Laboratory Studies
- No laboratory screening or diagnostic study exists for this abnormality.
Imaging Studies
- Chest radiograph
- 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 and/or atelectasis of some of the lobes of either lung.
- A specific finding associated with 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 esophagram
- Most authorities consider barium esophagram to be the most important study in patients with a suspected vascular ring, and it is diagnostic in the vast majority of cases.
- 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 having 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 esophagram.
- Echocardiography and color-flow Doppler
- Echocardiographic studies have been increasingly used for the diagnosis of a vascular ring.
- This study has replaced pulmonary angiography at many centers to determine the presence of an anomalous left pulmonary artery. It is also extremely useful in the diagnostic workup of associated congenital cardiac defects.
- Some limitations in diagnosis using this study exist. 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 may be difficult to detect, especially for the less experienced echocardiographer.
- Computerized tomography scan, magnetic resonance imaging, and digital subtraction angiography[8]
- These expensive radiological studies are rarely necessary to evaluate vascular rings.
- Computerized tomography (CT) scan, 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 relationships to one another.
- Although these modalities provide excellent delineation of all of the associated structures, they should be reserved for cases in which the results of barium esophagram do not provide a clear diagnosis. MRI has been proposed as an excellent substitute for angiography.[9]
- All of these studies have drawbacks. CT scan and DSA expose the patient to radiation and require intravenous contrast. MRI requires patients to remain very still, so very young patients who are unable to understand verbal instructions require sedation. This may be particularly risky in young children with existing airway compromise. The expense encountered with these investigations must also be considered.
- Aortic angiography and cardiac catheterization
- In the past, diagnostic aortography was performed in selected cases to delineate the anomalous arch vasculature.
- It is generally agreed at present that, in the vast majority of cases, this study adds very little to the information obtained from a barium esophagram. If additional studies are required, echocardiography, CT scan, or MRI can usually provide the required information. However, reported cases exist of rare arch anomalies in which aortography was the only study from which the correct anatomic configuration was identified.[10] This study may be required in cases in which the diagnosis and arch configuration remains in question after other less invasive studies fail to provide a definitive answer.
- Cardiac catheterization is useful in cases in which associated cardiac abnormalities are known or suspected.
Diagnostic Procedures
- Bronchoscopy
- This diagnostic study has been used in the evaluation of children with symptoms of airway obstruction or compression. It is most commonly used in 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. Note that 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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