<prompt> Ribnotching of 4-9th ribs with double bulging is seen in -Aoic aneurysmAoic dessectionCo - arctation of aoaDiaphragmatic hernia  <response>: Ans. is c i.e., Coarctation of Aoa Radiological findings of COA 1. Abnormal Aoic arch : Commonestfinding Site of narrowing may be seen as an identation. Classic 3 sign or double bulge sign on left border of aoic shadow is formed by above downwards Prestenotic dilatation Coarctation itself indentation Poststenotic dilatation 2. 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 3d 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. 