A 25-year-old female had presented for a routine third-trimester scan. The fetus corresponded to 35 weeks gestational age by fetal biometry. Dilated and hypertrophied right ventricle was noted in 4 chamber view and hence detailed fetal echo was performed. 3 vessel trachea view shows dilated pulmonary trunk with hypoplastic ascending aorta. Ductal arch view shows normal ductal arch with normal flow pattern and velocities in ductus arteriosus. Aortic arch view shows hypoplastic aortic arch with aortic arch interruption between left common carotid and left subclavian artery.

These imaging findings are highly suggestive of aortic arch interruption type B. Less likely differential diagnosis is severe coarctation of aorta. The left subclavian artery and descending aorta are receiving blood from the ductus arteriosus. There was no associated ventricular septal defect or aortopulmonary window. There was no systemic venous hypertension and no changes of hydrops fetalis. The fetus was delivered at term and expired on the first neonatal day.

Interrupted aortic arches are classified according to the site of interruption relative to the brachiocephalic vessels:

• type A: interruption distal to the left subclavian artery (2nd most common)
• type B: interruption distal to the left carotid artery (most common)
• type C: interruption distal to the brachiocephalic artery