Volume 6, Case 19
Loren G. Yamamoto, MD, MPH
Kapiolani Medical Center For Women And Children
University of Hawaii John A. Burns School of Medicine
This is a 6-month old male who presents to the pediatric clinic with difficulty breathing. He has had similar episodes in the past. He has been diagnosed with asthma and has been treated with albuterol with only modest improvement. He has some nasal congestion, but no fever, vomiting or diarrhea. He feeds well and he has been gaining weight well.
His past history is remarkable for multiple upper respiratory infections and wheezing during the past several months. He was born at term. His family history is significant for asthma in several relatives and his older siblings. He has three siblings who currently have colds.
Exam: VS T 37, P 114, R 39, BP 100/75, oxygen saturation 99% in room air. He is alert, active, and in no distress. He is not toxic. HEENT significant for clear nasal mucus, normal TM's and a clear pharynx with normal oral mucosa. Heart regular without murmurs, but his breath sounds are noisy so it is difficult to be sure. He has mild inspiratory and expiratory "wheezing". His lung fields demonstrate good aeration. He has no retractions. His abdomen is soft, non-tender and without organomegaly. His neurologic exam is unremarkable.
An albuterol aerosol is administered and following this, his lung exam is unchanged. A chest radiograph is ordered. An airway anomaly is also suspected so a lateral neck is also ordered.
View CXR PA view.
Lateral view.
View lateral neck.
This is a 6-month old child with a history of several episodes of dyspnea, noisy breathing and/or wheezing. A chest or airway anomaly of some sort is suspected. Take a minute to review these carefully.
The PA view of the chest is unremarkable although a right sided aorta can be suspected here. The lateral view of the chest demonstrates a very narrow tracheal air column which is also bent suggesting extrinsic compression of the trachea. The lateral neck is unremarkable.
View esophagram.
This esophagram demonstrates extrinsic compression of the esophagus consistent with a vascular ring.
Discussion
A vascular ring is a malformation of the aortic arch that results in vascular branches or major blood vessels encircling the trachea and esophagus. In nearly all instances, a right-sided aortic arch is present. In a double aortic arch (one of the most common vascular ring malformation patterns), the two arches encircle the trachea and esophagus.
See figure 1 - Double aortic arch.
In other vascular ring malformations, vascular remnants such as the ligamentum arteriosum (formerly the ductus arteriosus) may be part of the ring encircling the trachea and esophagus. In our patient's case here, further studies delineate a right sided aortic arch with an anomalous left subclavian artery, in which the ring is completed with a left sided ductus arteriosus which closes to become the ligamentum arteriosum.
See figure 2 - Right sided aorta with anomalous left subclavian artery.
Compare figures 1 and 2 to the normal anatomy of the aorta in its relationship to the trachea and esophagus.
See normal aorta.
Note that the normal aortic arch crosses over the left mainstem bronchus. This is the normal left sided aortic arch. In the vascular ring malformations diagrammed in figures 1 and 2, note that the aortic arch passes over the right mainstem bronchus instead. This is an abnormal right sided aortic arch. In figure 1 (the double aortic arch), the aortic arch bifurcates such that one half of the aorta crosses over the left mainstem bronchus, while the other half of the aorta crosses over the right mainstem bronchus. In figure 2 (the right sided aorta with anomalous left subclavian), the aortic arch crosses only over the right mainstem bronchus.
Review figures 1 and 2 again.
Recognition of the right sided aortic arch is often a valuable clinical clue in suspecting a vascular ring.
A vascular sling (as opposed to a vascular ring) is said to be present when the vessels form an incomplete circle around the trachea and esophagus.
Children with vascular rings are often diagnosed during infancy, but presentations later in life my occur in more mild cases and many cases are totally asymptomatic. Presenting symptoms are usually due to tracheal or esophageal compression such as stridor, noisy breathing, frequent respiratory infections, wheezing, dysphagia, choking, apnea, wheezing, croupy cough, hoarse cry, etc. A typical presenting history is that of noisy breathing since birth. It is common for these infants to have more severe symptoms during a respiratory infection. A young infant with a history of "asthma" is another typical way that these patients present. Sometimes these children are diagnosed with cardiac disease, but the vascular ring may be occult until an appropriate imaging study is performed.
The key in making the diagnosis is to suspect an airway problem based on symptoms described by the parents. Clinical findings may or may not be present during an examination. Two view chest radiographs are useful in identifying many pulmonary and cardiac anomalies, but the findings are often subtle. Since a right sided aortic arch is almost always present in a vascular ring, identifying this on a chest radiograph is critical. A right sided aortic arch is defined as an aortic arch that crosses over the right mainstem bronchus instead of the usual left mainstem bronchus. Thus, the arch itself may not necessarily occupy the right hemithorax. The normal left sided aortic arch normally pushes the carina to the right as it courses over the left mainstem bronchus. This slight deviation in the normal tracheal air shadow can often be appreciated on the AP or PA view of the chest radiograph. In a right sided aortic arch, the carina deviates to the left instead as the aorta courses over the right mainstem bronchus.
See figure 3.
The diagram on the left illustrates the rightward deviation of the distal trachea which occurs when the normal left sided aorta crosses over the left mainstem bronchus. The diagram on the right illustrates the left sided deviation of the distal trachea which occurs when the right sided aorta crosses over the right mainstem bronchus.
In a double aortic arch, leftward deviation of the carina may not be visible on the chest radiograph because both left and right aortic arches are present. However, since a double aortic arch often forms a large caliber ring, tracheal compression is often visible on the lateral view of the chest radiograph. In cases where no carina deviation is present and the side of the aorta cannot be determined, a double aortic arch should be suspected.
The lateral view of the chest radiograph may reveal a narrowed or constricted tracheal air column (as was seen in the patient in this case). Once an airway anomaly or right sided aortic arch is suspected on plain chest radiographs, a more advanced imaging study should be performed to delineate the anatomy definitively.
Occasionally, bronchial compression is severe and unilateral hyperinflation can be seen on the AP or PA view of the chest radiograph. This usually suggests a pulmonary artery sling, a bronchial anomaly or compression of the bronchus by some other structure.
An esophagram (barium swallow) is helpful in making the diagnosis and historically, the esophagram was heavily relied upon to delineate the malformation until angiography was performed. Currently, advanced imaging methods such as echocardiography, CT scanning, magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) may eliminate the need for esophagrams, since they are non-invasive and they define the anatomy of the malformation well.
Treatment focuses on the surgical correction of the malformation with the goal of relieving the patient's symptoms.
References