Collateral cerebral circulation

The leptomeningeal collateral circulation (also known as leptomeningeal anastomoses or pial collaterals) is a network of small blood vessels in the brain that connects branches of the middle, anterior and posterior cerebral arteries (MCA, ACA, and PCA), with variation in its precise anatomy between individuals. During a stroke, leptomeningeal collateral vessels allow limited blood flow when other, larger blood vessels provide inadequate blood supply to a part of the brain. [Source: Wikipedia ]