In case of coarctation of aoa which of the following is not involved in collateral formation?
**Core Concept**
Coarctation of the aorta is a congenital condition characterized by the narrowing of the aortic isthmus, leading to obstructed blood flow to the lower body. The body compensates by developing collateral blood vessels to bypass the obstruction.
**Why the Correct Answer is Right**
Collateral circulation in coarctation of the aorta involves the intercostal arteries, which arise from the costocervical trunk and the superior intercostal artery from the subclavian artery. These arteries anastomose with the posterior intercostal arteries, which in turn anastomose with the lumbar arteries, thereby establishing a collateral pathway. The circle of Willis is also involved in collateral circulation, particularly in the presence of significant coarctation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the internal thoracic artery (also known as the internal mammary artery) does play a role in collateral circulation in coarctation of the aorta, particularly through its anastomosis with the posterior intercostal arteries.
* **Option B:** This option is incorrect because the inferior mesenteric artery does contribute to collateral circulation in coarctation of the aorta, particularly through its anastomosis with the superior mesenteric artery.
* **Option C:** This option is incorrect because the circle of Willis is indeed involved in collateral circulation in coarctation of the aorta, particularly in the presence of significant coarctation.
**Clinical Pearl / High-Yield Fact**
The presence of a "notching" of the ribs on chest X-ray is a classic sign of coarctation of the aorta, resulting from the erosion of the ribs by the enlarged intercostal arteries.
**Correct Answer:** D