Tetralogy of fallot with persistent fifth aortic arch: echocardiographic diagnosis.

Although persistent, fifth aortic arch (P5A) is an uncommon anomaly. Its incidence is unknown due largely to failure of recognition. Fundamental to its diagnosis is an adequate understanding of the various settings in which P5A may manifest. One of the more frequently reported manifestations of this unusual anomaly is a systemic-to-pulmonary connection in the presence of pulmonary atresia, with or without a ventriculoseptal defect. This report describes a new case of P5A in an infant with tetralogy of Fallot but not pulmonary atresia, which was diagnosed echocardiographically. The echo-Doppler characteristics of P5A in the presence of right ventricular outflow obstruction are described, and the implications regarding surgery for the accompanying defects are discussed. To the authors' best knowledge, the described case is the first reported instance of P5A in this specific setting.