1. Radiology department, Kasr Alainy teaching hospitals, Cairo University, Egypt.
2. Fetal medicine unit, Cairo University, Egypt.

Case report

A 31-year old patient (G1P0) with unremarkable medical history was referred at 38 weeks gestation for routine ultrasound.

Our examination revealed the following:

• Moderate size discrepancy between both ventricles with dominant RV (dilated and hypertrophied). The apex of the heart is still formed by the anechoic lumen of the left ventricle denoting normal LV growth and no evidence of hypoplasia.
• The main pulmonary artery appeared dilated compared with the ascending aorta.
• The arterial duct was seen aneurysmally dilated compared with narrow and elongated transverse aortic arch.
• The isthmic portion of the aortic arch showed focal stenotic lesion opposite to its junction with the arterial duct just after to origin of left subcalvian artery.
• Color and pulsed Doppler study showed protodiastolic reversal flow in the transverse aortic arch.

Our final diagnosis was tubular hypoplasia of the aortic arch with critical coarctation.

Normal for age baby (3220+/-430gm) was delivered through a C- section and mechanically ventilated due to respiratory distress. Postnatal echocardiography revealed significant tubular hypoplasia of transverse aortic arch measuring 3 mm in maximum side to side diameter with focal tight isthmic narrowing and moderate patent ductus arteriosus. Small mid muscular ventricular septal defect 3 mm was also noted. At least 2 pulmonary veins were confirmed to enter left atrium excluding the presence of TAPVD.

Surgical consultation stated that neonatal intervention is recommended after stabilization of patient general condition. IV prostaglandin infusion was done for maintenance of ductal dependant systemic circulation till improvement of neonatal general condition.

Images 1-4; videos 1-5: 2D images of the fetal heart show dilated hypertrophied right ventricle, dilated main pulmonary artery and ductus arteriosus compared to ascending aorta and aorta isthmus.

Images 5, 6, 7: sagital doppler images of the fetal heart show tubuar hypoplasia of the aortic arch with tight isthmic coarctation on 2D, color and pulsed Doppler studies axial and Sagittal views.

Image 8: pulsed doppler image in sagital plane shows tubular hypoplasia of the aortic arch with tight isthmic coarctationand reversed flow.

Videos 6-9: sagital doppler images of the fetal heart show tubuar hypoplasia of the aortic arch with tight isthmic coarctation on 2D, color and pulsed doppler studies axial and sagittal views.

Image 9 and 10: pulsed doppler images show normal umbilical artery flow with relatively low cerebral blood flow resistance.

Discussion:

Relatively low resistance cerebral blood flow as noted by MCA doppler parameters compared with gestational age raises the suspicion of fetal growth restriction with ventricular disproportion secondary to severe placental insufficiency. However, with normal umbilical artery flow resistivity, average amniotic fluid, good gross body movements and normal fetal growth parameters, fetal growth restriction was unlikely to be the cause of this moderate ventricular disproportion. Despite advanced gestational age and limited echo window, further evaluation of fetal cardiac anatomical structures revealed significantly hypoplastic distal and isthmic portion of aortic arch (transverse arch) compared with the aneurysmally dilated ductus arteriosus with estimated isthmus/ductus ratio less than 0.3 and evident protodiastolic reversal flow in the aortic arch. These findings could explain low resistivity of cerebral blood flow that was attributed to relatively low flow in the aortic arch secondary to tight obstructive lesion with consequent flow reversal in the aortic arch which indirectly guided us to the urgent IV prostaglandin infusion to maintain ductal dependant systemic circulation.