Regional Aneurysm Wall Enhancement is Affected by Local Hemodynamics: A 7T MRI Study

Aneurysm wall enhancement regions tend to have lower wall shear stress than nonenhanced regions of the same aneurysm. The association between flow conditions and aneurysm wall enhancement seems to depend on the location of the region on the aneurysm sac. Regions at the neck and close to the inflow tend to be exposed to higher wall shear stress and wall shear stress gradients. BACKGROUND AND PURPOSE: Aneurysm wall enhancement has been proposed as a biomarker for inflammation and instability. However, the mechanisms of aneurysm wall enhancement remain unclear. We used 7T MR imaging to determine the effect of flow in different regions of the wall. MATERIALS AND METHODS: Twenty-three intracranial aneurysms imaged with 7T MR imaging and 3D angiography were studied with computational fluid dynamics. Local flow conditions were compared between aneurysm wall enhancement and nonenhanced regions. Aneurysm wall enhancement regions were subdivided according to their location on the aneurysm and relative to the inflow and were further compared. RESULTS: On average, wall shear stress was lower in enhanced than in nonenhanced regions (P?=?.05). Aneurysm wall enhancement regions at the neck had higher wall shear stress gradients (P?=?.05) with lower oscillations (P?=?.05) than nonenhanced regions. In contrast, aneurysm wall enhancement regions at the aneurysm body had lower wall shear stress (P?=?.01) and wall shear stress gradients (P?=?.008) than nonenhanced regions. Aneurysm wall enhancement regions far from the inflow had lower wall shear stress (P?=?.006) than nonenhanced regions, while aneurysm wall enhancement regions close to the inflow tended to have higher wall shear stress than the nonenhanced regions, but this association was not significant. CONCLUSIONS: Aneurysm wall enhancement regions tend to have lower wall shear stress than nonenhanced regions of the same aneurysm. Moreover, the association between flow conditions and aneurysm wall enhancement seems to depend on the location of the region on the aneurysm sac. Regions at the neck and close to the inflow tend to be exposed to higher wall shear stress and wall shear stress gradients. Regions at the body, dome, or far from the inflow tend to be exposed to uniformly low wall shear stress and have more aneurysm wall enhancement.