Rib notching is seen in?

Ans. (a) Coarctation of aortaRef: Harrison 19th ed. /1525* By far the most common cause of rib notching. It Usually involves the posterior 4th - 8th Ribs.* Collateral flow bypassing the aortic constriction to reach the abdomen and lower extremities comes almost entirely from the two subclavian arteries via the thyrocervical, costocervical, and internal mammary arteries and their subdivisions to the posterior intercostals and then into the descending aorta. The large volume of blood traversing this route causes dilatation, tortuosity, and increased pulsation of the intercostal arteries, which result in gradual erosion of the adjacent bones