Expansion
Collateral flow through enlarged posterior intercostal arteries erodes the lower rib borders
Expansion
In coarctation the aorta is narrowed, classically just distal to the left subclavian artery near the ligamentum arteriosum. Blood must reach the lower body by another route:
- Subclavian artery → internal thoracic artery
- Internal thoracic → anterior intercostal arteries
- Anterior intercostals → posterior intercostal arteries, flowing backwards
- Posterior intercostals → descending aorta, below the narrowing
The posterior intercostal arteries become dilated and tortuous, and pulsate against the inferior borders of the ribs, producing the scalloped erosions known as rib notching.
The clinical counterpart is radiofemoral delay with upper limb hypertension and weak femoral pulses.