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Fascinating Fetal Finds: Fall 2014

A patient was referred to The Fetal Center at Children’s Memorial Hermann Hospital for a fetal echocardiogram because of a maternal history of mitral valve prolapse in addition to a family member born with congenital heart disease who died as an infant. The echo confirmed normal abdominal situs and cardiac connections but scanning at the level of the three vessel and tracheal view demonstrated a right-sided aortic arch with an aberrant left subclavian artery and a left-sided arterial duct.

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Echo One: The vascular ring is formed by the right-sided aortic arch (RAA) and left-sided ductal arch surrounding the trachea (T). The pulmonary valve (PV), superior vena cava (SVC), and spine (SP) are also identified and used as reference points.
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Echo Two: Shown with the aid of color doppler, the internal mammary vessels (IM) at the level of the brachiocephalic vein (BCV) delineating the fetal thymus. This is known as the “thy-box.”

These images show the vascular ring formed by the right-sided aortic arch (RAA) and left-sided ductal arch surrounding the trachea (T). There was no prenatal compression of either the trachea or esophagus. We identified the internal mammary vessels (IM) at the level of the brachiocephalic vein (BCV) delineating the fetal thymus. This is known as the “thy-box.”

A right-sided aortic arch (RAA) occurs when part of the embryological left arch regresses leaving the right fourth arch or right dorsal aorta. It can be a normal variant and may occur in isolation. More commonly it is associated with cardiac malformations such as tetralogy of Fallot. The most common chromosomal abnormality associated with a right-sided aortic arch is 22q11.2 deletion, or Di George syndrome, reported in 8 percent of fetuses with isolated RAA. The thymus may be small in these babies and thus the demonstration of the ‘thy-box’ and a normal-sized thymus may lower the risk of a genetic etiology.

Normally both the aortic and ductal arches lie to the left of the trachea. When the ductus arteriosus closes a few days after delivery it leaves a fibrous cord behind. Usually this does not cause any problems; however, when the aortic arch and ductal arch are on different sides of the trachea and esophagus, as in this case, the fibrous cord may cause compression of the trachea and esophagus, resulting in the development of symptoms such as noisy breathing or difficulty swallowing. This can be difficult to diagnose and sometimes is not recognized until a child has had difficulty swallowing solids for several years. In addition, compression may be caused by an aberrant left subclavian artery arising from the descending aorta coursing behind the trachea and esophagus. This is most commonly associated with an isolated RAA and normal cardiac anatomy.

The newborn was clinically stable after delivery without any acute events including stridor or respiratory distress or any feeding issues. A repeat echocardiogram after birth confirmed the prenatal diagnosis and a cardiac MRI was performed when she was 4 days old and confirmed there was a right-sided aortic arch with a four-vessel branching pattern including an aberrant left subclavian artery. The aberrant left subclavian artery arose from the distal arch, coursing posterior to the esophagus and trachea, with mild narrowing of the trachea just above the carina. There was a diverticulum of Kommerell and thyromegaly without a focal lesion. The baby was discharged home and remains well at follow-up at 9 months. The parents understand that surgical intervention may be required in the future if she starts to develop symptoms of tracheal or esophageal compression.

The Fetal Center at Children’s Memorial Hermann Hospital, through the Congenital Heart Defect Screening Program, is advocating and training physicians and sonographers to routinely evaluate the three vessel and tracheal view as part of the second trimester anatomy review. This will allow for improved identification of fetuses at risk for developing a vascular ring. Prenatally we counsel parents and pediatricians about the risks associated with a vascular ring, thus avoiding a delay in diagnosis and associated morbidity for the child. The diagnosis of a vascular ring is best confirmed after delivery by MRI and most children will become symptomatic and require surveillance.

At Children’s Memorial Hermann Hospital, Michael Hines, M.D., professor of pediatric cardiovascular surgery at McGovern Medical School at UTHealth, performs thoracoscopic division of the vascular ring for patients requiring surgical intervention. This minimally invasive approach releases the tracheal and/or esophageal compression and avoids the need for more complicated surgery. The benefits are immediately obvious to the family.

Learn more

Visit childrensmemorialhermann.org/thefetalcenter for more information or to request a second opinion.