The prenatal detection of a right-sided aortic arch achieved mainly by targeted visualization of the three-vessel and three vessels and trachea (3VT) view, with or without color Doppler, has been discussed recently in this journal1–4.
Two typical forms of a right aortic arch can be distinguished5, 6. In one condition a vascular ring is found around the trachea, the so-called U-sign prenatally (Figure 1)2, 3. The trachea and esophagus are entrapped between the right aortic arch and the left ductus arteriosus and this abnormality is often an isolated incidental finding prenatally2. In the other condition, both the aorta and ductus arteriosus lie to the right of the trachea without a vascular ring. This condition is very commonly associated with cardiac anomalies5.
The branching pattern of the great vessels arising from the aortic arch in both conditions is of major interest in pediatric cardiology5, 6. The right aortic arch without a vascular ring usually exhibits mirror image branching of the arteries with the left innominate (brachiocephalic) artery arising first followed by the right common carotid and right subclavian artery6. By contrast, the right aortic arch with vascular ring very often has an association with an aberrant left subclavian artery. The left common carotid arises first from the aortic arch, followed by the right common carotid, right subclavian artery, and finally a retroesophageal vessel segment from which the left subclavian artery arises and the ductus arteriosus connects. The retroesophageal (and retrotracheal) vessel segment is known as the diverticulum of Kommerell. In other words, the left subclavian artery is connected ventrally to the ductus arteriosus arising from the left pulmonary artery, and dorsally through the Kommerell's diverticulum to the descending aorta. In postnatal life, after closure of the ductus arteriosus, blood enters the left subclavian artery via the descending aorta and Kommerell's diverticulum4.
Prenatal assessment of a right-sided aortic arch and its branching pattern requires scanning in such planes as a transverse 3VT view (Figure 1), oblique cephalad planes and coronal longitudinal views ventrally from the spine. In the latter planes, the aortic arch lies to the right of the trachea, and the connection with the diverticulum of Kommerell is recognized as a Y-shaped structure dorsal to the trachea (Figure 2)2, 4. The cephalic vessels arising from the aortic arch can be visualized in more ventral planes, but because of their horizontal course the use of power Doppler ultrasound, which is superior to color Doppler in such insonation conditions, is advised.
The Picture of the Month demonstrates a prenatal three-dimensional power Doppler ultrasound (3D-PDU) rendering of a right aortic arch with a vascular ring (around the trachea and esophagus) and the associated aberrant left subclavian artery (Figure 3).
The patient was referred at 23 weeks' gestation because of an abnormal 3VT view. No additional cardiac or extracardiac anomalies were found. Abnormal chromosomes including microdeletion 22q11 were excluded by amniocentesis. The aberrant left subclavian artery was diagnosed by color and power Doppler. 3D-PDU rendering was performed at 35 weeks using commercially available equipment (Voluson 730 Expert, Kretztechnik, Zipf, Austria) with a 4–8-MHz transducer and 3D-static mode combined with power Doppler ultrasound. The examination was performed from the fetal left side after the left aberrant subclavian artery was visualized on two-dimensional power Doppler (Figure 2a).
3D-PDU has been shown to be useful in fetal vascular malformations, but its application for the fetal heart is still considered limited due to lack of cardiac cycle triggering7. In a previous issue of this journal we demonstrated the crossing of the great vessels in a normal human fetus using 3D-PDU, explaining how to obtain clear signals without heart rate gating8. The example presented with this case emphasizes the possible clinical usefulness of 3D-PDU, in facilitation of the spatial orientation of the aortic arch, pulmonary artery with ductus arteriosus and Kommerell's diverticulum, as well as the demonstration of the origin of the cephalic vessels (Figure 3). Unfortunately, clear demonstration of all cephalic vessels arising from the aortic arch was not possible, the limiting factors being chiefly ribs shadowing as well as the overlapping from neighboring veins when the low-velocities preset is chosen. The trachea and esophagus are not seen on the 3D image but the reader can imagine them within the ring formed by the aortic arch on the right and the ductus arteriosus and diverticulum of Kommerell on the left.
The 3D image was presented to the pediatric cardiologists and neonatologists at our institution and they found the image to be comparable with postnatal 3D images acquired by spiral computed tomography2, 4. Follow-up after birth was decided upon.
Spontaneous birth occurred at 39 weeks, and echocardiography as well as angiography (Figure 4) confirmed the diagnosis with no additional anomalies. At 6 months of age, no complications were observed, and cardiological and clinical follow-up are planned.
Occasionally, this anomaly may present either with stridor or dysphagia due to the compression of the trachea9 or esophagus10. Left subclavian steal syndrome due to constriction of the aberrant artery may also occur11. Achiron et al.2 reported that only 1/18 children with right aortic arch was symptomatic first at the age of 6 months. In a similar case seen recently at our institution, constriction of an aberrant left subclavian artery occurred at 10 days of age, necessitating catheter dilatation and stent insertion.
In summary, 3D-PDU can be utilized in fetal cardiology even without cardiac cycle triggering. The new method provides the clinician with information similar to that of postnatal angiography and facilitates the spatial understanding of the anomaly. Future work will show which further cardiac anomalies are amenable to 3D-PDU rendering.