Chest radiograph of a patient with coarctation of the aorta

Posterior-anterior (PA) chest radiograph of a patient with coarctation of the aorta (A) shows soft tissue fullness in the region of the ectatic subclavian artery (arrow) and with subtle rib notching best appreciated in the fourth right rib (arrowhead). The lateral examination (B) shows the characteristic 3 sign consisting of the enlarged and distorted aortic knob and subclavian artery forming the upper portion of the 3, the waist at the site of the coarctation (arrow), and the lower portion formed by the post-stenotic dilatation of the proximal descending aorta.