SPR Unknown #62 -- FINAL
SPR Unknown 62
Publication Date: 2011-12-07
3 year old male
Figures 3-8: Consecutive axial slices from CT angiography of the chest demonstrate a right aortic arch with three vessels branching from the arch. A small common carotid trunk that immediately bifurcates into the left common carotid and right common carotid artery, right subclavian artery, and aberrant left subclavian artery that courses posterior to the esophagus.
1. Other types of vascular ring (double aortic arch, etc.).
2. Mass displacing the trachea.
A vascular ring occurs when abnormal embryonic development of the aortic arch system leads to encirclement of the trachea and esophagus by vascular or ligamentous structures . In normal embryonic development there are initially six pairs of aortic arches, some of which become the carotid, subclavian and pulmonary arteries, ductus arteriosus and normal left aortic arch, while the remainder of the arch pairs regress . However, persistence or abnormal regression of the arch pairs can lead to the development of a variety of aortic arch malformations, some of which form complete vascular rings.
One of the most widely accepted classification systems groups these anomalies primarily based on the side of the aortic arch, the aortic branching pattern and the location and course of the ductus . Vascular rings are initially grouped based on the presence of either double aortic arches, a left aortic arch or a right aortic arch. Subtypes among the double aortic arch group are further divided based on whether or not both arches are patent or if there is atresia of one of the arches. Vascular rings involving a left aortic arch are complete if there is a right ductus arteriosus, which is rare since the ductus arteriosus and ligamentum arteriosum are normally left-sided structures. More commonly, a right aortic arch with an aberrant left subclavian artery forms a vascular ring when a left ligamentum arteriosum connects the left subclavian artery to the pulmonary artery. Other rings associated with a right aortic arch involve either mirror-image branching, circumflex aorta or a right cervical aortic arch.
Although there are a variety of different types of vascular rings, as a whole, they account for less than 1% of congenital cardiovascular defects . Over 90% of the cases are either double aortic arches or a right aortic arch with left ligamentum arteriosum . Depending on the degree of constriction, patients may or may not be symptomatic. If present, symptoms most commonly manifest in infancy or early childhood and may include stridor, respiratory distress, recurrent pneumonia, apnea, dysphagia, recurrent vomiting and failure to thrive . Of the different types of vascular rings, double aortic arches typically produce the most severe symptoms as they are usually the most constrictive .
Several important imaging findings should be considered in the evaluation of potential vascular rings. In fact, one should look for these findings on all relevant pediatric exams because many cases of vascular rings are either asymptomatic or the symptoms are very nonspecific. On an anteroposterior radiograph, the presence or absence of tracheal deviation is a major clue as to whether the aortic arch is on the right, left or bilateral. Tracheal narrowing at the level of a right-sided aortic arch may be seen on the lateral radiograph and is highly suggestive of the presence of a ring . A barium esophagram is another examination that may indirectly be used to image vascular rings and the impressions they make on adjacent structures. If an aortic arch abnormality with compression of the trachea and/or esophagus is suspected on the barium esophagram, further investigation with cross-sectional imaging is needed for definitive diagnosis and treatment planning as surgical intervention is required in cases of true vascular rings that are symptomatic. It is important to note that the lack of tracheal compression or distortion implies that either a complete ring is not present or the ring does not require surgical treatment .
While sonography and angiography have certain limited advantages in the assessment of vascular rings, MRI and CT are preferable for detailed diagnostic and preoperative evaluation . The surgical approach typically depends on the side of the dominant aortic arch, which means that accurate identification of anatomic variants, via CT or MRI, is an important part of the preoperative assessment of these patients. Unfortunately, these modalities are unlikely to reveal the small ligamentous or atretic segments that complete some rings, which forces the interpreter to rely on identification of the vascular branching pattern, the side of the aortic arch or arches and narrowing of the airway to make the diagnosis in these cases .
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