English: Impact of collateral flow on clot lysis and reperfusion. (a) Schematic drawing of the collateral network showing anastomoses between the middle cerebral artery (MCA) and anterior cerebral artery Impact of collateral flow on clot lysis and reperfusion. (a) Schematic drawing of the collateral network showing anastomoses between the middle cerebral artery (MCA) and anterior cerebral artery (ACA); (b) in stroke with a poor collateral network, the collaterals fail to fill and insufficiently compensate the flow reduction after arterial occlusion; (c) a collateral enhancement occurring in patients showing good collateral network. The flow in the collaterals changes direction and allows the thrombolytic to reach the drug from different sides.