MMP9 and meningioma: Iwado’s group, in a retrospective study of 60 grade I meningiomas, showed that VEGF levels were directly proportional to the development and extent of PTBE (p-value = 0.0397); interestingly, they also analyzed the relationship between metalloprotease-9 (MMP-9) and PTBE, and together VEGF and MMP-9 correlated with PTBE presence (p-value = 0.062, not statistically significant), potentially inducing the disruption of the arachnoid membrane and formation of the pial blood supply [71].