Which collateral pathway is NOT considered a main route in the case of ICA obstruction?

The collateral pathways of the vascular system play a crucial role in maintaining blood flow when a primary route, such as the internal carotid artery (ICA), becomes obstructed. Each of the mentioned collateral pathways serves a specific function and is classified based on how it compensates for the reduced blood flow.

The pathway from the genicular to arcuate branches, while important in certain contexts, is not primarily recognized as a main collateral route in cases of ICA obstruction. This pathway is more associated with the anastomoses around the knee and related to the lower extremities, particularly in the context of limb perfusion. Therefore, it does not effectively counterbalance ICA obstruction, which typically relies on pathways that provide direct compensation for cerebral blood flow.

On the other hand, pathways like the internal mammary to circumflex branches, vertebral to basilar arteries, and cervical to intracranial circulation are more integral to maintaining cerebral perfusion in conditions where the ICA is compromised. The internal mammary artery can provide collateral flow to the coronary system, but also plays a role in cranial circulation under certain conditions. The vertebral artery's connection to the basilar artery allows for significant collateral flow to the posterior circulation of the brain, which can be particularly critical if