In case of IVC obstruction the collaterals which open up are all except
**Core Concept**
Intravascular collateral circulation is a vital compensatory mechanism that develops in response to significant obstruction of major veins, such as the inferior vena cava (IVC). This collateral network allows for alternative pathways for blood flow, thereby alleviating venous congestion and pressure.
**Why the Correct Answer is Right**
When the IVC is obstructed, several collateral pathways open up to bypass the obstruction. The hepatic veins, which normally drain directly into the IVC, create a collateral circuit with the azygos and hemiazygos veins. This collateral pathway is known as the azygos-hemiazygos system. The azygos system is a vital route for collateral circulation in cases of IVC obstruction, allowing blood to flow from the lower body to the heart via the superior vena cava.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not a known collateral pathway in the context of IVC obstruction.
* **Option B:** This option is incorrect because it is not a direct collateral pathway in the context of IVC obstruction; while it may be involved in other types of venous obstruction, it is not the primary pathway in IVC obstruction.
* **Option D:** This option is incorrect because it is not a collateral pathway that opens up in response to IVC obstruction; it is a different type of venous structure altogether.
**Clinical Pearl / High-Yield Fact**
The azygos-hemiazygos system is a critical collateral pathway in cases of IVC obstruction, and its development is essential for maintaining adequate venous return to the heart.
**Correct Answer: C.**