1357021 - How Much Is Stolen? – Now That Is The Question! - Ductal Origin Of The Right Subclavian Artery With Significant Pulmonary Steal.

A 3 year-old boy presented with stridor and nasal regurgitation since infancy. A cluster of clinical findings including cleft palate and speech delay raised the suspicion of velocardiofacial syndrome. Genetic testing confirmed 22q11 deletion. In light of the new diagnosis, clinical assessment and imaging of the cardio-vascular system was performed to evaluate the known association of conotruncal and aortic arch abnormalities. The child was asymptomatic with respect to the cardiovascular system at the time of presentation.
 

 

 

 

Diagnostic Techniques and Their Most Important Findings:  

Initial echocardiogram revealed situs solitus with normal segmental and outflow tract anatomy. The aortic arch was left sided and unobstructed. There was variant branch anatomy with suspected ductal origin of the right subclavian artery showing reversal of flow on Doppler.

Cardiac magnetic resonance imaging (CMR) was performed to confirm these findings and evaluate the physiologic effect of the lesion. 3D MR angiogram confirmed the ductal origin of the right subclavian artery. Focal proximal stenosis of the aberrant vessel was noted with a 90-degree kink along it’s mediastinal course (fig 1). Phase contrast imaging demonstrated pulmonary steal with complete reversal of flow in the right ductus arteriosus. Steal was primarily from the right vertebral artery along with multiple additional sources including the right subclavian artery (with collateral supply from the right lateral thoracic artery), a dilated right internal mammary artery, and thoracic aortic branches (fig 2). 

CMR demonstrated retrograde flow in the ductus, approximately 2.2 L/min/m2. This was 36% of total pulmonary blood flow / left ventricular cardiac output. The left to right shunt resulted in Qp:Qs of 1.6:1. The volume overloaded left ventricle was dilated with LVEDVi of 127 ml/m2 (Z-Score = +6.52),  ejection fraction was preserved (fig 3).
 

 

 

 

Learning Points from this Case:  

Isolated anomalies of the right subclavian artery including ductal origin, are documented anatomical markers of monosomy 22q11(1,2). Clinical presentation may include evidence of limb ischemia, increased pulmonary blood flow and vertebro-basilar insufficiency.

When symptomatic or, as in our case, when shunting overloads the heart, percutaneous closure/surgical ligation of the vessel with reimplanation into the aorta or common carotid artery are treatment options(3). From our institution experience, it is prudent to perform a pre-operative cerebral venous occlusion study, to preempt adverse cerebral hemodynamics after shunt closure.

CMR is invaluable in delineating this rare anomaly. Large field of view enables complete assessment of contributing collaterals in large shunts, information vital to the surgeon. Beyond the capability of other imaging, CMR identifies the hemodynamic significance with reliable quantification of the pulmonary steal. CMR simultaneously evaluates shunt related volume overload and ventricular function (4). This enables the treating team to plan preventive management prior to overt symptom manifestation.