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What is Bilateral rib notching is seen in – and explain in detail?
Radiological features of COA

Reverse figure of '3' sign or double bulge sign or E sign on the left border of aortic shadow is formed by (above downward:- Prestenotic dilatation; coarctation itself (indentation); poststenotic dilatation.
Double aortic knuckle.
Dock's sign:- There is bilateral notching of inferior margins of 3-8 ribs. Rib notching is absent in the 1st & 2nd ribs because first and second intercostal arteries do not take part in the collateral circulation. Rib notching increases with age and after the age of 7 years, rib notching is present in almost all the cases.