Step I Question about Rib notching with Postductal Coarctation

[DeeJay2728]

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I'm having trouble understanding why there's Rib Notching with Postductal Coarctation if 9 of the 11-12 pairs of intercostal arteries originate on the posterior side of the Aorta AFTER the Coarctation (The Pressure in those arteries will be lower). Where do the collaterals come from, and why would they cause Notching? I can see how the first and second ribs would have notching, due to the increased pressure in the Subclavian arteries, Costocervical trunk and ultimately the first and second posterior intercostal arteries (They'd be engorged and would cause erosion of the inferior ribs). Please Explain!?!?

 

[acciddropping]

The collaterals are from the aorta, and the corctation of the aorta increases the back pressure - hence, those collaterals that run under the ribs became engorged (swollen), appearing notches. You may also feel pulses on the ribs.

 

[DeeJay2728]

Are the collaterals coming off the aorta after or before the coarctation?

 

[alicealicealice]

See below and see if that makes sense...

Note: Normal blood flow is from the from the external iliac into the inferior hypogastric. Now there is blood coming from the Internal Thoracic-->Superior Epigastric--(anastamosis)-->Inferior epigastric-->External iliac-->supplying Lower extremities (whihc are starved due to coarctation)

 

[DeeJay2728]

Thank you!!! Just to make sure I got this right... The blood flow that normally originates from posterior Aorta is now REVERSED bc of the increased pressure in the subclavian and internal thoracic arteries (this forces blood to go INTO the posterior Aorta via the intercostal arteries)

 

[DeeJay2728]

That now makes sense as to why the intercostal arteries are now engorged and cause erosion... Thanks again!!!

 

[acciddropping]

Are the collaterals coming off the aorta after or before the coarctation?

I was actually confused with intercostal aa that are coming out from the aorta.. the above post explained it all.. In Pathoma, he drew as if the collateral came out from aorta but the above chart makes sense more..

 

[alicealicealice]

Thank you!!! Just to make sure I got this right... The blood flow that normally originates from posterior Aorta is now REVERSED bc of the increased pressure in the subclavian and internal thoracic arteries (this forces blood to go INTO the posterior Aorta via the intercostal arteries)

Exactly. The underlying principle is that the aorta is blocked after the subclavian. So blood flow backs up and now goes:
Subclavian-->Internal thoracic-->Anterior Intercostals--anastamosis-->Posterior Intercostals--reversed blood flow-->aorta-->viscera/lower body
Subclavian-->Internal thoracic-->Superior Epigastic--anastamosis-->Inferior epigastric--reversed blood flow-->external iliac-->lower body

 

[DeeJay2728]

Thank you so much!!!