Tetralogy of Fallot is the most common complex congenital heart disease comprising a dilated ascending aorta overriding a ventricular septal defect, pulmonary valvular and subvalvular stenosis and right ventricular hypertrophy. The anatomic landmark of the pathology is the anterocephalad deviation of the outlet septum that creates the mallalineament ventricular defect, the pulmonary stenosis and the overriding aorta.
There are many variants of the disease, including right aortic arch and pulmonary atresia. In the fetus the post-natal right ventricular hypertrophy is not yet present and the diagnosis is mostly based on the recognition by two-dimensional echocardiography of the overriding aorta and the unrestrictive subaortic ventricular septal defect.
The disproportion between the dimension of the ascending aorta and of the pulmonary trunk is also evident, especially in cases of pulmonary atresia and tends also to increase during pregnancy.
The pulmonary blood supply in case of pulmonary atresia is originating from the ductus arteriosus and/or systemic collaterals from thoracic aorta.
Figure legends
Pulmonary atresia with ventricular septal defect (extreme Fallot). Right aortic arch. Fetal heart of 21 wks of gestation.
Figure 1: External view: Hypoplastic Pulmonary trunk (PT). Dilatation of the ascending aorta and right aortic arch with mirror-image distribution of the epiaortic arteries.
Figure 2: section “4-chamber view” like: The dextroposed aorta (AO) overrides the ventricular septal defect (VSD)