Serial magnetic resonance imaging of acute spontaneous thrombosis of a giant intracranial aneurysm--case report.

A 46-year-old female presented with decreased bilateral visual acuity due to an unruptured non-thrombosed giant aneurysm arising from the left internal carotid artery. After admission, acute thrombosis of the aneurysm occurred spontaneously. Her consciousness and visual acuity temporarily worsened. Serial T2-weighted magnetic resonance (MR) imaging showed the size of the low intensity area near the orifice increased, and the aneurysm ruptured thereafter. Trapping of the aneurysm with a high-flow bypass was performed. Serial MR imaging findings clearly demonstrated the intraluminal structure of the thrombosed giant aneurysm. The aneurysm grew in size after thrombosis. The enlarging signal-void area on T2-weighted MR images were indicative of aneurysmal rupture. MR imaging is quite helpful to evaluate the changes of intraluminal thrombosis and size in giant aneurysms.