Persistent fifth aortic arch: an ignored and underestimated disease.

We report two unique cases of persistent fifth aortic arch with a systemic-to-pulmonary connection. All previously reported cases with such a connection in the literature have either been cases of pulmonary atresia or an aortic arch anomaly, and the existence of a fifth aortic arch was a benefit to the underlying great vessel anomaly. However, our two cases did not have this associated great vessel anomaly, and the fifth arch resulted in a large left-to-right shunt with severe pulmonary hypertension and heart failure. The first case was misdiagnosed preoperatively; an accurate diagnosis was made after cardiac surgery. Because of its rarity and complexity, a persistent fifth aortic arch is often ignored and misdiagnosed.