Final Answer:
Classic radiographic findings of aortic coarctation include "3 sign" and rib notching.
Step-by-step explanation:
The "3 sign" is a classic radiographic finding in aortic coarctation, visible on a chest X-ray. It refers to the characteristic appearance of the aortic knob, resembling the number 3, resulting from the post-stenotic dilation of the aorta. This sign indicates the narrowing of the aorta typically seen in aortic coarctation.
Rib notching is another radiographic feature associated with aortic coarctation. It results from collateral blood flow, leading to erosion and notching of the inferior surface of the ribs. Rib notching is often more pronounced in the lower ribs and is a consequence of the increased blood flow through intercostal arteries as a compensatory mechanism.