Answer is C (Coarctation of Aoa) Rib notching and double bulge sign are characteristic radiological signs of coarcation of aoru Signs in coarctation of aoa Abnormal Aoic arch Commonest finding Site of narrowing may be seen as an identation. e Classic '3 signQ or double bulge sign' Q on left border of aoic shadow is formed by (above downwards) - prestenotic dilatation - coarctation itself (indentation) - poststenotic dilatation Inferior Rib notching Is a frequent sign in adults. It is not seen until late childhood. It is seen on the inferior margin of posterior halves of ribs from 3rd or 4th ribs downwards. Rib notching is due to enlargement of intercostal aeries which act as collateral vessels. These collateral vessels produce indentation, on the ribs at the above sites.