What structure is primarily responsible for maintaining collateral perfusion?

The structure primarily responsible for maintaining collateral perfusion is the Circle of Willis. This circular network of arteries is located at the base of the brain and plays a crucial role in ensuring adequate blood flow to the cerebral hemispheres, even if one of the primary arteries becomes occluded or narrowed.

The Circle of Willis connects the internal carotid arteries and the vertebral arteries through several important communicating arteries, allowing for alternative pathways for blood to reach various parts of the brain. This configuration is critical in preserving cerebral perfusion under conditions where one vessel may not be functioning optimally.

Other structures mentioned, while important in their respective roles, do not serve the same function in terms of maintaining overall collateral blood flow to the brain. The spinal cord, brachial plexus, and cauda equina are involved in different aspects of neural function and vascular supply but do not contribute to the protective circulatory redundancy provided by the Circle of Willis.