This finding showed similarity to intracranial aneurysm wall that activated macrophages secrete TNF-α, which amplify a pro-inflammatory downstream gene expression such as MCP-1, COX2, and MMP-9 either via TNF-TNFR1 67-70 or NF-κB pathways 71-73. Here, MMP9 is linked to Dilatation of the cerebral artery.