Focal Aneurysm Wall Enhancement on Magnetic Resonance Imaging Indicates Intraluminal Thrombus and the Rupture Point

The precise mechanism of aneurysm wall enhancement (AWE) in ruptured intracranial aneurysms on magnetic resonance vessel wall imaging (VWI) remains unclear. We explored patterns of VWI findings and correlations with intraoperative or histopathologic aneurysm wall architecture. Twenty-four patients were evaluated by VWI before microsurgical clipping or endovascular coiling. The patterns of AWE were categorized, and the contrast ratio of AWE area was measured relative to the pituitary stalk. A total of 13 aneurysms were microsurgically inspected of the aneurysm wall and 4 were available for histopathologic evaluation. AWE was identified in 20 of 24 ruptured aneurysms. Among these 20 aneurysms, AWE was focal in 15 and circumferential in 5. Focal AWE showed significantly higher contrast ratio than circumferential AWE (P = 0.002). Histopathologic studies suggested that focal AWE indicating contrast ratio over 0.1 could be associated with fresh intraluminal thrombus at the rupture site. On the contrary, circumferential AWE suggested potential wall thickening with abundant neovascularization and inflammatory cells. Two AWE patterns were seen in ruptured intracranial aneurysms. Focal AWE on magnetic resonance imaging might indicate the presence of intraluminal thrombus, and detection of this sign could be useful for identification of the rupture point before treatment.