Persistent 5th aortic arch--a great pretender: three new covert cases.

Although persistence of the embryonic fifth aortic arch is considered a rare congenital malformation, analysis of the records of the cardiopathological collections of the Brompton and Killingbeck Hospitals reveals 6 examples in approximately 2000 specimens, an incidence amongst our material of 1 in 330. Since our review of the literature reveals only a further 13 described cases, we wonder if the condition may go unrecognized rather than being exceedingly rare. This possibility is further supported by the fact that 3 of our cases were incorrectly interpreted when initially described. In this report, we describe the details of 2 of these specimens and one other case that was not included in our earlier descriptions of this malformation. The first case had the persistent fifth arch as a conduit between the pulmonary and systemic circulations in the setting of aortic atresia with interruption of the aortic arch. The second case demonstrated a double lumen aortic arch, the fifth arch in this instance being an accessory systemic-to-systemic conduit. In the final case, the persistent arch was initially considered to represent an aorto-pulmonary window but review revealed an aortic to pulmonary conduit more in keeping with the presence of a fifth arch. We conclude that the powers of mimicry of this enigmatic structure may account for its apparent rarity.