Visualization of luminal thrombosis and mural Iron accumulation in giant aneurysms with Ex vivo 4.7T magnetic resonance imaging

Background: Better diagnostic tools to identify rupture-prone saccular intracranial aneurysms (sIA) are needed. Inflammation and luminal thrombus associate with degeneration and rupture of the sIA wall. Iron-uptake has been detected in the inflammatory cells of the sIA wall and thrombus is the likely source of this iron. We investigated ex vivo the use of magnetic resonance imaging (MRI) to detect iron accumulation and luminal thrombus in giant sIAs.

Methods: Giant sIAs (n = 3) were acquired from microsurgical operations, fixed with formalin, embedded in agar and imaged at 4.7T. Samples were sectioned maintaining the orientation of the axial plane of MRI scans, and stained (hematoxylin-eosin and Prussian blue).

Results: All three giant sIAs showed a degenerated hypocellular wall with both mural and adventitial iron accumulation and displayed different degrees of luminal thrombus formation and thrombus organization. Signal intensity varied within the same sIA wall and associated with iron accumulation in all tested sequences. Wall areas with iron accumulation had significantly lower signal to noise ratio (SNR) compared with areas without iron accumulation (P = 0.002). Fresh and organizing thrombus differed in their MRI presentation and differed in signal intensity of the aneurysm wall (P = 0.027).

Conclusion: MRI can detect ex vivo the accumulation of iron in giant sIA wall, as well as fresh and organizing luminal thrombus. These features have been previously associated with fragile, rupture-prone aneurysm wall. Further studies of iron accumulation as a marker of rupture-prone aneurysm wall are needed.