch is dominant in approximately 20% of cases. Occasionally, the right or left arch (or a segment) can be atretic. This is more common on the left side, and it is worth remembering that these atretic segments cannot be visualized by any current imaging modality. Hence, it is sometimes difficult to differentiate the following:
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Right arch with a mirror image branching from a DAA with atresia of the segment beyond the LSCA (segment H, see Fig. 42.1B )
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Right arch with an aberrant LSCA from a DAA when the atretic segment is between the LCCA and LSCA (segments F and G, see Fig. 42.1B ).
DAA is commonly an isolated anomaly but can be seen occasionally in patients with tetralogy of Fallot, transposition of the great arteries, cervical arch, common arterial trunk, and coarctation of the aorta.
Right Aortic Arch with Aberrant Left Subclavian Artery
Right aortic arch with aberrant LSCA is the next most common cause of vascular ring (30% to 40%) and is a result of the absence of the fourth arch on the left side (segments F and G, see Fig. 42.1B ) with persistence of segments A and H (see Fig. 42.1B ). The aberrant LSCA has a retroesophageal course and forms an incomplete vascular ring if the arterial duct is right sided. However, in the presence of a left-sided arterial duct connecting the origin of the aberrant subclavian artery to the left pulmonary artery (LPA), the vascular ring becomes complete ( Fig. 42.4 ). This is usually loose, but it is tight when coming from a diverticulum of Kommerell, which is an outpouching from the distal remnant of the left aortic arch (see Fig. 42.4A ). The presence of the diverticulum of Kommerell is indicative of the existence of an arterial ligament (a DAA with atretic segment between the LCCA and LSCA). It is also worth remembering that the diverticulum of Kommerell can independently cause tracheoesophageal compression; hence, the symptoms might persist in some patients, despite the surgical division of the left-sided ligamentum.
The right aortic arch with aberrant LSCA and the right-sided arterial duct can occur in patients with tetralogy of Fallot, with or without pulmonary atresia or a common arterial trunk.
Right Aortic Arch with Mirror Image Branching
It is worth noting that a right-sided aortic arch with mirror image branching, caused by atresia of segment H (see Fig. 42.1B ), is seen in 2% to 3% of the population. The ductus arteriosus is usually left sided, arising from the LSCA. A right-sided arch on its own does not produce a vascular ring, although it may do so in association with other vascular anomalies. Extremely rarely, a duct may originate from a diverticulum of Kommerell and pass retroesophageally to join the LPA leading to a tight ring obstructing the left main bronchus ( Fig. 42.5 ).
Left Aortic Arch With Aberrant Right Subclavian Artery
A left aortic arch with aberrant RSCA is found in 0.5% of the normal population and is usually an incidental finding. Usually there is a left duct and no ring. There is persistence of segment A with atresia of segments B and C (see Fig. 42.1B and Fig. 42.6 ). It is also found commonly in association with tetralogy of Fallot (see Chapter 47 ). The aberrant RSCA usually takes a retroesophageal course and may cause symptomatic airway compression at the level of the arch and the RSCA (anteroposterior compression). Very rarely it may pass between the esophagus and trachea to cause dysphagia.
In the presence of a right-sided arterial duct from the RSCA, a complete but loose vascular ring is formed (see Fig. 42.6 ).
Left Aortic Arch with Retroesophageal Right Descending Aorta
This is an extremely rare anomaly in which the ascending aorta and the descending aorta are on the opposite sides of the spine with the aortic arch looping posterior to the esophagus. With a right duct there can be posterior indentation of the esophagus, but it is usually insufficient to cause symptoms ( Fig. 42.7A ). However, in the presence of an aberrant right subclavian and right duct from a diverticulum of Kommerell, there can be a complete ring (see Fig. 42.7B ).
Aberrant Left Brachiocephalic (Innominate) Artery
A right aortic arch with an aberrant left brachiocephalic artery (retroesophageal) and left duct can cause a loose vascular ring. Symptoms are variable depending on the extent of compression.
Cervical Arch
Very rarely a third arch component assumes the role of the definitive arch and presents as an abnormal pulsating feature in the neck, the so-called cervical arch. A right-sided cervical arch is more common than a left-sided arch. The descending aorta has a retroesophageal course, contralateral or ipsilateral, and commonly there is an aberrant subclavian artery. Where the arterial duct arises from the descending aorta contralateral to the side of the arch and with an aberrant subclavian artery, a vascular ring is formed ( Fig. 42.8 ). Even without the presence of a complete ring there may be tracheal compression secondary to overcrowding of vascular structures in the upper mediastinum. It is not uncommon to find associated arch tortuosity or even obstruction (coarctation) in the setting of the cervical arch. A double arch can sometimes be in a cervical position.
