Unitat de Medicina Materno fetal (Diagnòstic Prenatal) Hospital de l"Esperit Sant. Santa Coloma de Gramanet, Spain.

Definition

"The left or right sidedness of the aortic arch refers to the position of the aortic arch relative to the trachea. It does not refer to which side of the midline the aorta ascends." [Yoo]

Incidence

Right-sided aortic arch is the most common arch anomaly in pediatric patients. It"s been suggested a 1 of 1000 pregnancy rate in a low risk population. The diagnosis has come more frequent since the position of the aortic arch is systematically included in the routine fetal exploration.

Embryological origin

The embryological origin consists of an abnormal development of the fourth branchial arch. Normally, the aortic arch is formed by the left fourth aortic arch and the left dorsal aorta. If the right dorsal aorta persists and the distal left aorta disappears, then we have a right aortic arch.

Sonographic findings

The three-vessel and trachea view is part of the routine exploration of the fetal heart. In the case of the right sided aortic arch, we don"t see the normal V shape configuration, because there is a gap between the ascending aorta and the mean pulmonary artery. The aortic arch is located to the right of the trachea instead of its normal left position.

Important remarks

Always look at the V shape configuration of the three vessel and trachea view. When we found a U image, then we must think of the right aortic arch.  The second thing we must look for is the trachea. Normally, it is located laterally to the aortic arch. In the case of the right sided aortic arch, it remains in the middle of the U, between the two great vessels.

Clinical forms

1. Right-sided aortic arch with aberrant right subclavian artery. In these cases, the right subclavian artery arises from the descending aorta and runs rightward behind the trachea and the esophagus. The confluence of the ductus and the right sided aortic arch behind the trachea and esophagus forms a U shaped image, typical for this clinical variety. The proximal part of the aberrant left subclavian artery that carries the blood from the ductus to the descending aorta during fetal life remains dilated as a diverticular pouch called the diverticulum of Kommerell. This segment becomes more apparent with the regression of the ductus arteriosus in the postnatal period.

2. Right-sided aortic arch with mirror image branching. In this case, the right sided aortic arch does not joint the ductus forming a V nor a U shaped confluence. This clinical form is more frequently associated with cardiac malformations, namely Tetralogy of Fallot (10-50%) or pulmonary atresia with ventricular septal defect (27%) - and abnormal karyotype (22q11 microdeletion and others).

Outcomes

It depends on the presence of associated anomalies. When isolated, the prognosis is good. In the cases of a mirror image branching, symptoms are unlikely to occur while in right sided aortic arch with aberrant left subclavia, is more frequent to find symptoms of compression of the trachea and esophagus (laryngeal stridor, cyanosis, respiratory distress, apnea, and/or a characteristic high-pitched, brassy cough, dysphagia lusoria). If there is a double aortic arch, surgical solution may be necessary.

Case report

A 23-year-old woman G2P1 first time presented at 19th week of pregnancy. Her first baby had a pulmonary stenosis. Ultrasound investigation revealed a hypoplastic thorax and decreased fetal movements. A single umbilical artery was also seen. We repeated the scan at 20th week and the fetus had normal movements but in the three vessel view, we saw an "U" image with trachea and esophagus in the middle. The initial diagnosis was of a right aortic arch. Amniocentesis was performed, 46, XX normal. The diagnosis was confirmed at birth and the baby is doing well.

References

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4. A. Sosa , L. Díaz , G. Giugni . Kommerell"s diverticulum  In www.thefetus.net/

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