Collateral circulation

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Collateral circulation is when an area of tissue or an organ has a number of different pathways for blood to reach it. This is often as a result of anastamoses - branches formed between adjacent blood vessels.

An example of the usefulness of collateral circulation is a systemic thrombo-embolism in cats. This is when a thrombosis lodges above the external iliac artery, blocking the external and internal iliac arteries and effectively shutting off all blood supply to the hind leg. Even though the main vessels to the leg are blocked, enough blood can get to the tissues in the leg via the collateral circulation in order to keep them alive.