Collaterals and stroke reperfusion: Too few leads to too much.

Adequate reperfusion after ischemic stroke is a major determinant of functional outcome yet remains unpredictable and insufficient for most survivors. In this issue of Neuron, Binder et al. 1 identify leptomeningeal collaterals (LMCs) in mice and human patients as a key factor in regulating reperfusion and hemorrhagic transformation following stroke.