Introduction: Inflammation has been proposed as a possible mechanism involved in the degradation and weakening of the walls of intracranial aneurysms.
Hypothesis: Abnormal wall shear stress (WSS) levels induce wall inflammation which then affects the wall structure and mechanics
Methods: A total of 20 aneurysms which underwent surgical clipping were studied. Patient-specific computational fluid dynamics models were constructed from pre-surgical CTA images. Numerical simulations were carried out using pulsatile flows. After clipping the aneurysm, a tissue sample was resected from the dome and analyzed histologically with CD45 to search for evidence of wall inflammation. For analysis, the aneurysm series was divided in two different manners. First, aneurysms were classified into an “inflammation” group if the number of CD45+ cells was larger than the median of CD45+ cells in the entire sample of 20 aneurysms; otherwise they were classified as “no-inflammation”. Hemodynamic variables were then statistically compared between these two groups. Secondly, aneurysms were subdivided into three groups according to their mean WSS: 1) “low WSS” if WSS<0.5*median(WSS), 2) “high WSS” if WSS>2*median(WSS), and 3) “mid WSS” otherwise. The numbers of CD45+ cells in each group were then statistically compared.
Results: Aneurysms in the “inflammation” group had significantly larger mean WSS (p=0.018), shear rate (p=0.015), vorticity (p=0.018), and viscous dissipation (p=0.015) than aneurysms in the “no-inflammation” group. Conversely, aneurysms in the “high WSS” group had significantly larger numbers of CD45+ cells (p=0.0046) than the “mid WSS” and “low WSS” groups. Interestingly, aneurysms with stable flow patterns also tended to have larger numbers of inflammatory cells (p=0.040) than aneurysms with unstable flows.
Conclusion: These preliminary results suggest that there is a connection between intra-aneurysmal flow characteristics and wall inflammation in cerebral aneurysms. In particular, inflamed walls seem to be associated with higher levels of wall shear stress.