Abstract: Objective To investigate the expression of matrix metalloproteinase-9 (MMP-9) in the arachnoid membrane around
posterior communicating artery aneurysms. Methods Twelve patients with posterior communicating artery aneurysms
undergoing surgical intervention in our hospital between November, 2010 and November, 2011 were enrolled as the case
group along with 6 concurrent patients with severely head trauma or epilepsy as controls. The expression of MMP-9 in the
aneurysmal walls and the arachnoid membrane was examined in immunohistochemistry, and HE staining and Sirus red
staining were performed to examine the pathological changes. Results The perianeurysmal arachnoid membrane showed
tissue destruction and disruption of the connections between the membrane and the artery wall with local detachment.
Compared with that in the control group, the level of MMP-9 in the arachnoid membrane was significantly higher in the case
group (P<0.05), but significantly lower than that in the aneurysm wall within the same sample (P<0.05). No differences were
found in the levels of MMP-9 in the aneurysm patients with different ages or Hunt-Hess scale scores. Conclusion MMP-9 is
closely related with the formation of posterior communicating artery aneurysms by causing degradation of extracellular
matrix of the vascular wall and the arachnoid membrane.