Repeat routine differential pulmonary blood flow measurements in congenital heart disease by MR: interstudy variability and benchmark of a clinically relevant change.

AP window. The baby was born at term in good condition, and postnatal echocardiography was consistent with prenatal diagnosis. Computed tomography angiography (Fig. 2) was consistent with the remnant of a persistent 5th arch artery, and successful surgery was performed. The features in case 1 suggested the likely diagnosis of persistent 5th arch rather than an AP window because the AP communicating artery was connecting distal to the origin of the pulmonary arteries. In an AP window, this would be positioned along the pulmonary trunk and bifurcation of the pulmonary arteries. A high AP window may extend to the origin of the right pulmonary artery, but the window is not in the form of a channel with a length resembling a vessel. Moreover, the characteristic wall structure of the arterial duct identified at surgery in our case supported the likely origin of the vessel as a remnant of the fifth arch artery. For the second case, the differentiating point from an arterial duct was the location of the communicating artery connecting the aorta proximal to the origin of the head and neck vessels; an arterial duct would communicate distal to the arch arteries. Both fetuses reported here likely had vascular channels that represented remnants of a 5th aortic arch artery. Failure to diagnose aortic interruption with persistence of the 5th arch arterial channel in our first case resulted in prolonged surgery and subsequent demise. Lessons learned from this case led to appropriate considerations in the second fetus, confirmation by postnatal imaging, and appropriate surgery that resulted in a good outcome. Although postnatal reports of a persistent 5th arch artery exist (2), we have demonstrated that fetal diagnosis is possible and that additional imaging, such as computed tomography angiography, is useful to confirm prenatal diagnosis after birth and aid its successful surgical management.