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Aortic Arch, Vascular Rings and Slings

Terms in this set (90)

Aortic Arch Anomalies
Paul M. Weinberg MD
Congenital abnormalities of the aortic arch have been known at least since the anatomic reports of anomalous right subclavian artery by Hunauld in 1735 (1), double aortic arch by Hommel in 1737 (2), right aortic arch by Fioratti and Aglietti in 1763 (3), and interrupted aortic arch by Steidele in 1788 (4). Although the clinicopathologic correlation of swallowing difficulty with anomalous right subclavian artery was presented to the Medical Society of London by Bayford (5) in 1787, it was not until the 1930s and the use of barium esophagography that some arch anomalies were diagnosed during life. Since that time clinical interest has generally paralleled surgical capability. The first division of a vascular ring was performed by Gross in 1945 (6), and the first successful repair of interrupted aortic arch was accomplished by Merrill et al. in 1957 (7). In the current era with the advent of minimally invasive surgery (8,9) and more recently robotically assisted surgery (10), precise definition of aortic arch anatomy, preferably by noninvasive means, is essential.
Anatomical Classification [Print Section]
Aortic arch anomalies can be thought of as falling into one or a combination of the following anatomic categories: Abnormalities of branching, abnormalities of arch position including right aortic arch and cervical aortic arch, supernumerary arches including double aortic arch and persistent fifth aortic arch, interrupted aortic arch, and anomalous origin of a pulmonary artery branch from the ascending aorta or from the contralateral pulmonary artery branch.
Left and Right Arch Definition [Print Section]
Left and right aortic arch refer to which bronchus is crossed by the arch, not to which side of the midline the aortic root ascends. This is particularly important to remember when looking at projection images from angiography where it may be difficult to make the determination directly without significant cranial angulation. Practically, the sidedness of the aortic arch is usually determined indirectly with echocardiography or angiography by the branching pattern of the brachiocephalic vessels. As a rule, the first arch vessel contains the carotid artery opposite the side of the arch. However, caution must be exercised in using this indirect method, particularly when surgical decisions, such as the approach to repair of esophageal atresia, hinge on this determination. The very rare cases of retroesophageal or isolated innominate artery are exceptions to this rule. But by far the more common source of error in the use of this rule is the difficulty in deciding which of two carotid arteries is the first. A more reliable rule but one that may be difficult to apply with ultrasound imaging is that retroesophageal vessels or isolated vessels, i.e., arising only from a ductus or ligamentum (without connection to the aorta), are always opposite the side of the aortic arch. Magnetic resonance imaging (MRI) or computed tomography (CT) show the relationship of the arch to the trachea and bronchi directly, thus eliminating ambiguity when atypical branching patterns are encountered.
Embryology [Print Section]
The specific anomalies can better be understood through an appreciation of their embryologic origins. Development of the aortic arch system can best be described as a sequential appearance and persistence or dissolution of six paired vessels connecting the truncoaortic sac of the embryonic heart tube with the paired dorsal aortae, which fuse to form the definitive descending aorta. Each arch corresponds to a branchial pouch derived from embryonic foregut. Although the mechanism for determining persistence or dissolution of aortic arch components is not completely known, migration of neural crest cells into the pharyngeal arches (11) may play a significant role. In addition, the association of various arch anomalies such as right aortic arch, cervical aortic arch, aberrant and isolated subclavian artery, and certain vascular rings with microdeletions of chromosome 22q11 (12) implies a genetic component to the derivation of at least some arch anomalies. The fact that neural crest cells are also involved in development of the conotruncus and that conotruncal anomalies also occur in chromosome 22q11-deleted patients provides a further etiologic link to aortic arch anomalies.
The normal left aortic arch as shown by Congdon (13) is derived from the aortic portion of the embryonic truncus arteriosus, the left branch of the truncoaortic sac, the left fourth arterial arch, the left dorsal aorta between the fourth and sixth embryonic arches, and the left dorsal aorta distal to the sixth arch. The three brachiocephalic branches of the arch are derived from the following: The innominate artery from the right branch of the truncoaortic sac with the right common carotid artery from right third embryonic arch and right subclavian from right fourth arch and (proximal) right dorsal aorta proximally and right seventh intersegmental artery distally; left carotid artery from left third aortic arch; and left subclavian artery from left seventh intersegmental artery. Whereas the appearance and loss of vessels as arches or portions of the brachiocephalic vasculature is sequential, Edwards (14) proposed the concept of a "hypothetical double aortic arch" which is, in essence, the potential contribution of nearly all embryonic arches to components of the definitive arch system. These diagrams are used extensively in the excellent monograph by Stewart, Kincaid, and Edwards (15). They are invaluable not only to demonstrate possible embryologic explanations for each arch anomaly but also to help the diagnostician determine possible and probable arch anomalies and their corresponding sequences of arch vessels. We have adopted a simplified schematic version of
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the Edwards diagrams, which is feasible for those who are less artistically inclined, to provide similar information (Fig. 36.1). This can easily be drawn at the bedside or in the patient chart to diagram almost any arch anomaly and will be used throughout this chapter to illustrate many of the abnormalities.
Diagnostic Methods [Print Section]
Beginning in the 1930s, barium esophagography was the primary method for diagnosing arch anomalies. In the 1960s and 1970s, angiography became the gold standard and remained so even in the face of echocardiography. However, in the last 10 to 15 years, MRI and CT, where available, have supplanted angiography as the gold standard for definitive diagnosis of arch anomalies. Both modalities have the advantages of large fields of view and simultaneous visualization of vessels and airways, and both are minimally invasive. Although CT usually has shorter scan times, that advantage is disappearing as MRI sequences become faster. MRI has the advantage of no ionizing radiation—still a significant problem with CT even with the reduced dosage strategies used in some centers. Furthermore, MRI has capabilities for physiologic measurements, which are particularly helpful in patients with associated intracardiac disease.
There is still a role for ultrasonography in the diagnosis of arch anomalies and, in particular, vascular rings. That is in the fetus where the fluid-filled trachea does not preclude visualization the way the air-filled trachea does after birth. Furthermore, the ductus arteriosus is virtually always patent, so that nearly all rings can be seen completely encircling the trachea with blood-filled vessels. Specific strategies for recognizing vascular rings in the fetus have been reported by several authors (16,17,18).
Clinical Classification [Print Section]
In addition to the anatomic categorization of aortic arch anomalies discussed above, one can subdivide arch anomalies according to clinical features as follows: Vascular rings; nonring vascular compression of the trachea, bronchi, or esophagus; noncompressive arch malformations; and ductal-dependent arch anomalies including interrupted aortic arches and isolated subclavian, carotid, or innominate arteries. In addition, genetic syndromes represent an important group of patients from the standpoint of diagnostic criteria and associated abnormalities.
Chromosome 22q11.2 Deletion Syndromes [Print Section]
Chromosome 22q11.2 microdeletions are seen in >80% of patients with DiGeorge, velocardiofacial, and conotruncal anomaly face syndromes. The combination has been referred to collectively with the acronym CATCH 22 (cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, and hypocalcemia together with microdeletion of chromosome 22) (19). Most of these patients have conotruncal anomalies: Either subaortic stenosis with posterior malalignment of the infundibular septum often associated with interrupted aortic arch, type B; truncus arteriosus communis; or tetralogy of Fallot, with or without pulmonary atresia. More than two thirds of these have aortic arch anomalies (20). What is more, nearly one fourth of patients with arch anomalies but without intracardiac defects have 22q11 deletion (21). Although a wide variety of arch anomalies has been noted in these patients, there is a predilection for anomalies involving absence of one or both embryonic fourth aortic arches, as seen most notably in abnormalities of the subclavian arteries: Aberrant, isolated, or cervical origin (20,22,23). When all three types of subclavian artery anomaly are included, >80% of patients with both conotruncal and arch anomalies involving the subclavian artery have 22q11 deletion compared with only 17% of patients with conotruncal anomaly and normal subclavians (23). Other fourth arch anomalies occurring in chromosome 22q11 deletion syndromes include type B interrupted aortic arch, cervical aortic arch with separate origins of internal and external carotid arteries from the arch (24), and possibly stenosis in the middle of the right aortic arch between right carotid and subclavian arteries along with a diverticulum of Kommerell (25).
Vascular Rings [Print Section]
A vascular ring is an aortic arch anomaly in which the trachea and esophagus are completely surrounded by vascular structures. The vascular structures need not be patent, e.g., a ligamentum arteriosum or atretic segment of aortic arch may complete a ring. The clinical picture typically includes stridor, though pneumonia, bronchitis, or cough may characterize the presentation. Infants may demonstrate a posture of hyperextension of the neck. Less commonly, patients exhibit reflex apnea associated with eating. A common history is that of a 1- to 3-month-old with "noisy breathing since birth" who develops more significant respiratory distress in
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association with an intercurrent upper respiratory infection. Less commonly and usually in toddlers or older children, the presentation will be swallowing difficulty or choking on food. These patients tend to have looser rings, but careful questioning of parents will sometimes reveal the presence of stridor in infancy, which was passed off as "recurrent bronchitis." Occasionally, in patients with associated intracardiac abnormalities, respiratory symptoms may mistakenly be attributed to the cardiac disease when, in fact, they are in part or completely due to the vascular ring. Older children and adults are occasionally followed for many years with a diagnosis of asthma only to have a vascular ring diagnosed and surgically treated with resolution of symptoms (26,27). However, respiratory symptoms may persist for months or years after surgical relief of the ring owing to the presence of tracheomalacia. Some asymptomatic patients will be discovered incidentally while imaging for another reason (28). The diagnosis may be suspected from the combination of history and plain chest film; however, if symptomatic, the patient should have definitive study.
When all elements of the ring are patent, visualization, especially by tomographic imaging, is straightforward. In cases where the ring is completed by an atretic segment of aorta or ligamentum arteriosum, those segments cannot be visualized with current imaging technologies. However, these rings are recognizable by the presence of one of three "d"s opposite the side of the aortic arch: diverticulum, dimple, or descending aorta (Table 36.1). A diverticulum is a large vessel arising from the descending aorta that gives rise to a smaller-caliber vessel with a sudden taper. A dimple is a tapered, blindly ending outpouching from the aorta. Descending aorta opposite the side of the aortic arch refers to the location of the descending aorta in the upper thorax. These three "d"s occur only when connected by a ligamentum arteriosum or an atretic segment of aortic arch.
Normal Left Aortic Arch and Variants [Print Section]
The normal left aortic arch crosses the left mainstem bronchus at the level of thoracic vertebra T5 and descends left of the midline to the diaphragm and beyond in cases of visceral situs solitus. The normal branching pattern has the right innominate artery first. which, in turn, branches into the right common carotid and right subclavian arteries, the left carotid artery second, and the left subclavian artery third. Typically, the ductus arteriosus or the ligamentum arteriosum joins the aorta distal to the takeoff of the left subclavian artery but can insert more proximally, as in some cases of tetralogy of Fallot.
There are two frequent variants of the left aortic arch. One is common brachiocephalic trunk, in which the right innominate and left carotid arteries arise from a single origin. This is present in 10% of otherwise normal left arches (29) and usually is of no consequence, although some have suggested that innominate artery compression of the trachea (discussed below) is more frequent when common brachiocephalic trunk is present. The other variant is separate origin of the left vertebral artery from the aortic arch proximal to the takeoff of the left subclavian artery rather than from the subclavian artery (Fig. 36.2A).
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This too is seen in 10% of normal left arches (29) and is important only in the fact that it should not be confused angiographically or echocardiographically with anomalous right subclavian artery in which there are also four brachiocephalic vessels (see below). The distinguishing feature here is the normal appearance of the first arch vessel (right innominate artery), being larger than the second (left carotid), and the third (left vertebral) being smaller than the fourth (left subclavian). Again, no functional significance attends this common variant.
Embryology [Print Section]
Using the totipotential aortic arch diagram (Fig. 36.2B), one envisions the normal left arch resulting from dissolution of the right sixth aortic arch (ductus) and the right dorsal aorta distal to the origin of the seventh intersegmental artery (distal subclavian artery precursor). Thus the right fourth arch, rather than remaining an arch (connecting truncoaortic sac to descending aorta), becomes the proximal right subclavian artery as it arises from the innominate artery. The left fourth arch becomes the definitive aortic arch.
Abnormal Left Aortic Arch [Print Section]
Left Aortic Arch with Retroesophageal Right Subclavian Artery [Print Section]
This anomaly (also called anomalous or aberrant right subclavian artery) was first described anatomically by Hunauld in 1735. Bayford (5) linked the postmortem discovery of such a case with the history of swallowing difficulty during life and coined the term "dysphagia lusoria" (from the Latin, lusus naturae, trick of nature).
The branching pattern shows the first branch to be the right carotid artery, the second the left carotid, third the left subclavian, and fourth a retroesophageal right subclavian artery arising from the posteromedial aspect of the distal aortic arch (Fig. 36.3A). This is the most common arch anomaly, occurring in 0.5% of the general population, demonstrated in a large adult autopsy series (30). The incidence in Down syndrome patients with congenital heart disease is very high at 38% (31). Most cases of left aortic arch with retroesophageal right subclavian artery are asymptomatic, with the diagnosis made while imaging for another condition or at autopsy. Associated anomalies may include tetralogy of Fallot, various types of isolated ventricular septal defect (VSD), and a smattering of other intracardiac defects.
Embryology
This can be envisioned as a disappearance of the right fourth aortic arch (Fig. 36.3F). The distal right dorsal aorta (rather than the right fourth arch) becomes the proximal right subclavian artery forming its retroesophageal portion. The right sixth arch (ductus) also involutes.
Diagnosis and Management
Since there is no innominate artery, the first and second branches, the right and left carotid arteries, respectively, tend to be similar in size as are the last two branches, the left and right subclavian arteries. Barium esophagography is usually specific for the diagnosis with a fixed filling defect usually slanting upward to the right and best appreciated with fluoroscopy. The defect is relatively small (Fig. 36.3E) compared with that seen in other anomalies where an aortic arch, or
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diverticulum, impinges on the esophagus (compare Fig. 36.11F). With angiography, the diagnosis may sometimes be missed in the anteroposterior projection since the right subclavian may be superimposed on the right carotid artery in the usual position. However, careful single-frame analysis will demonstrate the earlier filling of the right carotid on an aortic root injection or the earlier filling of the right subclavian on a descending aortic injection. This arch anomaly is usually recognized with echocardiography by the branching pattern discussed above, namely, a nonbifurcating first branch that ascends toward the right, followed by two successive left-sided vessels (left carotid and left subclavian arteries) followed by a fourth branch that
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heads toward the right but may disappear behind the trachea. The retroesophageal course of the subclavian artery is shown by MRI on transverse (axial) cuts, and the largest expanse from aortic origin to the thoracic apex is usually seen on coronal sections.
Left Aortic Arch with Retroesophageal Diverticulum of Kommerell [Print Section]
This very rare arch anomaly was actually the first vascular ring to be diagnosed in life with barium esophagography by Kommerell (32) whose name is associated with this diverticulum. Although the name is usually used in reference to the much more common mirror image of this anomaly, viz., a diverticulum associated with a right aortic arch (discussed below). The branching pattern in left arch with retro-esophageal diverticulum is identical to that of the more common left arch with retroesophageal right subclavian artery discussed above, which is not a vascular ring. The difference is in the caliber of the proximal subclavian artery (Fig. 36.4A, B). The significance of this is that the abrupt change of vessel size always indicates the presence of a ligamentum arteriosum, which completes a vascular ring.
Embryology
The embryology of this anomaly, also similar to left arch with retroesophageal subclavian artery, can be thought of as a disappearance of the right fourth aortic arch but with the distal left dorsal aorta forming the definitive distal aortic arch and passing retroesophageally to a descending aorta beginning to the right of the vertebral column (Fig. 36.5D). Thus the right seventh intersegmental artery arises from the right-sided descending aorta. There is also persistence of the right sixth (ductal) arch connecting the right pulmonary artery portion of the truncoaortic sac with the distal right dorsal aorta similar to the also rare left arch diverticulum of Kommerell (above).
Diagnosis and Management
This diagnosis can be suspected if a patient who presents with symptoms suggestive of a vascular ring has findings of a left
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aortic arch without evidence of a right aortic arch. Plain chest roentgenogram can show the left-sided arch and the right-sided upper descending aorta, particularly in adults. The addition of barium esophagography can demonstrate the large posterior indentation from the retroesophageal aorta; however, the course of this vessel, upward to the left, is indistinguishable from the much more frequently occurring right aortic arch with retroesophageal diverticulum (see below). In both cases the upper descending aorta is right sided. Although the aortic knob on chest roentgenogram would be left sided, this is not always evident, especially in infants with a prominent thymus. Angiography will show the course of the aorta from left arch to retroesophageal segment to right upper descending. The subclavian artery can be seen arising from the descending aorta as it turns from its transverse to more nearly vertical course. This pattern can also be demonstrated by MRI with the addition of direct imaging of the aortic position relative to the trachea. Although most vascular rings can be divided through a left thoracotomy, this type and the rare diverticulum of Kommerell noted above are usually approached by a right thoracotomy (33), so that the ligamentum can be reached. A midline approach may also be used.
Left Aortic Arch with Isolated Subclavian Artery [Print Section]
Another rare anomaly, isolated subclavian artery, means that the subclavian artery arises only from the ductus arteriosus. While the ductus is patent, the subclavian and vertebral arteries are supplied from the pulmonary artery. When the ductus closes, the subclavian is supplied by retrograde flow from the vertebral artery via the circle of Willis.
Embryology
This occurs with dissolution of the right fourth arch and right dorsal aorta but persistence of the right sixth arch.
Diagnosis and Management
When this occurs in the absence of other anomalies, it may go unrecognized or may cause vertebrobasilar insufficiency with so-called congenital subclavian steal. In many cases there may be no symptoms or simply absence of the right arm pulse. This may be recognized with angiography by delayed filling of the subclavian artery after aortic root injection. With phase-encoded velocity mapping, retrograde flow in the vertebral artery can be detected on MRI. Symptomatic patients are treated by implantation of the subclavian artery into the aorta.
Left Aortic Arch with Cervical Origin of the Right Subclavian Artery [Print Section]
This rare anomaly was first reported by Kutsche and Van Mierop (34) in association with type B interrupted aortic arch. It was subsequently found in patients with tetralogy of Fallot, with or without pulmonary atresia, and has been seen only in patients with 22q11 deletion (22). This is an abnormality whose clinical significance appears to be that it is a marker for CATCH 22. Normally the right innominate artery bifurcates into a common carotid and subclavian artery near its origin from the aorta (see Fig. 36.2B). In this anomaly, the innominate trifurcates in the neck, giving rise to external and internal carotids and the subclavian artery, which then travels caudally back to the thorax before heading out to the arm (Fig. 36.6).
Embryology
The presumptive embryology has been elegantly described by Kutsche and Van Mierop (34). This together with the observation of Rauch, et al. (22) that abnormalities of subclavian artery origin are frequently associated with 22q11 deletion sheds light on an important pathway in the pathogenesis of arch anomalies in CATCH 22 patients. There appears to be a predilection for unilateral or bilateral absence or atresia of the embryonic fourth arch. When this occurs on the side opposite the definitive arch, there are three main variations in the fate of the subclavian artery: (a) origin from the descending aorta, i.e., from the dorsal aorta distal to the seventh intersegmental artery—retro-esophageal subclavian artery or circumflex aortic arch as described above; (b) origin from the sixth arch—isolated subclavian artery, also described above; and (c) origin from the third arch, which, being more cephalad than the fourth, gives origin to the subclavian artery in the neck rather than in the thorax.
When the fourth arch is absent or atretic ipsilateral to the definitive aortic arch, there are also three possibilities, which will be elaborated on below: (a) interrupted aortic arch, in which the sixth arch replaces the fourth; (b) persistent fifth aortic arch with atresia of the distal fourth; and (c) cervical aortic arch, in which the third arch replaces the fourth, analogous to cervical origin of the subclavian artery on the side opposite the arch. Of note is the fact that all of these have been seen in association with 22q11 deletion and collectively are more common than cases with normal origin of the subclavian arteries and well-developed fourth arches (20,23).
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Right Aortic Arch [Print Section]
Right aortic arches have in common (by definition) a single aortic arch that crosses over the right mainstem bronchus, passing to the right of the trachea. There are four major types of right arch: (a) with mirror image branching, (b) with retroesophageal left subclavian artery, (c) with retro-esophageal diverticulum, and (d) with left descending aorta. There are also several infrequently occurring variations.
The incidence of right aortic arch among patients with tetralogy of Fallot has been reported to be anywhere from 13% to 34% (35); however, studies vary as to the source of the material (chest roentgenogram, angiography, surgery, or postmortem examination) and frequently do not distinguish between specific types of right arch. The incidence in truncus arteriosus is generally higher than in tetralogy. An overall incidence of 8% in patients with D-transposition of the great arteries, compared with 16% in those with transposition VSD and pulmonary stenosis, has been reported (36).
Right Aortic Arch with Mirror-Image Branching [Print Section]
Mirror-image right arch has the first branch as a left innominate artery, which, in turn, divides into left carotid and left subclavian arteries; the second as the right carotid; and the third a right subclavian (Fig. 36.7A, B). This is the left-right mirror of a normal left aortic arch. However, frequently that is the end of the symmetry, since the ductus arteriosus (or ligamentum arteriosum) is usually the left-sided one, arising from the base of the innominate artery rather than from the aortic arch. Therefore, typical mirror-image right aortic arch with left ductus or ligamentum does not form a vascular ring. This arch anomaly is almost always associated with congenital intracardiac disease. The most common association is with tetralogy of Fallot (48% in a series of 74 postmortem cases) (37), but truncus arteriosus communis, other conotruncal anomalies including transposition of the great arteries, double-outlet right ventricle, right ventricular aorta
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with pulmonary atresia, and anatomically corrected malposition were also seen. In addition, lesions not usually considered being conotruncal anomalies such as pulmonary atresia with intact ventricular septum, conoventricular/perimembranous VSD with anomalous muscle bundle of the right ventricle, and isolated VSD are occasionally found to have mirror-image right arch.
A rare variation of mirror-image right aortic arch has a left ductus or ligamentum arising from a retroesophageal dimple from the right-sided descending aorta. This does form a vascular ring (Fig. 36.8). This is different from right arch with diverticulum of Kommerell in that no arch vessel arises from the dimple. Unlike other patients with mirror-image right aortic arch, the few reported cases with retroesophageal ductus dimple appear not to have associated congenital heart disease (38).
Embryology
The presumptive pattern of mirror-image right arch development includes dissolution of the left dorsal aorta distal to the
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origin of the seventh intersegmental artery (distal subclavian artery precursor) so that the left fourth arch becomes the proximal subclavian artery rather than remaining as an aortic arch (Fig. 36.7C). Typically, the right sixth (ductal) arch involutes while the left sixth persists. However, with disappearance of the left dorsal aorta distal to the left seventh intersegmental artery, the sixth arch usually connects to the proximal or subclavian artery side of the disruption. Thus, in the definitive arch the left ductus arises from the underside of the left innominate artery and passes to the left pulmonary artery, appearing as a congenital modified left Blalock-Thomas-Taussig shunt. Alternatively, the left sixth arch will disappear and the right persist, giving a true mirror image of normal, that is, a ductus connecting the underside of the right-sided arch with the right pulmonary artery. Other cases, particularly when associated with tetralogy of Fallot, may have dissolution of both ductus. Finally, in those with retroesophageal ductus dimple, the left sixth arch connects the left pulmonary artery with the distal left dorsal aorta (Fig. 36.8F).
Diagnosis and Management
Since this type of right arch usually produces no retro-esophageal compression or vascular ring, there are, with rare exception, no symptoms produced by the arch itself. Therefore, the diagnosis is usually made during imaging of the associated congenital intracardiac disease. The distinctive branching pattern can be used for echocardiographic and angiographic diagnosis, whereas the appearance of a right-sided indentation of trachea and esophagus on plain radiograph and barium esophagography, respectively, but without posterior impression on the esophagram, permits the diagnosis to be made with those modalities. The presence of a left innominate artery in a patient with symptoms suggestive of a vascular ring and in the absence of cyanotic congenital heart disease should suggest the differential diagnosis of the rare right arch, retroesophageal ductus or the more common right arch, left descending aorta or double aortic arch with atretic left arch distal to the subclavian artery (discussed below), which is differentiated by presence of a left upper descending aorta.
No treatment of right aortic arch per se is required; however, it may be helpful for surgeons to know the sidedness of the aortic arch in certain circumstances. For systemic-to-pulmonary shunts, the classical Blalock-Thomas-Taussig (subclavian artery to pulmonary artery, direct end-to-side) anastomosis or the modified form (polytetrafluoroethylene [Gore-Tex] tube graft interposition side-to-side anastomosis of subclavian artery to pulmonary artery) are best carried out using the side with an innominate artery. With the classic form, the more nearly horizontal takeoff of the subclavian artery makes kinking of the vessel less likely when the cut end is brought down to the level of the pulmonary artery than with the subclavian artery arising directly from the arch. Even with Gore-Tex tube graft interposition, the innominate is a more favorable site of origin since the overall diameter of the innominate is greater, making the proximal anastomosis easier. Furthermore, the angle of takeoff is less acute, making kinking of the vessel of origin less likely even if there is some downward traction after completion of the anastomosis. Another situation in which knowledge of the side of the aortic arch may be useful is in the repair of esophageal atresia and tracheoesophageal fistula where it may be desirable to avoid having the arch obscure the view of the fistula.
Right Aortic Arch with Retroesophageal Diverticulum of Kommerell [Print Section]
Right arch with diverticulum of Kommerell is the second most common vascular ring after double aortic arch. It is far more common than its mirror image described above. It has as its first branch the left carotid artery, second the right carotid artery, third the right subclavian artery, and finally, a retro-esophageal vessel from which the left subclavian artery arises and the left ductus arteriosus or ligamentum arteriosum connects (Fig. 36.9). This combination of vessels produces a
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vascular ring. The true incidence of this lesion is more difficult to obtain than that of mirror-image right arch where virtually all patients have associated intracardiac disease. However, of 26 consecutive patients undergoing surgical division of vascular rings at our institution, five (19%) had right arch, retro-esophageal diverticulum, and most of them had no other heart defect. What is more, many people with this arch anomaly are asymptomatic and therefore go unrecognized except for incidental discovery.
If the ductus arteriosus is patent, it is easy to understand how one might visualize the complete ring formed by the aortic arch on the right, retroesophageal vessel supplying the left subclavian posteriorly, the ductus on the left and the pulmonary artery anteriorly. However, if the ductus is closed, it is not intuitive that one could distinguish this from the more benign right arch with retroesophageal subclavian artery (nonring) discussed below. The difference is the diverticulum of Kommerell, which is a much larger vessel than the subclavian artery itself. Typically, the origin of the diverticulum is equal in diameter to the descending aorta and tapers to the subclavian artery caliber at the site of juncture with the left ligamentum.
Embryology
Disappearance of the left fourth embryonic arch with persistence of the left sixth (ductal) arch between the truncoaortic sac (pulmonary artery precursor) and left dorsal aorta accounts for the findings in this arch anomaly (Fig. 36.9D). Note that the left dorsal aorta is not merely the proximal left subclavian artery but is also the continuation of the left sixth aortic arch leading to the fused dorsal aortae. Since the normal fetal ductus carries nearly the entire output of the right ventricle, the left dorsal aorta would also carry that amount and would become significantly larger than the subclavian artery. This size discrepancy persists after ductal closure, giving the diverticulum its characteristic appearance.
Diagnosis and Management
The presentation in symptomatic patients is usually that of a vascular ring. With that history, the appearance of a right aortic arch on a plain chest roentgenogram should raise the question of this anomaly and prompt further, more specific evaluation. Barium esophagram reveals a large posterior indentation on the esophagus similar to that seen in Figure 36.11E, in contrast to the smaller defect seen with simple retroesophageal subclavian artery (Fig. 36.3B). However, rare vascular rings such as left aortic arch with right descending aorta and right ligamentum can give similar findings on barium study, and since the surgical approach is different, this form of imaging should not be considered definitive. Although the ligamentum arteriosum is not visualized with any of the current imaging modalities, its presence is guaranteed by the characteristic appearance of the tapered diverticulum. Echocardiography will show the left carotid artery arising alone as the first arch vessel, but definitive diagnosis requires that the diverticulum be followed out to the point at which the caliber changes to that of the smaller subclavian artery. This is usually not possible since the trachea itself and nearby lung may thwart attempts to see this area. Angiography demonstrates the characteristic branching pattern, but more important, shows the abrupt change in caliber from diverticulum to subclavian artery. As mentioned previously in the section on left aortic arch with retroesophageal right subclavian artery, angiography in the straight anteroposterior (AP) view may produce superimposition of the posterior subclavian artery on the more anterior left carotid, giving the appearance of a left innominate artery as in mirror-image right aortic arch and therefore not a ring. However, careful single-frame viewing of cineangiography will confirm the separate origins. Contrast injection in the more distal portion of the arch will better delineate the plump aortic diverticulum giving rise to the noticeably smaller subclavian artery. Angiography, although definitive, showing both the characteristic branching pattern and the typical appearance of the aortic diverticulum requires arterial catheterization, less desirable in the young infant. Magnetic resonance imaging is ideal for making this diagnosis, being noninvasive and having the ability to display both vascular and airway structures. Axial or transverse imaging demonstrates the aortic arch to the right of the trachea and the diverticulum posterior to it. Coronal imaging shows the V-shaped juncture of the aortic diverticulum and the more right-sided descending aorta. However, computer-generated shaded-surface displays (three-dimensional representations) permit viewing of the entire aortic arch at once and in relationship to trachea and pulmonary artery (Fig. 36.9A-C), giving the surgeon a clear anatomic image with which to proceed.
Most people with this arch anomaly are asymptomatic. Treatment is surgical division of the ductus or ligamentum in those patients who are symptomatic. This is usually performed through a left thoracotomy, although a median sternotomy approach is preferred by some. Still others advocate not only division of the ligamentum but resection of the diverticulum and transfer of the left subclavian artery to the left carotid artery because of the recurrence of symptoms in some patients owing to compression from an aneurysmal diverticulum and traction by the subclavian artery (39).
In those patients undergoing surgery for another lesion such as an intracardiac abnormality or repair of tracheo-esophageal fistula, even an asymptomatic ligamentum should be divided. With esophageal atresia, a symptomatic ring may be avoided when repairing the esophagus outside the ring.
Right Aortic Arch with Retroesophageal Left Subclavian Artery [Print Section]
Right aortic arch with retroesophageal (also called anomalous or aberrant) left subclavian artery consists of an arch passing to the right of the trachea with the following sequence of brachiocephalic arteries: Left carotid, right carotid, right subclavian, and retroesophageal left subclavian (Fig. 36.10A, B). This differs from the previous arch in that the proximal left subclavian artery is not significantly larger in caliber than its more distal portion (i.e., no aortic diverticulum). Therefore, there is no left-sided ductus arteriosus or ligamentum arteriosum and thus no vascular ring. Many of these patients have associated conotruncal anomalies. As has been noted previously, aberrant subclavian artery has a higher incidence of 22q11 deletion than does mirror-image right aortic arch (20).
Embryology
This is similar to the right arch with retroesophageal diverticulum with involution of the left fourth aortic arch but with loss of the left sixth (ductal) arch (Fig. 36.10C). In this way, the left dorsal aorta becomes only the proximal left subclavian artery and not the beginning of the descending aorta. A right sixth arch, if present, connects right pulmonary artery with right dorsal aorta, which is part of the definitive right arch.
Diagnosis and Management
The diagnosis may be suspected from barium esophagography with a relatively small posterior indentation on the esophagus passing upward to the left. Since there is no vascular ring, the trachea is unaffected except for the slight leftward deviation seen with virtually all right aortic arches. As noted above, echocardiography may be expected to identify the first branch of the aorta as a left carotid artery (since it does not bifurcate proximally as an innominate artery does and is similar in caliber to the second branch—right carotid artery), but appreciation of the size of the retroesophageal vessel itself may be difficult. Both magnetic resonance imaging and angiography can demonstrate the size of the left subclavian artery, which distinguishes this lesion from right aortic arch with retroesophageal diverticulum. Since there is no vascular ring, there is usually no need for treatment other than that of associated anomalies.
Right Aortic Arch with Left Descending Aorta and Left Ductus Arteriosus or Ligamentum Arteriosum [Print Section]
Right arch, left descending aorta, also known as right aortic arch with retroesophageal segment or circumflex right aortic
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arch, is similar in presentation to right arch with retro-esophageal diverticulum (above), but it is less common. Unlike cases with retroesophageal diverticulum in which the aorta, after passing over the right mainstem bronchus, descends for some distance on the right, then gradually crosses to the left before reaching the level of the diaphragm, right arch left descending (aorta) has the aortic arch itself cross the midline to the left at the level of the T4 or T5 vertebral body, at which point it gives rise to the left ductus arteriosus or ligamentum arteriosum (Fig. 36.11). The first arch vessel may be the left innominate, followed by right carotid and right subclavian, or the left carotid artery alone, followed by the right carotid, right subclavian, and finally the left subclavian (Fig. 36.12). However, it is the aortic arch that is retroesophageal, not the subclavian artery or an aortic diverticulum.
With a projection image such as angiography, it may not be clear whether the aorta passes anterior to the trachea as it courses from right ascending to left descending, as is seen with a normal left aortic arch, or posterior to the trachea, i.e., a right aortic arch with left descending. A clue to which is the case (without attempting steep cranial angulation (usually more confusing than helpful because of overlapping shoulder, head, and liver) is the order of brachiocephalic artery branching. In the case of right aortic arch with left descending aorta, the first vessel contains the left carotid artery, whereas in normal left arches, a vessel containing a right carotid is first. Magnetic resonance imaging can avoid some of the pitfalls seen with projection images and can delineate the entire aorta, not only in its normal rightward ascending and leftward descending segments, but definitively in its relationship to the trachea (Fig. 36.11 A, B).
Division of the vascular ring is indicated when patients are symptomatic, although these are typically loose rings. However, an adult with dysphagia may require more than simple division of the ligamentum. Actual division of the aortic arch with mobilization of the retroesophageal portion and reanastomosis of ascending and descending aorta using a tube graft may be necessary to relieve the esophageal compression (41,42).
Right Aortic Arch with Retroesophageal Innominate Artery [Print Section]
Right aortic arch with retroesophageal (or aberrant) innominate artery is another rare abnormality of the aortic arch system. Contrary to the general rule that the first arch vessel contains a carotid artery contralateral to the aortic arch, in these cases the sequence of brachiocephalic vessels is right carotid, right subclavian, retroesophageal left innominate artery (Fig. 36.13A). The ductus arteriosus or ligamentum arteriosum completes a vascular ring as it connects the left pulmonary artery with the base of the so-called innominate artery.
Embryology
The apparent site of arch dissolution is in the left branch of the truncoaortic sac (Fig. 36.13B). Thus the arch is formed by the right branch leading to the right fourth arch, which, in turn, connects to the right dorsal aorta. The left dorsal aorta supplies the left seventh intersegmental artery (distal left subclavian) and the left third arch (common carotid artery). It is not clear whether any remnant of the left fourth arch persists, although it may form the proximal left carotid artery.
Diagnosis and Management
With so few cases in the literature (43), it is difficult to draw conclusions about presentation and management. Tracheal compression seems to be the rule, although the degree of symptomatology varies considerably. The important anatomic clues to the diagnosis by any imaging modality are the presence of a single carotid artery arising from the proximal aorta. The other anomalies with that finding are also rare: Interrupted aortic arch with interruption between the two carotid arteries and isolated left carotid or innominate artery (see below). The differentiating feature is the presence of a normal-sized (right) aortic arch (missing in arch interruption) and the distal origin of the carotid artery from that arch (not present with isolated carotid or innominate). If symptomatic from the vascular ring, division of the ductus or ligamentum is in order. Conceivably in the adult, detachment of the innominate artery
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from the distal arch and reimplantation in the ascending aorta might be necessary based on similar arch anomalies mentioned above in which the retroesophageal vessel continued to cause dysphagia even after relief of the ring by division of the ligamentum.
Right Aortic Arch with Isolation of Contralateral Arch Vessel [Print Section]
Isolation of brachiocephalic vessels is relatively uncommon. The term isolation means that the particular vessel arises exclusively from the pulmonary artery via the ductus arteriosus (or ligamentum) but without connection to the aorta. Three different forms have been noted: Isolation of the left subclavian artery (Fig. 36.14), isolation of the left carotid, and isolation of the left innominate artery. Isolated left subclavian is by far the most common of the three. Leutmer and Miller (44) reviewed the literature to 1990 describing 39 cases demonstrated by angiography or at postmortem examination. Congenital heart disease was found in more than half the cases with two thirds of those having tetralogy of Fallot. There are sporadic reports of isolated left innominate artery (45). A forme fruste is shown in Figure 36.15 with a small innominate artery and larger subclavian and carotid, suggesting that during fetal life they had been fed by a left ductus that had since closed.
Embryology
All cases of isolated arch vessels derive from two ipsilateral breaks in the aortic arch system (Fig. 36.14B). In isolated subclavian artery, the distal left dorsal aorta involutes after cephalad migration of the left seventh intersegmental (subclavian) artery to the level where left sixth (ductal) arch normally joins the proximal dorsal aorta. This together with involution of the left fourth arch leaves the subclavian isolated from the aortic arch but connected to the pulmonary artery via the ductus. In similar fashion, one could imagine disappearance of the left fourth arch and the left branch of the aortic sac with the sixth arch connecting the pulmonary artery portion of the truncoaortic sac to the third arch (common carotid artery precursor). With disruption of the left fourth arch, the left seventh intersegmental artery remains connected to the descending aorta via the left dorsal aorta, producing a retroesophageal left subclavian artery. It is postulated that isolated innominate artery derives from dissolution of the left branch of the aortic sac and the distal left dorsal aorta with the left sixth (ductal) arch connecting the pulmonary portion of the truncoaortic sac and the proximal dorsal aorta, which, in turn, feeds the left seventh intersegmental (subclavian) artery and the left third arch via the fourth. The resulting confluence of carotid and subclavian arteries is analogous to an innominate artery. An alternative mechanism based on identification of a pulmonary-to-brachiocephalic artery connection proximal to or upstream from the ductus in chick embryos is explained by an abnormal partition of the truncoaortic sac (46).
Surgical management in children consists of repair of the accompanying heart disease and ligation of the ductus, if patent, to prevent pulmonary steal. Patients with central nervous system symptoms or claudication of the left arm may require surgical reimplantation of the subclavian artery into the carotid or aorta.
Cervical Aortic Arch [Print Section]
Cervical aortic arch is a rare anomaly in which the arch is found above the level of the clavicle (as high as the C2 vertebral body). There are two main subcategories of cervical arch: Those with anomalous subclavian artery and vascular ring, with either descending aorta contralateral to the arch (see Fig. 36.5) or retroesophageal diverticulum, and those with a virtual normal branching pattern. The first and larger group usually has a right aortic arch. This group is further subdivided into those with separate origins of the internal and external carotid arteries from the arch and those with a common carotid artery or a bicarotid trunk in which both common carotid arteries arise from a single vessel and the subclavian arteries both arise separately from the distal arch (49). Separate origin of the vertebral artery from the arch can be seen in each of the groups. Although most of the patients with contralateral descending aorta have an anatomic vascular ring from the aortic arch on the right, retroesophageal segment of aorta posteriorly, ligamentum arteriosum to the left, and pulmonary artery anteriorly, only about half are symptomatic from the ring. When a bicarotid trunk accompanies the contralateral descending aorta form of cervical arch, tracheal or esophageal compression between the "V" of the bicarotid trunk and the retroesophageal aorta may occur without a complete vascular ring.
The second group (with ipsilateral descending aorta—nonring) typically has a left aortic arch. Aortic arch obstruction owing to a long, tortuous, hypoplastic retroesophageal segment is an uncommon but well-documented association (50). More discrete coarctations have been reported in both the ring and nonring groups (51). For reasons that are not clear, stenosis or atresia of the origin of the left subclavian artery is sometimes seen in either group (52).
Embryology [Print Section]
It would appear that the embryologic explanations for the various subgroups mentioned above are different. The normal common carotid artery comes about from the dissolution of the segment of dorsal aorta between the third and fourth embryonic arches, the so-called ductus caroticus. Both internal and external carotid arteries arise from the third arch. If the ductus caroticus were to persist while the embryonic fourth arch involutes, the embryonic third arch would become the definitive arch with separate internal and external carotid arteries arising from it (as they had when the third arch was, in part, the common carotid artery) (53). The third arch, being one branchial pouch higher than the fourth arch, would be expected to be more cephalad after completion of arch development. This type of cervical arch (i.e., with separate internal and external carotid arteries arising directly from the arch) owing to persistent ductus caroticus and absent fourth arch has been described in chromosome 22q11 deletion as previously mentioned (54).
An alternative explanation for this subgroup and more plausible for the other groups that have normal common carotid arteries, is a failure of the normal descent of the aortic arch system from its cephalic location at 3 weeks to its normal intrathoracic location by 7 weeks' gestation (55). The cause of this failure of caudal migration is not known.
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Diagnosis and Management [Print Section]
Cervical arches may present as pulsatile masses in the supraclavicular fossa or in the neck. In infants, prior to the appearance of a mass, the presenting signs may be those of a vascular ring, namely, stridor, dyspnea, or repeated lower respiratory infections. In the adult, the most likely symptom from a vascular ring is dysphagia. In those patients with stenosis or atresia of the left subclavian artery and origin of the ipsilateral vertebral artery distal to the obstruction, a subclavian steal may exist with central nervous system symptomatology. In the presence of a pulsatile neck mass, a presumptive diagnosis can be made by notation of loss of femoral pulses during brief compression of the mass (52).
The diagnosis of cervical arch may be suspected on plain chest roentgenogram by the presence of a widened upper mediastinum and the absence of the aortic knob. Evidence of anterior deviation of the trachea is in favor of the diagnosis. In the past, angiography has been the standard diagnostic imaging tool, and in those cases with intracardiac anomalies, probably remains so. However, in those without congenital heart disease, the diagnosis of cervical aortic arch can by made by echocardiography. Treatment is necessary if the cervical arch is complicated by arch hypoplasia, symptomatic vascular ring, or rarely, aneurysm of the cervical arch itself (56). In these cases the surgical approach is dictated by the specific complicating feature. In some cases with cervical right aortic arch and a tortuous, hypoplastic retroesophageal segment, repair is accomplished by left-sided ascending-to-descending aorta anastomosis or tube graft interposition (57). Separate origin of external and internal carotid arteries from the arch warrants screening for 22q11 deletion.
Double Aortic Arch [Print Section]
Double aortic arch, as the name implies, is an anomaly in which both right and left aortic arches are present. Several variations on this basic theme occur: Both arches widely patent (Fig. 36.16A-D, G-K), hypoplasia of one arch (usually the left) (Fig. 36.16E, F), (occasionally the right) (Fig. 36.16L), and atresia of one arch, usually the left (Fig. 36.17). In addition, a ductus arteriosus or ligamentum may be present. Typically the right arch is the more superiorly located.
Although all double aortic arches technically form complete vascular rings around the trachea and esophagus, the branching pattern evident from various imaging modalities is determined by the patency of the various arch components and the side of the descending aorta. For example, whereas a double arch with both arches patent will show relatively symmetric origins of each of the four major brachiocephalic arteries from their respective arches (see Fig. 36.16K, L), double arch with atretic left arch distal to the origin of the left subclavian artery (see Fig. 36.17) will have a branching pattern similar to a mirror-image right aortic arch, that is, an apparent left innominate artery, followed by a right carotid and right subclavian, but with a left descending aorta. In fact, this pattern in conjunction with signs of tracheal compression may be indistinguishable (except at surgery) from the rare anomaly right aortic arch with left descending aorta, unless, as in Figure 36.17A, a distal left arch stump is present. Similarly, double arch with atretic left arch between left carotid and left subclavian can mimic right aortic arch with retroesophageal diverticulum of Kommerell. Atretic right arch is quite rare (58) but can simulate left arch variants. Of 17 patients at one institution undergoing division of the vascular ring, 11 had a left descending aorta, 6, a right (59). A review of 26 patients undergoing surgical division of vascular rings over an 8-year period at The Children's Hospital of Philadelphia showed 20 to have double aortic arches. Seventeen had both arches patent with the right arch larger in 16. The other three patients had an atretic left arch.
Double aortic arch is rarely associated with congenital heart disease, but when present, tetralogy of Fallot is most common (60), with transposition of the great arteries a distant second (60). Infrequent associated arch abnormalities including coarctation of the left (61) or both arches (62) and cervical left aortic arch (63) have been noted.
Embryology [Print Section]
Double aortic arch represents a persistence of both right and left embryonic fourth branchial arches joining the aortic portion of the truncoaortic sac to their respective dorsal aortae, both of which persist as well. Thus double aortic arch with both arches patent appears as persistence of the entire hypothetic double arch (Fig. 36.1) although usually with only one sixth (ductal) arch, whereas double arch with atretic left arch has patterns similar to either right arch with retroesophageal diverticulum (compare Fig. 36.17B with Fig. 36.9D) or right arch, left descending aorta (compare Fig. 36.17C with Fig. 36.11G). In keeping with the theme of absent or atretic fourth arches in 22q11 deletions, double arch with atretic left arch is more commonly associated with those syndromes than double arch with both widely patent.
Diagnosis and Management [Print Section]
The clinical manifestations of double aortic arches, as with the other vascular rings, are related to the tightness of the ring. With both arches widely patent, the rings are typically tight, and patients present with stridor in the first weeks of life, whereas with double arch and atretic left arch, the rings are usually looser with presentations at 3 to 6 months of age or later. Rarely, double aortic arches present in adulthood with swallowing or respiratory symptoms (64). The diagnosis of double arch with both arches patent can sometimes be made convincingly from the plain chest roentgenogram. The tracheal air column is indented by the more superior, right-sided arch and the more inferior left arch. In the lateral view, the right arch can be seen to indent the trachea posteriorly. These findings may be more obvious with barium esophagography. However confirmation by echocardiography, angiography, or magnetic resonance imaging is desirable because the two arches may be unequal in caliber, and it is important to identify the hypoplastic segment to divide it. In addition, a weblike coarctation of one arch may not be detectable by the surgeon from the external appearance of the vessel (65). Suprasternal imaging (66) permits the most extensive echocardiographic visualization of the two arches, whereas subcostal (67) and high parasternal imaging (68) rely more on deductive interpretation. Although statistically the left arch is much more likely to be hypoplastic than the right, numerous exceptions to that rule necessitate detailed evaluation of each case. Angiography has long been the standard for diagnosis but can be confusing because of overlapping structures. Digital
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subtraction angiography (67) is less invasive but offers less sequential data. Magnetic resonance imaging provides information both noninvasively and together with the important spatial relationships of the vessels, trachea, and esophagus to better permit surgical planning (69).
Surgical division of the vascular ring is indicated in any patient who is symptomatic with airway or esophageal compression or in a patient undergoing surgery for intracardiac disease. The ring should be divided in its smaller limb, usually but not always the left. The decision to divide between left carotid and left subclavian or distal to the left subclavian is usually determined by accessibility and the length of the particular segment. In the absence of an accompanying conotruncal anomaly with a large ventricular septal defect, a ductus arteriosus must be present prenatally. Although the presence of a ductus or ligamentum does not appear to contribute to the severity of tracheal compression by the vascular ring, its importance lies in the surgical management. If the arch is divided but the ligamentum remains intact, there may still be a vascular ring. Thus the surgeon must dissect down to the level of the trachea to be sure that all vascular contributors to a ring have been divided.
Persistent Fifth Aortic Arch [Print Section]
Persistent fifth aortic arch was first reported in man by Van Praagh and Van Praagh in 1969 (70) as a double-lumen aortic arch in which both arches appear on the same side of the trachea, as opposed to double aortic arch in which each arch is on the opposite side. Since the initial report, at least one other variation has been noted, resulting in the following subcategorization of this rare anomaly: Double-lumen aortic arch with both lumina patent and (Fig. 36.18C) atresia or
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interruption of the superior arch with patent inferior (persistent fifth) arch—common origin of all brachiocephalic vessels from the ascending aorta (Fig. 36.18A). Double-lumen aortic arch, in which a "subway" vessel occurs beneath the normal aortic (embryonic fourth) arch, appears to be the more common of the two types (71). This inferior arch extends from the innominate artery to a point opposite the take-off of the left subclavian artery, just proximal to the ductus arteriosus or its remnant. Although frequently associated with major cardiac anomalies, it can be an incidental finding without clinical significance (72,73). Cases of atresia or interruption of the superior arch, with a single arterial trunk giving rise to
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all four brachiocephalic arteries, have had coarctation of the aorta as the cause for presentation (71).
Embryology [Print Section]
Although some animals have been noted to have all six pairs of branchial arches during embryonic development, the fifth pair is often seen as only incomplete arches in man (13), implying a brief appearance with no remnant in the definitive arch system. To understand the contribution of a persistent fifth arch to the development of the definitive arch, a modification to the hypothetic double arch is necessary (Fig. 36.18B, D). In cases of double-lumen aortic arch, the fourth arch persists as the superior arch connecting truncoaortic sac to dorsal aorta, and the fifth (inferior) arch does the same (Fig. 36.18D). With atresia or interruption of the superior arch, the fourth arch serves as the connection between carotid and subclavian artery, similar to an innominate artery, but ipsilateral to the definitive arch, which is the fifth arch. The portion of the dorsal aorta between the entrance of the fourth and fifth arches is atretic or disappears completely (Fig. 36.18B).
Diagnosis and Management [Print Section]
Double-lumen aortic arch has been recognized either by angiography or at postmortem examination, with the appearance of a subway vessel beneath the normal arch. This can also be seen with MRI as well, in coronal or off-axis sagittal (candy cane) sections, since axial slices have to be thin enough to resolve the small gap between the two arches (73). In atresia or interruption of the superior arch, there is the appearance of a truly common brachiocephalic trunk in which all four arch vessels, including the left subclavian artery, arise from a single vessel (Fig. 36.18A). In this situation, the branching pattern alone is the indication of a persistent fifth arch since the atretic dorsal aortic extension of the fourth arch cannot be visualized. However, at surgery for repair of coarctation of the aorta (distal to the fifth arch), an atretic strand connecting the left subclavian artery to the descending aorta may be seen. There appears to be no other plausible explanation for such a branching pattern. Without additional coarctation of the existing aorta, these two arch anomalies alone have no physiologic significance.
Interrupted Aortic Arch [Print Section]
Interrupted, or congenitally absent, aortic arch is defined as a complete separation of ascending and descending aorta. It comprises several different anomalies, which generally relate to the pattern of branching of the brachiocephalic arteries. There are at least nine theoretically possible branching patterns. Celoria and Patton (74) classified these as type A if the interruption was distal to the left subclavian artery, type B if between carotid and subclavian arteries, and type C if between carotid arteries. However, these types may be further subcategorized (75) and definitions generalized to include both right and left arch patterns as follows:

Interruption distal to that subclavian artery that is ipsilateral to second carotid artery (i.e., if first carotid is right, interruption distal to left subclavian artery)
Without retroesophageal or isolated subclavian artery
With retroesophageal subclavian artery
With isolated subclavian artery
Interruption between second carotid and ipsilateral subclavian artery
Without retroesophageal or isolated subclavian artery
With retroesophageal subclavian artery (i.e., both carotid arteries proximal, both subclavians distal) (Fig. 36.19A)
With isolated subclavian artery
Interruption between carotid arteries
Without retroesophageal or isolated subclavian artery
With retroesophageal subclavian artery
With isolated subclavian artery

The order of brachiocephalic artery branching suggests a right or left aortic arch pattern following the conventions of noninterrupted arches: In general, the first branch of the aorta proximal to the interruption contains the carotid artery opposite the side of the presumptive arch; a retroesophageal or isolated subclavian artery is always opposite the side of the presumptive arch. The significance of sidedness of the presumptive arch in cases of interruption is the finding that interrupted right aortic arch is apparently seen only in association with DiGeorge syndrome (76).
Type A interruptions tend to occur with aorticopulmonary septal defect and intact ventricular septum (77); they are seen in a disproportionately large subgroup of patients with transposition of the great arteries and interrupted aortic arch (75). Type B interruptions are much more common than type A and usually have a conotruncal anomaly with normally aligned great arteries in which there is a large malalignment-type ventricular septal defect associated with posterior displacement of the infundibular septum and subaortic obstruction. Those patients with DiGeorge syndrome and interruption have type B. Type C interruption is quite rare, permitting no general conclusions about associations.
Embryology [Print Section]
The etiology of interrupted aortic arches can be thought of in terms similar to those that describe the formation of the other arch anomalies discussed above. Type A interruptions show involution of both dorsal aortae distal to the fourth arches and proximal to the persistent sixth arch, which supplies the descending aorta in place of the fourth arch (Fig. 36.19C). Type B interruptions show involution of one fourth arch and one dorsal aorta between arches four and six (Fig. 36.19D) or, in the frequent variant with both subclavian arteries distal to the interruption, involution of both fourth arches and the sixth arch contralateral to the descending aorta (Fig. 36.19B). Type C interruption entails involution of one limb of the truncoaortic sac and its associated proximal third arch and entire fourth arch with persistence of the normally involuted dorsal aorta between arches three and four, the so-called ductus caroticus (Fig. 36.19E).
Virtually all cases of interruption between carotid and subclavian arteries (type B) are associated with a conotruncal anomaly in which hypoplasia of the subaortic region causes subaortic obstruction and a conal septal malalignment type of ventricular septal defect (78). The pathophysiology of the interruption is thought to be an absolute decrease in left ventricular output to the ascending aorta (owing to the combination of outflow obstruction and VSD) with maintenance of normal cerebral perfusion, resulting in a
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relatively large decrease in flow through the aortic arches beyond the takeoff of one or both carotid arteries. The contributing factors that determine precisely which combination of arch involutions occur in each case are not understood. In a large series of cases with DiGeorge syndrome (79), 43% were found to have type B interrupted aortic arch, and 68% of interrupted arch patients had DiGeorge syndrome. This contrasts with truncus arteriosus communis in which comparable figures were 34% and 33%, respectively. Again we see the predisposition to fourth arch abnormality in 22q11 patients. Cases in which subaortic obstruction is not present to explain arch involution are not well understood but may well relate to primary neural crest cell direct influence on the aortic arches themselves.
Diagnosis and Management [Print Section]
These patients typically present, similarly to patients with other ductal-dependent left heart obstructive lesions, with acute cardiovascular collapse or heart failure after spontaneous closure of the ductus arteriosus in the first days of life. Initial management entails fluid resuscitation, induction and maintenance of ductal patency with prostaglandin E1, and establishment of stable hemodynamics, with inotropic support if necessary. Physical findings of pulse discrepancy, depending on branching pattern, are helpful only after restoration of satisfactory cardiac output. Absence of all limb pulses suggests interruption type B with anomalous subclavian artery, i.e., both carotid arteries proximal, both subclavians distal to the interruption. Strong carotid pulses help to differentiate interrupted arch from critical aortic stenosis in which all pulses are diminished. Differential cyanosis (pink upper body, blue lower body), although theoretically possible, is uncommonly seen since pulmonary arterial blood (hence ductal blood) is relatively highly saturated because of the large left-to-right shunt through the VSD. Currently, two-dimensional echocardiography is the most important tool for diagnostic imaging of interrupted arch. The diagnosis should be suspected from the marked discrepancy in size between ascending aorta and main pulmonary artery (80) with subcostal frontal imaging, in the presence of the typical malalignment type VSD with posterior deviation of the infundibular (conal) septum, best visualized in the parasternal long-axis view. Imaging of the arch entails determination of the branching pattern and notation of patency of the arch from suprasternal or high parasternal imaging (81). The smooth superior course of the carotid artery origins, especially in type B interruptions, in contrast to the usual posterior course of an intact aortic arch, is a further clue to the presence of interruption. Angiography is still used in many centers to confirm the diagnosis of interrupted aortic arch; however, torrential flow through a VSD makes it difficult to obtain high-quality imaging of the ascending aorta to distinguish between interruption and severe arch hypoplasia. Interruption can be diagnosed consistently by angiography when both carotid arteries arise proximal to, and both subclavian arteries distal to, the interruption (and ductus). The wide separation of carotid arteries from descending aorta unequivocally demonstrates interruption. Three-dimensional reconstruction from MRI can demonstrate the branching pattern and the separation between proximal and distal aorta (Fig. 36.19A).
The surgical approach to treatment depends on the degree of subaortic obstruction. Subaortic diameters of ≥5 to 6 mm seem to be compatible with primary intracardiac repair, namely patch closure of the VSD, plus aortic arch reconstruction. Subaortic regions of ≤3 mm are inadequate to support normal cardiac output in a full-term infant. In the case of normally aligned great arteries, the subaortic obstruction must be bypassed. The preferred method is to associate the proximal main pulmonary artery with ascending aorta using homograft augmentation to complete the aortic reconstruction, similar to that used for hypoplastic left heart syndrome (Norwood operation) (82). Pulmonary blood flow is provided by a Gore-Tex tube graft from the reconstructed aorta if the VSD is left open, or by a right ventricle-to-pulmonary artery confluence conduit if the ventricles are separated by a baffle from left ventricle to pulmonary valve via the VSD. When interrupted aortic arch is associated with transposition of the great arteries, arterial switch operation is combined with transannular patch across the neopulmonary outflow. Pulmonary artery banding is not a satisfactory palliation of VSD with interrupted aortic arch because it frequently results in biventricular hypertrophy with progressive subaortic stenosis, thus complicating definitive repair by any method at a later date.
The aortic arch itself can almost always be reconstructed by liberal dissection around the two arch components with direct anastomosis of the two ends (83) plus homograft augmentation of the reconstructed arch when necessary to achieve adequate arch size. Artificial tube grafts connecting proximal and distal aorta should be avoided in the initial operation in infancy, if possible, since they are rapidly outgrown, and with fibrous tissue encasement of the native aorta, complicate primary end-to-end anastomosis at a later date.
Other Anomalies of the Aortic Arch System [Print Section]
Anomalous Origin of the Pulmonary Artery from the Ascending Aorta [Print Section]
Anomalous pulmonary artery branch arising from the ascending aorta in the presence of a main pulmonary artery arising separately from the heart is a rare anomaly. Although the term "hemitruncus" has been used, this lesion should be distinguished from true truncus arteriosus communis, with only one pulmonary artery branch arising in common with the ascending aorta and the other arising from a ductus or systemic collateral vessel from the descending aorta.
By far the more common form is anomalous origin of the right pulmonary artery, seen in 82% of 108 cases of an excellent review by Kutsche and Van Mierop (84). All had left aortic arch; many had patent ductus arteriosus; few had tetralogy of Fallot. Interrupted aortic arch distal to the left subclavian artery or coarctation of the aorta were present in 14% of those where the pulmonary artery arose just above the aortic valve, and 8 of 11 of those had an aorticopulmonary septal defect. In contrast, anomalous origin of the left pulmonary artery was associated with tetralogy of Fallot in 74%, and all cases had either tetralogy or right aortic arch or both. No cases of aorticopulmonary septal defect or interrupted aortic arch were present.
Embryology
The rather dramatic difference in associations between anomalous left and right pulmonary artery origins suggests different embryologic mechanisms. Kutsche and Van Mierop (84) propose that in anomalous origin of the right pulmonary artery, the embryonic branch pulmonary artery joins the truncoaortic
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sac (at its right side) but fails in leftward migration to reach the main pulmonary artery portion before septation occurs. They point out that this probably accounts for the significant incidence of aorticopulmonary septal defect. The mechanism of anomalous origin of the left pulmonary artery may be failure of the embryonic branch pulmonary artery to join the truncoaortic sac (or subsequent separation from it) in association with absence of the left sixth (ductal) arch and perhaps persistence of the left fifth arch, whereby the left pulmonary artery becomes associated with the ascending aorta.
Diagnosis and Management
The clinical presentation of anomalous origin of a pulmonary artery branch from the ascending aorta is predominantly that of congestive heart failure in infancy followed by the development of pulmonary vascular disease as early as 6 months of age, if unrepaired. In some patients, there may be an abbreviated (or no) period of clinical heart failure, in which case they may go on to develop pulmonary vascular obstructive disease without warning. Although many have a significant systolic murmur from turbulent, increased pulmonary blood flow, some have little or no murmur and only a loud, narrowly split or single second heart sound to suggest the abnormality. The above findings may be tempered by the relatively infrequent association with other major anomalies such as tetralogy of Fallot or interrupted aortic arch.
The chest roentgenogram may show differential pulmonary vascular markings, especially when superimposed on decreased flow in association with tetralogy of Fallot. Echocardiography is diagnostic, but one must be aware of the potential for mistaking right pulmonary artery merging posteriorly with aorta for normal confluence with main pulmonary artery when using a subcostal frontal sweep. Imaging in multiple views including parasternal short-axis permits differentiation of the pulmonary artery bifurcation from the juncture of right pulmonary artery with ascending aorta. In the case of the very uncommon origin of left pulmonary artery, the rule of thumb is to carefully search for all possible origins of both pulmonary artery branches in the face of tetralogy of Fallot. The more lateral origin of the left pulmonary artery from the ascending aorta also makes imaging of this abnormality easier. Cardiac catheterization usually shows pulmonary hypertension in both pulmonary arteries, although only one can be entered from the right ventricle via the main pulmonary artery. Angiographic demonstration is possible with a left ventriculogram but requires an ascending aortogram if there is a VSD. In patients with unexplained pulmonary hypertension, aortic root injection to rule out origin of a pulmonary artery branch from the ascending aorta or the physiologically similar aorticopulmonary septal defect should be considered. Although MRI can be diagnostic, at present it cannot be used to quantify pulmonary vascular resistance. Treatment consists of surgical division of the anomalously connected pulmonary artery branch and anastomosis directly, or with a graft, to the main pulmonary artery. This should be carried out as early as possible to avoid the development of pulmonary vascular disease.
Anomalous Origin of the Left Pulmonary Artery from the Right Pulmonary Artery [Print Section]
Origin of the left pulmonary artery from the right pulmonary artery, also known as anomalous left pulmonary artery, or pulmonary artery sling (85), is a rare anomaly in which the lower trachea is partially surrounded by vascular structures: The left pulmonary artery arising as a very proximal branch of the right loops around the trachea. It is the only situation in which a major vascular structure passes between the trachea and esophagus. Pulmonary sling is frequently associated with complete cartilaginous rings in the distal trachea (86) resulting in tracheal stenosis, which may require direct surgical treatment in addition to relief from vascular compression. It usually appears as an isolated abnormality but can be associated with other congenital cardiac defects, including tetralogy of Fallot.
Embryology
The distal pulmonary arteries normally arise from their respective lung buds and join the pulmonary artery portion of the truncoaortic sac separately. If the two distal arteries join each other by incorporation of potential vascular islets from the splanchnic bed before becoming incorporated into the truncoaortic sac, one possibility is that the left pulmonary artery would pass behind the trachea before making this juncture. This would result in pulmonary artery sling. If it passed in front of the trachea, this would be indistinguishable from the normal situation.
Diagnosis and Management
These patients typically present with severe respiratory distress and stridor, although milder forms do exist and may be identified incidentally during imaging for another cardiovascular anomaly. Barium swallow when classic (Fig. 36.20A) is diagnostic if one can rule out mediastinal tumor. However, nondiagnostic barium swallows are common, and more definitive testing with either echocardiography, angiocardiography, MRI, or CT (Fig. 36.20C) is usually necessary to ensure the accuracy of the diagnosis. Symptomatic patients should be evaluated by bronchoscopy at the time of surgical repair because of the frequent association of complete cartilaginous rings. The usual surgical approach is division of the left pulmonary artery from the right and reanastomosis in front of the trachea. Alternatively, Jonas et al. (87) have recommended leaving the pulmonary artery and its branches intact while transecting the trachea, mobilizing it behind the pulmonary artery bifurcation and reanastomosing it. If complete cartilaginous tracheal rings are present, tracheal reconstruction may also be necessary. The latter approach is more amenable in that case since the trachea is already opened.
Innominate Artery Compression of the Trachea [Print Section]
Innominate artery compression of the trachea or so-called anomalous innominate artery is a poorly understood abnormality in which there is anterior compression of the trachea at the point where it is crossed by the innominate artery. Some have thought this due to a more distal, that is, leftward, takeoff of the innominate artery from the aortic arch; however three-dimensional reconstructions from MRI have not demonstrated any consistent abnormality of the aorta or its branching pattern. The presumed abnormality is tracheomalacia, whether idiopathic or in association with tracheoesophageal fistula (88), with the innominate artery in the vicinity of the malacic segment of trachea. The diagnosis is suspected when signs of severe inspiratory and expiratory stridor, usually in a 2- to 6-month-old child, are associated with anterior indentation of the tracheal air column on lateral chest roentgenogram.
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However, vascular rings should be ruled out with at least a barium esophagram. Simultaneous visualization of the innominate artery and the trachea is afforded by MRI and is shown dramatically with three-dimensional reconstruction (Fig. 36.21). Treatment usually entails waiting for the tracheomalacia to resolve, typically by age 2 years; however, in cases associated with apnea or repeated lower respiratory infections, surgical sectioning of the innominate artery and reimplantation more proximally, i.e., rightward in the aorta may be helpful. In limited cases suspension of the sternum has been used, but there is often little room behind the sternum to relieve pressure on the trachea.