Park's Pediatric Cardiology for Practitioners, 6th Ed.

Vascular Ring

Prevalence

Vascular ring reportedly represents less than 1% of all congenital cardiovascular anomalies, but this may be an underestimate because some conditions are asymptomatic.

Pathology

Vascular ring refers to a group of anomalies of the aortic arch that cause respiratory symptoms or feeding problems. A rare anomaly of the left pulmonary artery L(PA) that causes symptoms is also included in this group, although it does not involve the aortic arch. The vascular ring may be divided into two groups, complete (or true) and incomplete.

1. Complete vascular ring refers to conditions in which the abnormal vascular structures or their remnants form a complete circle around the trachea and esophagus. Double aortic arch and right aortic arch with left ligamentum arteriosum are examples of complete vascular ring.

2. Incomplete vascular ring refers to vascular anomalies that do not form a complete circle around the trachea and esophagus but do compress the trachea or esophagus. These include anomalous innominate artery, aberrant right subclavian artery, and anomalous left PA (“vascular sling” or “pulmonary sling”).

Five major vascular rings will be discussed in this chapter.

1. Double aortic arch is the most common vascular ring (40%) (Fig. 16-1). This anomaly is caused by a failure of regression of both the right and left fourth branchial arches, resulting in right and left aortic arches, respectively. These two arches completely encircle and compress the trachea and esophagus, producing respiratory distress and feeding problems in early infancy. The right arch gives off two arch vessels, the right common carotid and the right subclavian arteries, and the left arch gives off the left common carotid and left subclavian arteries (see Fig. 16-1). The right aortic arch is usually larger than the left arch (seen in 75% of patients), but on rare occasions, partial obstruction or complete atresia of the left arch (with a ligamentous remnant) may occur. Double aortic arch is commonly an isolated anomaly but is rarely associated with a variety of congenital heart defects (CHDs) such as transposition of the great arteries, ventricular septal defect (VSD), persistent truncus arteriosus, tetralogy of Fallot (TOF), and coarctation of the aorta (COA).

2. Right aortic arch with left ligamentum arteriosum. One of the major components of most vascular rings is a right aortic arch. Vascular ring with a right arch with left ligamentum arteriosum has several different forms; two common types are described here. Although rare, right aortic arch may occur without forming a vascular ring if the aorta stays and descends on the right of the vertebrae.

a. In the most frequent form of vascular ring with right aortic arch with left ligamentum arteriosum (occurring in ≈65% of cases), the right arch first gives off the left carotid artery, then the right carotid artery followed by the right subclavian artery, and last, the left subclavian artery (see Fig. 16-1). The aberrant left subclavian artery often arises from a retroesophageal diverticulum (called diverticulum of Kommerell). The ring is completed by a left-sided ductus arteriosus (or its remnant ligamentum arteriosum) passing from the subclavian artery to the proximal LPA (see Fig. 16-1). The descending aorta usually courses to the left of the vertebral column to pass through the diaphragm in the usual location of the aortic hiatus. About 10% of this type of vascular ring is associated with an intracardiac defect.

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FIGURE 16-1 Clinical summary of vascular ring. In the anatomy of right aortic arch with left ligamentum arteriosum (in the second row), thick short black bands (indicated by thick arrows) are left-sided ductal ligaments. Aber., aberrant; Ba-Esophag., barium esophagogram; Lat., lateral view; Lig., ligamentum; LPA, left pulmonary artery; MPA, main pulmonary artery; P-A, posteroanterior view; Post., posterior; RPA, right pulmonary artery; Rt., right; Subclav., subclavian.

As a rare variant of this type, an aberrant innominate artery, rather than subclavian artery, may arise from the upper descending, and the ligamentum arteriosum connects the base of the innominate artery and the proximal left PA completing a vascular ring. Clinical manifestations are similar to the one described above.

b. In the second type of vascular ring with right aortic arch and ligamentum arteriosum (occurring in ≈35%), the left innominate artery originates from the right arch in mirror image fashion as the first branch followed by the right carotid and right subclavian arteries. A left-sided ductus or ligamentum arteriosum passes between the descending aorta and the proximal LPA (see Fig. 16-1). More than 90% of patients with this type of vascular ring have associated intracardiac defects, notably TOF and truncus arteriosus.

3. Anomalous innominate artery occurs in about 10% of patients with vascular ring (see Fig. 16-1). If the innominate artery takes off too far to the left from the aortic arch or more posteriorly, it may compress the trachea, producing mild respiratory symptoms. This anomaly is commonly associated with other congenital heart defects such as VSD.

4. Aberrant right subclavian artery is the most common arch anomaly (accounting for 0.5% of the general population, but its true incidence may be higher if asymptomatic patients are included). Most cases are asymptomatic. When the right subclavian artery arises independently from the descending aorta, it courses behind the esophagus, compressing the posterior aspect of the esophagus and producing mild feeding problems (Figs. 16-1 and 16-2). Often, a larger compression is found behind the esophagus by an aortic diverticulum at the take-off of the right subclavian artery. This anomaly usually is an isolated anomaly, but it has a high association with coarctation of the aorta or interrupted aortic arch. Its incidence is very high (38%) in patients with Down syndrome with CHDs.

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FIGURE 16-2 Barium esophagogram in a child with aberrant right subclavian artery. A, Anteroposterior view shows an oblique indentation of the esophagus (arrow) at the level slightly higher than the carina produced by the subclavian artery. The indentation proceeds upward and to the right toward the right shoulder. B, Lateral projection shows a relatively shallow, long retroesophageal impression produced by the aberrant artery.

5. Anomalous left PA (also called “vascular sling” ) is a rare anomaly in which the left PA arises from the right PA (Figs. 16-1 and 16-3). To reach the left lung, the anomalous artery courses over the proximal portion of the right mainstem bronchus, behind the trachea, and in front of the esophagus to the hilum of the left lung. Therefore, both respiratory symptoms and feeding problems (e.g., coughing; wheezing; stridor; episodes of choking, cyanosis, or apnea) may occur. About 10% to 20% of patients with this anomaly have associated cardiac defects, such as patent ductus arteriosus, VSD, atrial septal defect (ASD), atrioventricular canal, single ventricle, or aortic arch anomalies.

Clinical Manifestations

History

1. Inspiratory stridor and feeding problems of varying severity are present, beginning at different ages. In double aortic arch, symptoms tend to appear in the newborn period or in early infancy (before 3 months of age), and they are more severe than those in right aortic arch with left ligamentum arteriosum. Symptoms often are made worse by feeding. Affected infants frequently hyperextend their necks to reduce tracheal compression.

2. Respiratory symptoms or feeding problems are milder with incomplete forms of vascular ring than with the complete form.

3. A history of pneumonia frequently is elicited.

4. A history of atelectasis, emphysema, or pneumonia of the right lung is found with “vascular sling.”

Physical Examination

1. Physical examination is not revealing except for a varying degree of rhonchi when the vascular ring is an isolated anomaly.

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FIGURE 16-3 Pulmonary arteriogram in an infant with “vascular sling.” The left pulmonary artery (lpa) arises from the posterosuperior aspect of the right pulmonary artery (rpa) (black arrows) rather than from the main pulmonary artery (mpa). The origin of the left pulmonary artery (lpa) is to the right of the trachea, which is easily identifiable by an endotracheal tube (two rows of white arrows). The esophagus is directly behind the proximal portion of the aberrant left pulmonary artery, which caused an anterior indentation on the barium esophagogram. The esophagus is identifiable by an orogastric tube that was inserted at the time of cardiac catheterization (large white arrows).

2. Cardiac examination is usually normal except in about 25% of patients in whom associated cardiac anomalies are present.

Electrocardiography

The electrocardiography findings are normal unless the vascular ring is associated with other CHDs.

Diagnosis

The diagnosis of vascular ring is accomplished by using the following imaging techniques; some are routinely available and others are specialized.

1. Chest radiography: Because patients usually present with symptoms of respiratory difficulty, chest radiography is always the first and most commonly performed test.

a. One looks for right aortic arch. In right aortic arch, the trachea is deviated to the left of the midline rather than to the right as seen in the presence of a normal left arch. If a right aortic arch is identified, a vascular ring is highly likely. If only a left arch is identified, a vascular right is much less likely but not excluded.

b. An ill-defined aortic arch location is often observed in patients with double aortic arch.

c. With the complete form of vascular ring, compression of the air-filled trachea may be visible on posteroanterior or lateral chest radiography.

d. Aspiration pneumonia may be present. Hyperinflation or atelectasis of the right lung may be a suggestive sign of anomalous LPA (“vascular sling”).

2. Barium esophagography: If plain chest radiography suggests vascular rings, barium esophagography is the next logical step, which is usually diagnostic of most vascular rings (see Fig. 16-1). Patients with normal esophagography findings do not have a significant vascular ring.

a. In double aortic arch, two large indentations are present in both sides (with the right one usually larger) on the posteroanterior view, and a large posterior indentation is seen on the lateral view (see Fig. 16-1).

b. In right aortic arch with left ligamentum arteriosum, a large right-sided indentation and a much smaller left-sided indentation are present. A posterior indentation, either small or large, also is present on the lateral view. A large posterior indentation suggests the presence of diverticulum of Kommerell (see Fig. 16-1).

c. In aberrant right subclavian artery, there is a small oblique indentation extending toward the right shoulder on the posteroanterior view. There is a small posterior indentation on the lateral view (see Figs. 16-1and 16-2). Indentations may be large if the compression is made by an aortic diverticulum.

d. In “vascular sling,” an anterior indentation of the esophagus seen in the lateral view at the level of the carina is characteristic. This is the only vascular ring that produces an anterior esophageal indentation (see Fig. 16-1). A right-sided indentation usually is seen on the posteroanterior view. The right lung is either hyperlucent or atelectatic with pneumonic infiltrations.

e. Barium esophagography findings are normal in anomalous left innominate artery.

3. Echocardiography and color-flow Doppler: Echo and color-flow Doppler studies are very helpful, both for diagnosing vascular ring and for excluding associated intracardiac defects. One should perform a careful segmental investigation of the aortic arch and arch vessels. The suprasternal notch views are especially useful in establishing the diagnosis.

However, there are limitations to echocardiographic study in the diagnosis of vascular ring. Structures without a lumen, such as a ligamentum arteriosum or an atretic arch, have no blood flow and are difficult to identify with color-flow echocardiography. Also, identification of compressed midline structures and their relationship to encircling vascular anomalies is difficult to detect with echo studies.

4. Computed tomography (CT) scan, magnetic resonance imaging (MRI), and digital subtraction angiography: These radiologic studies are often used in the diagnosis of vascular rings and may eliminate the need for invasive aortography.

a. CT and MRI are useful diagnostic tools because they reveal not only the position of vascular structures but also of the tracheobronchial and esophageal structures and their relationships to the vascular structures. These studies do not show ligamentum arteriosum either. MRI has been proposed as an excellent substitute for angiography.

b. These radiologic techniques have advantages and disadvantages. The major advantage of CT is the rapidity with which data can be acquired, in many cases without the need for sedation. Its disadvantage is the use of radiation and need for intravenous contrast media. MRI, on the other hand, does not use radiation or iodinated intravenous contrast media but does have longer imaging times, requiring sedation in most pediatric patients; sedation may be particularly risky in young children with airway obstruction, and general anesthesia with intubation might be required.

5. Aortic angiography and cardiac catheterization: In the past, diagnostic aortography was performed in delineating anomalous arch vasculatures. However, it is more invasive and does not have tomographic or multiplanar capability. Echo with color Doppler studies, CT, or MRI can usually provide the required information before surgery. Therefore, when a choice is available, MRI and CT angiography are preferable for detailed diagnosis and preoperative assessment.

6. Tracheography and bronchoscopy usually add little information and may be hazardous in some patients. However, these tests may be useful in delineating tracheobronchial malacia associated with vascular ring in some patients.

Management

Medical

1. Asymptomatic patients need no surgical treatment even when the anomalies are found incidentally.

2. Medical management for infants with mild symptoms includes careful feeding with soft foods and aggressive treatment of pulmonary infections.

Surgical

Indications and Timing

Respiratory distress and a history of recurrent pulmonary infections and apneic spells are indications for surgical intervention. The timing of surgery depends on the severity of symptoms, and surgery may be performed during infancy.

Procedures and Mortality Rate

1. Double aortic arch: Division of the smaller of the two arches (usually the left) is performed through a left thoracotomy. Knowing which arch is the dominant arch is very important because thoracotomy is typically performed on the side of the nondominant arch. The surgical mortality rate is less than 5%.

2. Right aortic arch and left ligamentum arteriosum: Ligation and division of the ligamentum are performed through a left thoracotomy. If a Kommerell diverticulum is found, the diverticulum is resected, and the left subclavian artery is transferred to the left carotid artery. The mortality rate is less than 5%.

3. Anomalous innominate artery: Through a right anterolateral thoracotomy, the innominate artery is suspended to the posterior sternum. Asymptomatic patients do not require surgery; only 10% of the patients with the anomaly require surgery.

4. Aberrant right subclavian artery: Surgical interruption of the aberrant artery is performed rarely only in symptomatic patients with dysphagia. The procedure consists of division of the aberrant artery and translocation to the right common carotid artery.

5. Anomalous LPA: Surgical division and reimplantation of the left PA to the main PA is performed, usually through a median sternotomy and with the use of cardiopulmonary bypass. The surgical mortality rate is near 0%.

Complications

In infants who have had surgery for severe symptoms, airway obstruction may persist for weeks or months. Careful respiratory management is required in the postoperative period. A period of months to 1 year may be required before disappearance of the noisy respiration, which is caused by preexisting tracheomalacia. This fact should be anticipated and clearly explained to the parents preoperatively. This complication is more likely in patients who have had double aortic arch, vascular sling, or right aortic arch with left ligamentum arteriosum.

Variants of Aortic Arch Branching

Although the most common aortic arch branching pattern is three-vessel branching pattern in humans, up to about 30% of patients have a two-vessel branching pattern, which is a normal variant. The two-vessel branching pattern has incorrectly been called the “bovine aortic arch” in humans. True bovine aortic arch branching has no resemblance to the two-vessel branching patterns seen in humans. Thus, the use of misnomers such as “bovine arch” should be avoided. Instead, one should use descriptive branching patterns as described below or simply call it a two-vessel branching pattern if further branching information is not known (Layton et al, 2006).

The following describes standard aortic arch branching and its normal variants in humans (Fig. 16-4).

1. The most common aortic arch branching pattern (standard aortic arch branching) in humans consists of three great arteries originating from the aortic arch. The first branch is the innominate artery, the second one the left common carotid artery, and the third one the left subclavian artery (Fig. 16-4A). This pattern is present in about 70% of patients.

2. A common variant of the standard aortic arch is the one in which two great arteries originate from the aortic arch. This occurs in about 30% of patients, more commonly observed in Africans. In one group of these patients, the innominate artery and the left carotid artery share the common trunk, which occurs in about 13% of patients (correctly described as “common origin of the innominate artery and left common carotid artery”) (Fig. 16-4B). In the other group of the two-vessel branching variant, the left common carotid artery branches from the innominate artery (rather than sharing the common trunk). This variant occurs in about 9% of patients (correctly described as “origin of the left carotid artery from the innominate artery”) (Fig. 16-4C).

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FIGURE 16-4 Variants in the aortic arch branching pattern in humans and the bovine aortic arch. A, The most common branching pattern found in humans. B, The second most common pattern in humans. C, Less common branching pattern in humans in which the left carotid artery originates from the innominate artery. D, True bovine aortic arch. Brachioceph., brachiocephalic; carot., carotid; Innom., innominate. Lt., left; Rt., right; subcl., subclavian.

In the true bovine aortic arch, there is only one great artery originating from the arch. It has no resemblance to any of the branching patterns seen in humans. The single trunk, called the “brachiocephalic trunk,” gives rise to both subclavian arteries and a bicarotid trunk. The bicarotid trunk then bifurcates into the left and right common carotid arteries (Fig. 16-4D).