Prenatal visualization of persistent 5th aortic arch artery.

The embryonic arches develop in the fourth and fifth gestational weeks with the corresponding pharyngeal arch arteries connecting the aortic sac with the dorsal aorta. The fourth arch forms the aorta; the left sixth arch forms the left pulmonary artery and duct. The fifth aortic arch is a transient developmental structure in humans as there is no 5th pharyngeal arch; indeed, its existence has, in the past, been disputed (1). There are some reports of persistence of the 5th embryonic arch artery (2,3), but it is rare. This may, in part, be due to under-recognition and misdiagnosis (2). Further insight into the development and possible persistence of the 5th arch arteries have been gained from 2 recent studies that have described the presence of vascular channels thought to represent putative 5th arch arteries in mice (4,5). These studies are of particular interest because cardiac morphogenesis in mice closely resembles that of humans. Two forms of persistent 5th arch are proposed: a systemic-to-systemic connection, and a systemic-to-pulmonary connection. It may be associated with other cardiac pathology. The latter form requires that it be differentiated with a short wide arterial duct (window duct) or an aortopulmonary (AP) window. We describe the imaging and outcomes in 2 children in whom a vascular channel was diagnosed prenatally and likely represented remnants of the 5th aortic arch artery. At 22 weeks’ gestation, fetus 1 was referred for echocardiography, which showed normal situs and concordant connections with critical pulmonary stenosis. The pulmonary valve was dysplas-