Chest Radiography
Because children usually present with symptoms of respiratory difficulty, chest radiography is always the first and most commonly performed test.
Look for the position of the aortic arch, which is usually identifiable on the plain chest radiograph. The identification of a right aortic arch on chest radiograph in a child with airway difficulties, respiratory distress or dysphagia should alert the clinician to the likelihood of a vascular ring.
An ill-defined arch location is often observed in patients with double aortic arch. Such a finding should raise the suspicion of an arch anomaly in a symptomatic child. Other radiographic findings that may be noted with vascular rings include compression of the trachea and hyperinflation or atelectasis of some of the lobes of either lung. A specific finding associated with an anomalous left pulmonary artery is hyperinflation of the right lung.
In general, chest radiography is not very sensitive in the diagnosis of vascular rings.
Barium Esophagography
Most authorities consider barium esophagography to be the most important study in patients with a suspected vascular ring, and it is diagnostic in the vast majority of cases. (See the image below.)
Double aortic arch produces bilateral and posterior compressions of the esophagus, which remain constant regardless of peristalsis. The right indentation is usually slightly higher than the left, and the posterior compression is usually rather wide and courses in a downward direction as it goes from right to left.
Patients with one of the anomalies in which the right subclavian artery takes a retroesophageal course have a posterior defect slanting upward from left to right. The posterior defect in these cases is usually not as broad as that found in double aortic arch.
An anomalous left pulmonary artery produces a characteristic defect in the anterior wall of the esophagus at the level of the tracheal bifurcation. No posterior compression is present with this anomaly. Cases of abnormally located innominate artery causing tracheal compression have normal findings on esophagography.
Echocardiography and Color-Flow Doppler
Echocardiographic studies have been increasingly used for the diagnosis of a vascular ring. [15] At many centers, this study has replaced pulmonary angiography for determining the presence of an anomalous left pulmonary artery. It is also extremely useful in the diagnostic workup of associated congenital cardiac defects.
This study has some diagnostic limitations. 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. In addition, identification of compressed midline structures and their relations to encircling vascular anomalies may be difficult to detect, especially for the less experienced echocardiographer.
The addition of three-dimensional (3D) reconstruction techniques may improve the accuracy of echocardiography in diagnosing fetal aortic arch anomalies. [16, 17] High antenatal detection rates are achievable. [18]
CT, MRI, and DSA
Computed tomography (CT), magnetic resonance imaging (MRI), and digital subtraction angiography (DSA) can be useful diagnostic tools because they reveal the positions of vascular, tracheobronchial, and esophageal structures and their relations to one another. However, these expensive imaging modalities are rarely necessary in the evaluation of vascular rings. [19]
Although CT, MRI, and DSA provide excellent delineation of all of the associated structures, they should be reserved for cases in which the results of barium esophagography do not provide a clear diagnosis. MRI has been proposed as an excellent substitute for angiography. [20] Multidetector CT (MDCT) is increasingly preferred to angiography in this setting. [21]
All of these studies have drawbacks. CT and DSA expose the patient to radiation and require intravenous (IV) contrast. MRI requires patients to remain very still, and thus, very young patients who are unable to understand verbal instructions must be sedated—a measure that may be particularly risky in young children with existing airway compromise. The expense associated with these investigations must also be considered.
Aortography and Cardiac Catheterization
In the past, diagnostic aortography was performed in selected cases to delineate the anomalous arch vasculature. At present, it is generally agreed that in the vast majority of cases, this study adds very little to the information obtained from barium esophagography. If additional studies are required, echocardiography, CT, or MRI can usually provide the information needed.
Nevertheless, cases of rare arch anomalies have been reported in which aortography was the only study capable of identifying the correct anatomic configuration. [22] This study may be required in cases where the diagnosis and arch configuration remain in question after other less invasive studies fail to provide a definitive answer.
Cardiac catheterization is useful in cases where associated cardiac abnormalities are known or suspected.
Procedures
Bronchoscopy has been used in the evaluation of children with symptoms of airway obstruction or compression. It is most commonly applied to the diagnosis of an abnormally placed innominate artery or pulmonary sling but is rarely required in the diagnosis of the various types of complete vascular ring.
In the presence of a vascular ring, pulsatile external tracheal compression is easily observed. Compression of the airway by a vascular structure in the pediatric patient does not represent an unyielding obstruction and should not pose a problem for passage of the bronchoscope. In cases of an abnormally placed innominate artery, obvious pulsation is observed in the anterior wall of the trachea corresponding to the area of compression.
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Slide tracheoplasty and left pulmonary artery sling repair. Procedure performed by Giles Peek MD, FRCS, CTh, FFICM, The Children’s Hospital at Montefiore, Bronx, NY.
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Embryonic aortic arch with dorsal and ventral arches and 6 branchial arches on right and left.
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Double aortic arch.
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Right aortic arch with aberrant left subclavian artery and left ligamentum arteriosum.
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Right aortic arch with mirror-image branching and retroesophageal ligamentum arteriosum.
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Left aortic arch with right descending aorta and right ligamentum arteriosum.
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Retroesophageal right subclavian artery with left aortic arch and left ligamentum arteriosum.
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Aberrant left pulmonary artery or pulmonary artery sling.
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Barium esophagogram of 30-year-old woman with vascular ring.
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Single-stage correction of transposition of great arteries with ventricular septal defect, hypoplastic right aortic arch with bilateral ductuses, and aberrant left subclavian artery arising from left duct in newborn. Procedure performed by Giles Peek MD, FRCS, CTh, FFICM, The Children’s Hospital at Montefiore, Bronx, NY.
