Asymmetric fusion of the artery bulbar and truncal ridges resulting in anterosuperior displacement of the outlet septum generates tetralogy of Fallot 2. The anterosuperior deviation of the outlet septum relative to the rest of the ventricular septum causes an anterior misalignment type of ventricular septal defect, pulmonary obstruction, overriding or dextroposition of the aorta, and right ventricular hypertrophy 7. In addition to the main features, TOF is associated with other structural abnormalities 3, such as a right aortic arch 5, a deviated cardiac axis, an aberrant subclavian artery, and an absent ductus arteriosus 7.
Pulmonary atresia (PA) type accounts for 30% of TOF cases. In pulmonary atresia, the subpulmonary artery is reperfused by the ductal arch or by the somatopulmonary collateral from the descending aorta. This case of TOF with PA featured a right aortic arch with left ductus arteriosus connected between the dilated left innominate artery and subpulmonary arteries. A recent study reported prenatal TOF detection rates of only 30–60% 1, and differentiation of TOF subtypes with unusual associated malformations is even more challenging 1,7. Ignorance of this potential connection between dilated left innominate artery and subpulmonary arteries via left ductus arteriosus can lead to misdiagnosed as absent ductus arteriosus.
In the current case, we suspected that the ductus arteriosus may exist but with abnormal connectivity based on detection of dilated subpulmonary arteries with reversed bidirectional blood flow. Furthermore, a right aortic arch with mirror image branching is usually associated with left ductus arteriosus connected to the descending aorta or the left innominate artery. Subsequently, we found that the dilated left innominate artery originated at the aorta arch, providing a rationale to scan the upper chest in the coronal plane to look for the linkage between dilated left innominate artery and subpulmonary arteries. Finally, the ductal arch connected between the dilated left innominate artery and subpulmonary arteries was detected, thus avoiding prenatal misdiagnosis as absent ductus arteriosus, and the pulse wave Doppler (PW) demonstrated the expected flow pattern. The correct structural assessment of the aortic arch, the branches of the aortic arch, ductus arteriosus, and pulmonary artery by prenatal ultrasound could aid in fetal prognosis of complex TOF 4.
According to the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) guidelines, a set of standard views plus additional views (the upper chest coronal view) are required for diagnosis of complex TOF. Complete acquisition of these standard views combined with careful analysis could reduce the risk of prenatal misdiagnosis and be useful for pregnancy counseling.