Immunocellular microenvironment of the vascular wall of cerebral aneurysms: What is the role of inflammatory cells in aneurysmal remodeling?

Intracranial aneurysms (IAs) may afflict up to 5% of the general population, or up to 15 million individuals in the US. The two forms of IAs that can be recognized by their shape are saccular and nonsaccular IAs, with uncommon aneurysm types, fusiform and dissecting aneurysms, comprising 13% of nonsaccular IAs. Conceivably, among the various risk factors for IA development, vessel wall inflammation represents a major cause. Accordingly, IAs may not necessarily be the result of passive widening of vessel wall structures, but may also be the result of inflammation and tissue degeneration. Thus, flow-induced vascular remodeling during IA pathogenesis may reflect immune cell infiltration and consequent release of proinflammatory cytokine, chemokine, and matrix metalloproteinase that contribute to vessel wall degeneration and weakening. Thus, infiltrating neutrophils, macrophages, T-lymphocytes and complement factors, and the resulting immune microenvironment may be pertinent in IA pathogenesis.