Subclavian Steal Phenomenon Associated With Vascular Ring in an Infant Who Had a Prenatally Diagnosed Right Aortic Arch With an Atretic Aberrant Left Subclavian Artery

A full-term female fetus prenatally diagnosed with RAA by using perinatal ultrasound was referred to our pediatric cardiology clinic for further evaluation. An echocardiogram at birth showed a small muscular ventricular septal defect (VSD) and an RAA with a retroesophageal left subclavian artery, forming a substrate for a vascular ring. The atretic part of the aberrant subclavian artery could not be visualized on a Doppler echocardiogram. Because the patient was asymptomatic, she was monitored clinically for several months without intervention. At 7 months of age, the patient was noted to have noisy breathing but showed no other cardiac symptoms and had been growing and developing appropriately. Further evaluation with cardiac MRI using gadoterate meglumine contrast (0.2 mL/kg of body weight) showed an RAA with an aberrant origin of the left subclavian artery, forming a vascular ring. A Kommerell diverticulum on the left side of the anterosuperior aspect of aorta gave rise to the ALS. A short segment of the left subclavian artery was not opacified when contrast was reconstituted at the level of the left vertebral artery (Fig. 1). The distal portion of the left subclavian artery seemed to be filled from retrograde flow in the left vertebral artery, raising concern for subclavian steal phenomenon. No significant narrowing of the airway was observed at the level of the vascular ring.

We describe a case of RAA-ALS in which an atretic left subclavian artery was associated with collateral retrograde flow from the left vertebral artery to the distal portion of subclavian artery. The patient was diagnosed prenatally and referred to our clinic for evaluation after birth. In this case, an echocardiogram was sufficient to diagnose RAA-ALS, but atresia of the ALS could not be detected.

The presentation of a vascular ring varies from incidental findings on imaging to severe respiratory distress or feeding difficulty. The 2 most common types of vascular ring are double aortic arch (DAA) and RAAALS with a left patent ductus arteriosus or ligamentum arteriosum.¹  A retrospective review of vascular ring diagnosed from 1974 to 2000 revealed that 38% of cases were DAA, whereas 27% were RAA-ALS.³  However, in recent years, the prevalence of each type of a vascular ring has changed because of improved diagnostic imaging techniques. A more recent retrospective review of vascular ring diagnosed from 1990 to 2015 revealed that 77% of cases were RAA-ALS, whereas only 20% of cases were DAA.²  Evans et al suggested that RAA-ALS may be more prevalent than is DAA in asymptomatic patients, who may not have been previously diagnosed.²  Vascular ring associated with RAA-ALS is relatively loose and generally asymptomatic or mildly symptomatic.

Subclavian steal is a phenomenon in which subclavian artery occlusion or stenosis proximal to the origin of the vertebral artery results in the reversal of flow in the ipsilateral vertebral artery and a steal of blood from the brain.⁴  Subclavian artery occlusion or stenosis proximal to the origin of the vertebral artery typically causes reduced pressure in the distal subclavian artery. Consequently, blood flows from the contralateral vertebral artery to the basilar artery and may flow in a retrograde direction down the ipsilateral vertebral artery, away from the brainstem.⁵  Atherosclerosis is the most common cause of subclavian artery stenosis. Other conditions, such as Takayasu arteritis, surgical repair of coarctation of the aorta or tetralogy of Fallot, and RAA with isolation of the left subclavian artery, can also cause subclavian artery stenosis or occlusion.⁶ 

To date, 9 cases of subclavian steal phenomenon associated with RAA-ALS have been reported. In 5 of those cases, the patients were less than 18 years of age, which included 2 neonates or infants (Table I).^7–12  In both of those cases, the patients presented with respiratory symptoms, and a cardiac angiogram incidentally showed subclavian steal phenomenon. Neither patient had neurological symptoms at presentation.^7,11  The present case is the third of such reported to date in an infant and is the first in which no heart defect was present and MRI was used for the diagnosis. In a similar case, Powell et al described a case of RAA-ALS with subclavian steal phenomenon in an 8-year-old girl.¹⁰  Most other cases in children have been associated with other congenital heart diseases such as VSD and tetralogy of Fallot.^7,10,11  In those cases, the patients presented to the hospital with symptoms related to the type of congenital heart disease and were found to have RAAALS. A few cases have been reported of subclavian steal syndrome associated with an RAA and an atretic ALS developing in adults who are in their 50s and 60s.^7–9  Adult patients present more often than do pediatric patients with neurologic symptoms related to subclavian steal syndrome.^7–9,12  One adult case of RAA-ALS has been described that was diagnosed on the basis of an abnormal chest x-ray.¹² 

In the present case, MRI was used to identify the interruption of the left proximal subclavian artery that was associated with collateral retrograde flow from the left vertebral artery to the distal portion of the subclavian artery. Although congenital arterial atresia is often associated with collateral formation, collaterals were not identified in this patient. Because of the patient's age, it was difficult to assess whether the blood flow was inadequate to meet the metabolic and functional needs of the vertebral system. We speculate that treating RAAALS with an atretic subclavian artery may prevent the typical subsequent worsening over time resulting from overriding atherosclerosis.

In conclusion, we believe this case report helps increase the awareness of subclavian steal phenomenon in patients with anatomic variance and demonstrates the utility of MRI or CT scans in such cases. Imaging studies are seldom performed in children with absent or mild symptoms or who do not have other congenital heart diseases. However, MRI with contrast without radiation exposure is a safe option¹³  and may be considered for detecting subclavian steal phenomenon. As children with this condition grow older, the risk of developing progressive subclavian steal phenomenon may increase. In addition, surgical repair may be beneficial for preventing future neurologic complications. Thus, we recommend that MRI or CT should be considered for patients who have a vascular ring resulting from RAA-ALS, even if symptoms are absent or mild.