P0394 - Imaging Technique and Index of Suspicion Matter: Rare Vascular Ring

Introduction
The presence of a right-sided brachiocephalic artery that branches into right common carotid artery and right subclavian artery is commonly used in echocardiography to prove normal aortic arch anatomy and exclude a vascular ring. We report a rare vascular ring consisting of a double aortic arch with near atresia of the dorsal right aorta, which had the appearance of normal neck vessel configuration by echocardiography.

Case Description
An 8-month-old premature infant born at 25 weeks gestation remained admitted with bronchopulmonary dysplasia. She had been reintubated and required high positive pressure ventilatory support. Echocardiography demonstrated a left aortic arch with normal branching pattern. Non-contrast dynamic computed tomography (CT) of the airways demonstrated severe tracheal narrowing at the level of the arch, with superimposed excessive dynamic airway collapse. A CT angiogram to evaluate for vascular compression was sub-optimally timed, limiting diagnostic quality, but did demonstrate posterior course of the “right subclavian artery” at the level of airway narrowing, with mirror image neck vessel configuration at the thoracic inlet. Double aortic arch with atresia of the dorsal right arch was suspected. Because of the rarity of this entity, a repeat physician-supervised CT angiogram with optimized contrast timing confirmed the diagnosis of double aortic arch with near atresia of the dorsal right aorta, prior to surgical intervention. After the right arch was ligated and divided via posterolateral left thoracotomy, positive pressure ventilation was successfully discontinued.

Discussion
Branching of the right brachiocephalic artery is commonly used in echocardiography to confirm normal aortic arch anatomy. Typically, a coronal to axial sweep in the suprasternal notch reveals the first branch of the aorta coursing rightward and splitting into right common carotid artery and right subclavian artery. Left-dominant double aortic arches are rarer than right-dominant double aortic arches, and atresia of a double arch’s right dorsal segment is extremely rare. This anatomy can mimic the typical echocardiographic features of a left arch with normal branching. Because of the posterior course of the “right subclavian artery” in a double aortic arch with atretic right segment, an astute sonographer may note that the probe has to be rotated by 90 degrees to demonstrate branching. When the diagnosis remains in question, CT angiography remains the diagnostic gold standard.

Conclusion
Although double aortic arches are rarely left dominant, and atresia of the right arch is extremely rare, this case highlights the importance of maintaining a high index of suspicion in a patient with focal airway narrowing, a posterior course of the "right subclavian artery", and a mirror image pattern of the neck vessels at the thoracic inlet. A well-timed CT angiogram in this case allowed a more precise diagnosis and illustrates its utility in planning surgical intervention.