Vascular Rings, Slings, and Other Arch Anomalies
Christopher E. Mascio
Erle H. Austin
HISTORICAL ASPECTS
Recognition of anomalies of the aortic arch and pulmonary artery began in 1737 when Hommel first described a double aortic arch. Fifty-seven years later, Bayford discovered an aberrant retroesophageal subclavian artery in a patient with a history of dysphagia. He called the anomaly a “lusus naturae,” or “prank of nature,” and coined the term “dysphagia lusoria” to describe the symptoms. The first surgical correction of a double aortic arch was performed by Gross in 1945 on a 1-year-old boy with chronic wheezing. The pulmonary arterial sling anomaly was described by Glaevecke and Doehle in 1897 and was first repaired by arterial division with reimplantation by Potts in 1954.
EMBRYOLOGY
By 5 weeks of fetal development, the primordial heart tubes have fused and six aortic (branchial) arches have formed between the ventral roots and dorsal aortae (Fig. 78.1). Migration and involution of the arches result in the complex system of the higher mammal. During normal development, persistence of the left fourth aortic arch forms the arch of the aorta between the left common carotid and left subclavian arteries. The right fourth aortic arch forms the proximal right subclavian artery. Involution of the distal right aorta results in an unpaired single aortic arch. Table 78.1 shows the fate of the remaining arches.
Failure of involution or migration of specific segments of the aortic arches results in anomalies that may form partial or complete vascular rings about the trachea and esophagus. The most common of these are diagrammed in Fig. 78.2.
Pulmonary artery development arises from two separate vascular sources: (1) the lung buds deriving their blood supply from the splanchnic plexus and (2) the proximal left and right sixth aortic arches (Fig. 78.3). Figure 78.4 demonstrates how abnormal migration of the separate blood supplies can result in dislocation of the left pulmonary artery posterior to the trachea, resulting in the pulmonary artery sling anomaly with its associated tracheal compression.
CLASSIFICATION AND INCIDENCE
Aortic arch anomalies producing tracheoesophageal constriction account for 1% to 2% of all congenital heart defects. A simple and commonly used system of classifying these vascular anomalies is given in Table 78.2. The relative prevalence of these lesions in surgical series is also indicated.
Group I: Complete Vascular Rings Anatomy
A double aortic arch (type IA) occurs when the right dorsal aorta fails to involute (Fig. 78.2), resulting in persistence of the right and left fourth aortic arches. The right aortic arch is most commonly dominant. The descending aorta is usually in its normal position on the left, as is the ligamentum arteriosum (or patent ductus arteriosus). Generally, each subclavian and common carotid artery arises independently from its respective aortic arch. The innominate vessels do not develop. Twenty percent of cases have other cardiac anomalies, with ventricular septal defect and tetralogy of Fallot being most common.
Type IB vascular rings (right aortic arch with retroesophageal ligamentum arteriosum) account for 45% of complete vascular rings. The majority of these defects have left descending aortas. A right aortic arch with retroesophageal left subclavian artery and ligamentum results from abnormal involution of the left fourth arch. A remnant or stump of the left fourth arch (Kommerell’s diverticulum) may persist. The left subclavian artery arises aberrantly behind the esophagus from the right-sided arch or from Kommereli’s diverticulum. Near this point, the left-sided ligamentum emanates and joins the left pulmonary artery to create a complete ring about the trachea and esophagus. Another variant of right aortic arch with left descending aorta is called the circumflex aorta. This variant is characterized as having a hypoplastic retroesophageal arch and a coarctation (Fig.78.9A and 78.9B).
A right aortic arch may occur with mirror image branching with the left innominate artery arising anteriorly and dividing into the left carotid and subclavian arteries. If the ligamentum arteriosum occurs between the left innominate artery and the left pulmonary artery, as is commonly seen in association with tetralogy of Fallot, there is no vascular ring. Therefore, these patients are usually asymptomatic. However, when the ligamentum arises from the aorta behind the esophagus and connects with the left pulmonary artery, a compressive vascular ring is formed.
A rare variant among vascular rings is the cervical aortic arch, in which case the arch exists in the neck above the clavicle, sometimes as high as the C2 vertebral body. There are two main subtypes. The first and the larger group are type IB anomalies with a right-sided arch, an anomalous left subclavian artery, and a retroesophageal ligamentum arteriosum. The second group has a left-sided arch with a normal branching pattern and thus does not form a complete ring. These anomalies are thought to result from a failure of the normal descent of the aortic arch from its cephalic location at 3 weeks to its intrathoracic location at 7 weeks of gestation.
Clinical Presentation
The clinical presentation of vascular rings can vary from mild dyspnea or dysphagia to respiratory distress and apnea. Signs and symptoms often depend on the type of anomaly.
A double aortic arch produces the earliest and most severe symptoms as a result of the presence of a tight ring around
the trachea and esophagus. Seventy-five percent of affected patients develop symptoms by 1 year of age, often within the first month of life and rarely after 6 months of age. Stridor, a nonproductive cough, or a hoarse cry may be noted soon after birth. The stridor generally worsens with feedings, especially solid foods. The cough is characterized as a “seal bark” or “brassy cough.” Respiratory distress can lead to choking, cyanosis, and apnea. Vomiting may precede or follow choking. Despite the esophageal compression, most infants with double aortic arch tolerate liquids well and appear well fed.
the trachea and esophagus. Seventy-five percent of affected patients develop symptoms by 1 year of age, often within the first month of life and rarely after 6 months of age. Stridor, a nonproductive cough, or a hoarse cry may be noted soon after birth. The stridor generally worsens with feedings, especially solid foods. The cough is characterized as a “seal bark” or “brassy cough.” Respiratory distress can lead to choking, cyanosis, and apnea. Vomiting may precede or follow choking. Despite the esophageal compression, most infants with double aortic arch tolerate liquids well and appear well fed.
 Fig. 78.1. Normal aortic arch development. The normal aortic arch arises from the persistence of the left fourth embryologic arch. Note that the recurrent laryngeal nerve recurs about the derivative of the sixth embryologic arch on the left, that is, the ductus arteriosus, and the derivative of the fourth embryologic arch on the right, that is, the right subclavian artery. This occurs because of the normal involution of the right sixth embryologic arch. a., artery; Ao, aorta; car., carotid; com., common; Duct. art., ductus arteriosus; Esoph., esophagus; ext., external; int., internal; L., left; LPA, left pulmonary artery; n., nerve; PA, pulmonary artery; R., right; Rec. laryn. nn., recurrent laryngeal nerves; RPA, right pulmonary artery; subcl., subclavian. |
Table 78.1 Outcome of the Embryonic Aortic Arches | |||||||||||||||||||||||||||||||||||||||||||||||||
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When tracheoesophageal compression results from a right aortic arch and a retroesophageal ligament, symptoms are similar in nature but are usually less severe and present later in infancy or in early childhood. These rings are generally less stenotic and become notable as the aorta grows.
Those with a right arch and left descending aorta (circumflex aorta) may present with murmur, upper extremity blood pressure differential, exertional dyspnea, and/or chest pain.
Patients with cervical arches are usually asymptomatic but may present with a pulsatile mass in the neck or the
supraclavicular fossa. Infants with the type IB anomaly may also exhibit the compressive symptoms of dyspnea and stridor. Adults more commonly present with dysphagia. Some adults have presented with central nervous system symptoms and the subclavian steal syndrome as a result of stenoses of the left subclavian artery and origin of the vertebral artery.
supraclavicular fossa. Infants with the type IB anomaly may also exhibit the compressive symptoms of dyspnea and stridor. Adults more commonly present with dysphagia. Some adults have presented with central nervous system symptoms and the subclavian steal syndrome as a result of stenoses of the left subclavian artery and origin of the vertebral artery.
 Fig. 78.2. Vascular rings most frequently requiring surgical intervention and their embryologic development. Kommerell’s diverticulum is a remnant of the involuted left fourth aortic arch, which may be the origin of the ductus (ligamentum), the left subclavian artery, or both. a., artery; Ao, aorta; L. ext. car. a., left external carotid artery; L. int. carotid. a., left internal carotid artery; LCCA, left common carotid artery; Lig. art., ligamentum arteriosum; LSA, LSCA, left subclavian artery; PA, pulmonary artery; PDA, patent ductus arteriosus; RCCA, right common carotid artery; RSA, RSCA, right subclavian artery; roman numerals refer to embryologic aortic arches. |
 Fig. 78.2. |
Diagnosis
A vascular ring may be suggested on chest radiography by the presence of a pulmonary infiltrate, atelectasis, or unilateral or bilateral hyperinflation. The presence of a right aortic arch should raise suspicion.
Barium esophagogram remains a useful diagnostic measure. In cases of double aortic arch, the lateral view will reveal a posterior indentation in the esophagus. In the anterior projection, there are dual indentations, higher on the right and lower on the left. An aberrant right subclavian artery from a left aortic arch will also produce posterior esophageal indentation on the lateral view. On the anterior view, however, the aberrant right subclavian artery takes an oblique course descending left to right. The aberrant retroesophageal left subclavian artery from a right aortic arch will show a similar posterior indentation on the lateral view, but the oblique course on the anterior view runs in the opposite direction: from right to left. A circumflex aorta (right arch and left descending aorta) will have an impression on the right side of the esophagus on the anterior view and a deep, posterior indentation on the lateral view.
Historically, the clinical presentation and barium esophagogram have provided sufficient information to proceed to surgical treatment. The increasing availability and sophistication of magnetic resonance imaging (MRI) and computed tomography (CT), however, have elevated these noninvasive imaging techniques to the preferred diagnostic modality at most institutions. Both modalities provide detailed and complete depiction of the anatomy and compressive effects of a vascular ring. MRI, however, is expensive and requires sedation in the younger patients who are at the greatest risk from airway compression. Without sedation, motion artifacts frequently result in poor image quality. Traditional CT scanning with three-dimensional reconstruction can also provide excellent images
but is limited by the need for intravenous contrast and exposure to radiation and may also require sedation for adequate imaging. Rapid, multislice, helical CT scanning (if available) permits rapid scanning with significantly decreased radiation exposure. These scans can be done in <2 seconds in infants, obviating the need for sedation. Aortography is the most invasive technique and is rarely used. It can establish the completeness of a double aortic arch and identify areas of luminal irregularity. It cannot, however, distinguish between a double aortic arch with an atretic segment and a right aortic arch with a retroesophageal ligament. Transthoracic echocardiography is used to detect associated cardiac anomalies and is reasonably sensitive in evaluating vascular rings but appears deficient in determining atretic and nonluminal segments. Echocardiography is important in defining any other associated cardiac anomalies. As mentioned above, these are present in up to 20% of patients and are more common in association with right aortic arch (compared with double aortic arch).
but is limited by the need for intravenous contrast and exposure to radiation and may also require sedation for adequate imaging. Rapid, multislice, helical CT scanning (if available) permits rapid scanning with significantly decreased radiation exposure. These scans can be done in <2 seconds in infants, obviating the need for sedation. Aortography is the most invasive technique and is rarely used. It can establish the completeness of a double aortic arch and identify areas of luminal irregularity. It cannot, however, distinguish between a double aortic arch with an atretic segment and a right aortic arch with a retroesophageal ligament. Transthoracic echocardiography is used to detect associated cardiac anomalies and is reasonably sensitive in evaluating vascular rings but appears deficient in determining atretic and nonluminal segments. Echocardiography is important in defining any other associated cardiac anomalies. As mentioned above, these are present in up to 20% of patients and are more common in association with right aortic arch (compared with double aortic arch).
 Fig. 78.3. Normal pulmonary artery development. The pulmonary arteries derive from two separate vascular buds, the sixth aortic arches (left and right) and the splanchnic plexus. These buds fuse to form the left and right pulmonary arteries. Ao, aorta; L., left; Lig. art., ligamentum arteriosum; LPA, left pulmonary artery; LV, left ventricle; PA, Pulm. art., pulmonary artery; R., right; RA, right atrium; RPA, right pulmonary artery; RV, right ventricle. |
Cervical arches may be suspected by the presence of a wide mediastinum, the absence of the aortic knob, and anterior tracheal deviation on chest radiography. Although angiography has been the standard for diagnosis, CT scanning and MRI now provide a noninvasive technique to confirm the diagnosis.
Indications for Surgery
Surgical correction of complete vascular rings is indicated when symptoms are present. There is no evidence that surgery has any benefit in the absence of symptoms, thus asymptomatic patients (children or adults) should not be exposed to the operative risk. Adults with minimal symptoms should be followed for significant progression prior to operative repair. Anomalies identified shortly after birth or within the first 6 months of life require surgical correction much more frequently than those discovered after the age of 6 months. Very mild symptoms presenting in the older infant or young child may resolve as the child grows. A watchful approach is appropriate in such cases.
Surgical Technique
Ninety percent of vascular ring cases can be corrected through a left posterolateral thoracotomy. Single-lumen general endotracheal anesthesia is applied.
Double aortic arch: In cases of double aortic arch, where flow is present in both arches, the dominant arch is preserved. Division is performed at the location on the ring that preserves the greatest brachial and cephalic flow. When an atretic segment of the vascular ring is present, division is performed at the atretic segment. Before vascular division, the carotid and radial pulses are monitored by the anesthesiologist to confirm flow after clamps have been placed.
After induction of general orotracheal anesthesia, the infant is placed in a full lateral position with the left side up (Fig. 78.5). Through a posterior lateral muscle-preserving incision, the left chest is entered through the third or fourth intercostal space. The lung is retracted anteriorly and inferiorly, exposing the posterior mediastinum. This position is retained with malleable retractors secured to the chest retractor with nonpenetrating towel clamps.
 Fig. 78.4. Anomalous development of the left pulmonary artery and formation of the pulmonary artery sling. When the splanchnic bud of the left pulmonary artery fails to fuse with the left sixth aortic arch, it migrates posteriorly between the trachea and esophagus to fuse with the right pulmonary artery. This results in a compressive “sling” about the trachea. Anom., anomalous; LPA, left pulmonary artery; RPA, right pulmonary artery. |
The descending aorta, anterior (left) aortic arch, left subclavian artery, and the vagus and phrenic nerves are identified before the pleura is opened (Fig. 78.5). The vagus nerve descends anterior to the left subclavian artery, crossing the left aortic arch, giving off the recurrent laryngeal nerve as it penetrates into the mediastinum medially around the ligamentum arteriosum. The posterior (right) aortic arch may or may not be visualized initially depending on the extent of mediastinal fat.
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