PECAM1 and Stroke: As the expected acute leptomeningeal arteriogenesis, defined as the activation of leptomeningeal collaterals, is rather dominated by the action of monocytes [40] and circulating CD31+/CD34+ stem cells would not integrate into the vessel wall as seen here [41], we postulate that this represents an additional angiogenetic potential of the leptomeningeal vasculature in the regenerative phase after stroke.