Transitional AV Canal (aka atrioventricular septal defect with a common AV junction with shunting at the atrial level and restrictive ventricular level shunting)
The term transitional AV canal most commonly refers to the combination of an atrial septal defect (primum ASD), and a small restrictive inlet ventricular septal defect, which is often mostly occluded by accessory AV valve tissue. A single valvar annulus is usually present where the anterior and posterior bridging leaflets fuse overlying the ventricular septum.
Fetal Imaging Pearls
Four-chamber view diagnostic will demonstrate presence of a primum ASD and small restrictive VSD
Assess common AV valve function for worsening regurgitation or stenosis
If unbalanced transitional AV canal variant, assess interval growth of ventricles, semilunar valves, great arteries and ductal and aortic arches to determine if lesion is ductal dependent
Rarely required unless unbalanced variant which may require PGE for ductal dependent systemic or pulmonary blood flow