- Prenatal diagnosis of truncus arteriosus with two-dimensional sonography requires expertise in fetal echocardiography. Indeed, truncus arteriosus shares with tetralogy of Fallot and pulmonary atresia with a ventricular septal defect (VSD) the sonographic finding of a single arterial trunk overriding a VSD. The diagnosis of truncus arteriosus can be confirmed when either the main pulmonary artery or its branches are visualized arising from the truncus itself. This requires sequential examination of multiple scanning planes and a process of mental reconstruction of their spatial relationships. The advantage of multiplanar imaging in three-dimensional and four-dimensional ultrasonography is that it allows for the simultaneous visualization of three orthogonal anatomic planes, which can be very important in diagnosing cardiac abnormalities. We report, first, a case of truncus arteriosus diagnosed in utero where the multiplanar display modality provided important insight into the differential diagnosis of this conotruncal anomaly, and then, review the diagnosis of truncus arteriosus on ultrasound.