Introduction

We present the clinical course, echocardiographic, and genetic findings of two fetuses with an unusual vascular ring, created by a left aortic arch with a right-sided arterial duct and an aberrant right subclavian artery. Both cases were referred to our unit following identification of an abnormal three-vessel and tracheal view (3VT) on routine screening but otherwise normal first trimester screening and no extracardiac anomalies were reported on ultrasound.

Case 1

Fetal echocardiography at 19 + 6 weeks of gestation (Fig. 1) demonstrated a normally positioned aortic arch passing to the left of the trachea. However, the arterial duct passed to the right of the trachea (right-sided arterial duct). The origin of the right subclavian artery was retro-tracheal (aberrant). Fetal microarray-based comparative genomic hybridization (array CGH) was normal. Fetal cardiac magnetic resonance imaging (MRI) using motion correction techniques [1] at 30 weeks (Fig. 2) confirmed the ultrasound diagnosis. Postnatal echocardiogram at 8 days of age demonstrated the left arch and as expected, the arterial duct had spontaneously closed. At 2 months of age the baby was noted to have stridor while feeding (milk). A computerized tomography (CT) and flexible bronchoscopy showed no significant obstruction of the trachea. Swallow assessment showed pharyngeal dysphagia and aspiration on fluids, a specialist esophageal assessment is awaited.

Fig. 1
figure 1

Fetal echocardiogram performed at 19 + 6 weeks of gestation. The 3VT demonstrates the arterial duct passing to the right of the trachea (a, c) and on a more caudal view, the aortic arch passing to the left of the trachea (b) forming the vascular ring. Color Doppler shows the origin of the right subclavian artery (d) which is retro-tracheal (aberrant). LSA left subclavian artery, ARSA aberrant right subclavian artery, T trachea, * aorta, desc.Ao descending aorta, art.duct arterial duct, Ao arch aortic arch, Pa pulmonary artery

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Fig. 2
figure 2

Fetal cardiac MRI performed at 30 + 3 weeks of gestation. 3D segmentation of motion-corrected black blood volume, superior view, showing the normal left-sided aortic arch a right-sided arterial duct and aberrant right subclavian artery. AD arterial duct, ARSA aberrant right subclavian artery, LAA left aortic arch, LCA left carotid artery, LSA left subclavian artery, RCA right carotid artery, SVC superior vena cava, T trachea

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Case 2

Fetal echocardiography at 22 + 4 weeks of gestation demonstrated similar vascular anatomy as Case 1 (Fig. 3). The descending aorta was on the right of the spine in the upper mediastinum and the distal transverse aortic arch appeared slender as it passed behind the trachea, leading to a low suspicion of coarctation of the aorta (COA). In addition, a perimembranous ventricular septal defect (VSD) was present, spiral origin of the branch pulmonary arteries were noted and thymic tissue was not evident. Prenatal genetic testing was offered, but declined. Fetal cardiac MRI was undertaken at 31 weeks of gestation to provide an adjunctive assessment for COA. This confirmed the anatomy of the vascular ring, spiral origins of the branch pulmonary arteries, and absent thymus; with no additional extracardiac findings. 3D imaging of the distal aortic arch demonstrated an unusual oblique course as it passed behind the trachea to join the right-sided descending aorta (Fig. 4), however, the risk of early postnatal coarctation was felt to be low. Day 1 echocardiography confirmed the prenatal findings and the arterial duct was allowed to close with regular echocardiographic surveillance for COA. Genetic testing (array CGH) was undertaken confirming 22q11.21 microdeletion syndrome. A postnatal CT was undertaken on day 5 due to suspicion of left pulmonary artery origin constriction with ductal closure, but this was excluded as was neonatal COA. The infant remains asymptomatic at age of 3 months and continues to be under surveillance.

Fig. 3
figure 3

Fetal echocardiogram performed at 32 weeks of gestation. The 3VT demonstrates the arterial duct passing to the right of the trachea (a) and on a more caudal view, the aortic arch passing to the left of the trachea (b) forming the vascular ring. * aorta, desc.Ao descending aorta, art.duct arterial duct, Ao arch aortic arch, LPA left pulmonary artery, Pa pulmonary artery, T trachea

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Fig. 4
figure 4

Fetal cardiac MRI performed at 31 + 0 weeks of gestation. 3D segmentation of motion-corrected black blood volume, superior view (a), showing the normal left-sided aortic arch, a right-sided arterial duct and aberrant right subclavian artery. Unusual oblique course of the left aortic arch which crosses behind the trachea to meet right-sided proximal descending aorta (b). * aorta, AD arterial duct, ARSA aberrant right subclavian artery, LAA left aortic arch, LPA left pulmonary artery, LCA left carotid artery, LSA left subclavian artery, RPA right pulmonary artery, RCA right carotid artery, SVC superior vena cava, T trachea

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Discussion

A vascular ring is a relatively common congenital vascular anomaly usually formed by either a double aortic arch or the combination of a right aortic arch and left-sided arterial ductal ligament [2]. The combined position of the arteries ± ligaments encircle the trachea and the esophagus and can cause compression of these structures leading to symptoms after birth such as stridor, recurrent respiratory tract infections, and choking [2,3,4]. The term vascular ring was used by thoracic surgeon Robert Gross in 1945 who reported the first experiences of successful surgical division of vascular rings [5] caused by a double aortic arch or a right arch with left ductal ligament. In the current era, the most common mode of diagnosis of vascular rings is with fetal echocardiography. These can be appreciated by the formation of a “U” or “Z” configuration in the upper mediastinum rather than the expected “V” [6]. However, to our knowledge, this type of vascular ring formed by a left aortic arch and right arterial duct with aberrant right subclavian artery has not been demonstrated previously in the fetus. Due to the origin of the arterial duct from the pulmonary artery and then passing to the right of the trachea, it does not form the typical “U” as might be expected.

Prenatal diagnosis of the first case facilitated surveillance and made it possible for the parents to seek advice when the infants became symptomatic. This infant presented unusually early with stridor while being only milk-fed and subsequently struggled with weaning onto solids. In our experience, it is unusual for a 2-month old with a vascular ring to present with feeding-related symptoms [7] and, from our institutional experience, also unusual for an isolated aberrant right subclavian artery to present with early symptoms [8]. Without prenatal diagnosis the vascular ring would have gone unnoticed due to closure of the arterial duct which occurs with transition to the postnatal circulation. The second case demonstrated soft markers for an underlying genetic condition—perimembranous VSD, spiral origin of the branch pulmonary arteries, and an aberrant right subclavian artery. In combination, with the absence of the thymus, there was a strong suspicion of 22q11.2 microdeletion such that counseling for genetic syndromes could take place. Although the parents chose not to undertake prenatal testing, they were prepared for the postnatal diagnosis.

In our institution, fetal cardiac MRI is used as an adjunct investigation to fetal echocardiography where there is a vascular abnormality found on ultrasound to greater appreciate the 3D relationships between the cardiac structures.

Hence, with the three-vessel view being a standard view during routine fetal echocardiography, rare forms of vascular ring may be recognized. This type of vascular ring is rare [9] and has not been described in the fetus. In children with symptoms or signs of tracheoesophageal compression in the presence of a left aortic arch, the presence of a vascular ring which is completed by a right-sided arterial ductal ligament may be under-recognized as differential diagnosis.