TWIN ARCH: A rare case of type III Persistent 5th aortic arch

Clinical History

A 21-day-old female presented with respiratory distress and cyanosis ten days after birth. Antenatal history was uneventful. The child had cried at birth.

Imaging Findings

CTA images show (Fig. 1) subaortic ventricular septal defect (*) and (Fig. 2) pulmonary atresia (arrow).

Reformatted CTA (Fig. 3) and Volume Rendered (Fig. 4) images show presence of vascular channel (#) seen arising from undersurface of aortic arch (AA) opposite to brachiocephalic artery origin (*) and connecting to left pulmonary artery (LPA). There is tight stenosis at insertion site (Fig. 4).

Discussion

Background:
Persistent 5th aortic arch (PFAA) is a rare anomaly, first described in 1969 as a double-lumen aortic arch. It is located below the 4th arch, which forms the right subclavian artery and the definitive aortic arch and above the 6th arch, whose derivatives are left pulmonary artery or ductus [1].

Clinical perspective:
The clinical presentation depends on whether the connection is a systemic to systemic or systemic to pulmonary system. PFAA is hemodynamically beneficial when associated with coarctation of the aorta or an interrupted aortic arch, and a systemic-to-pulmonary arterial connection is beneficial when associated with pulmonary atresia or tricuspid atresia.
Patients with right ventricular outflow obstruction develop multiple aorto-pulmonary collaterals as a way to maintain pulmonary circulation. In our case, the presence of fifth aortic arch in patients with pulmonary atresia was maintaining the pulmonary circulation, that has been postulated as an embryonal compensatory mechanism [2].

Imaging:
PFAA can be either right-sided or left-sided. There are three types [3]:
I) Double-lumen aortic arch with both lamina patent
II) Atresia and interruption of the superior arch with patent inferior (persistent fifth) arch
III) Systemic-to-pulmonary arterial connection arising proximal to the first brachiocephalic artery

Type I PFAA is the most common form. Type III has often been described in association with pulmonary atresia and ventricular septal defect. PFAA may be associated with pulmonary atresia, tricuspid atresia, coarctation of aorta, interrupted aortic arch, ventricular septal defect, patent ductus arteriosus (PDA), atrioventricular septal defect, tetralogy of Fallot, and persistent truncus arteriosus [4].

Differential diagnosis includes aortopulmonary window (APW) and PDA.
In PFAA, communicating artery connects distal to the origin of the pulmonary arteries where, as in an AP window, this would be positioned along the pulmonary trunk and bifurcation of the pulmonary arteries. A high AP window may extend to the origin of the right pulmonary artery.
A PDA would communicate distal to the arch arteries while the communicating artery in PFAA connects the aorta proximal to the origin of the head and neck vessels.

Take Home Point:
Attention should be paid to the origin and site of connection of the communicating artery to the systemic or pulmonary arterial system to differentiate PFAA from AP window or PDA.

Differential Diagnosis List

Final Diagnosis

Persistent fifth aortic arch

URL:	https://www.eurorad.org/case/14252
DOI:	10.1594/EURORAD/CASE.14252
ISSN:	1563-4086