<prompt> Rib Notching of 49th ribs with double bulging is seen inAortic aneurysmAortic dessectionCoarctation of aortaDiaphragmatic hernia  <response>: Radiological findings of COA1. Abnormal Aortic arch : Commonest findingSite of narrowing may be seen as an identation.Classic 3 sign or double bulge sign on left border of aortic shadow is formed by above downwardsPrestenotic dilatationCoarctation itself indentationPoststenotic dilatation2. 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 3n1 or 4th ribs downwards. Rib notching is due to enlargement of intercostal arteries which act as collateral vessels. These collateral vessels produce indentation, on the ribs at the above sites. 