Obscured aortic arch on the lateral view as a sign of coarctation

Forty patients with coarctation of the aorta were compared with 80 normal subjects matched by sex and age. The aortic arch was invisible on the lateral radiograph in 84% of patients preoperatively and 88% postoperatively. Only 6 normal subjects (8%) had a similar finding. The authors conclude that an obscured aortic arch on the lateral view could be a clue to the presence of coarctation. Possible explanations for this phenomenon include (a) dilatation of the brachiocephalic arteries (particularly the left subclavian artery), obscuring the superior margin of the arch; (b) hypoplasia and anteromedial displacement of the distal portion of the arch; and (c) diffuse hypoplasia of the arch combined with focal coarctation.