Abstract 44: Histopathological Interpretation of Vessel Wall Imaging of Intracranial Aneurysms

Abstract

Background and purpose: It remains a challenge to predict unruptured intracranial aneurysms (UIAs) that are prone to rupture. MR- Vessel wall imaging (VWI) is a current topic whether it could predict unstable aneurysms. We investigated the correlations between aneurysm wall imaging findings and aneurysmal risk factors with a focus on the histopathological vessel wall architecture to clarify the interpretation of VWI of intracranial aneurysms. Methods: A total of 117 intracranial aneurysms, including 21 ruptured and 96 UIAs were investigated by VWI and visualization of the aneurysm wall enhancement (AWE) was evaluated. Univariate analysis was performed to assess the correlation between VWI findings and the PHASES score (calculating patient demographic and aneurysm morphologic risk factors). Fifteen intracranial aneurysms, including 6 ruptured and 9 UIAs were available for histopathological examination. Results: In UIAs, AWE was identified in 30 of 96 UIAs (31%). The PHASES score was associated with AWE (9.1 ± 0.7 versus 6.0 ± 0.3, p= 0.001). Histopathological studies revealed that wall thickening accompanied by atherosclerosis, neovascularization, and macrophage infiltration corresponded to AWE. The thicken wall was characterized by loss of mural cells and mucinous degeneration as well. On contrary, AWE was identified in 17 of 21 ruptured aneurysms (81%). Three AWE patterns (focal, circumferential, and both) were identified in ruptured ones. Histopathological studies revealed that focal AWE was associated with very thin aneurysm wall and fresh intraluminal thrombus at the rupture site, whereas circumferential AWE suggested wall thickening with abundant neovascularization and inflammatory cells. Conclusions: In the present study, one-third of UIAs showed AWE and might not provide informative rupture risk estimation beyond PHASES score at this moment. However, VWI of intracranial aneurysms can detect what is going on in the aneurysm wall. Histopathological interpretation of VWI in ruptured aneurysms differed from that of UIAs, especially in focal AWE. Focal AWE could identify the intraluminal thrombus suggesting rupture site of the wall before treatments.