What is 'figure of 3' sign?
It is an imaging finding of coarctation of aorta seen on a plain PA radiograph. Figure of 3 is formed by prestenotic dilated aorta, an indrawn segement of aorta and poststenotic dilated part of aorta.
What is reverse 'figure of 3 'sign?
It a similar finding seen on a left anterior oblique radiograph taken during barium swallow study.
Rib notching affects which ribs in coarcation of aorta?
4th to 8th ribs are involved. 3rd and 9th may be involved. However 1st and 2nd are spared as these intercostal arteries are not direct branches of thoracic aorta and hence do not form a part of the collateral pathway. They are branches of the costocervical trunk and hence they are spared.