1. Effect of perianeurysmal environment on intraaneurysmal flow Szikora I *, Ugron A **, Varallyai Gy***, Marosfői M *, Berentei Zs*, Paal Gy ** *National Institute of Neurosciences, Budapest, **University of Techniques and Economics, Budapest ***MR Research Center, Semmelweis University, Budapest

2. Background The natural history of unruptured aneurysms is poorly understood Estimation of rupture risk is based on size and location only –Statistical data from ISUIA study Irregular aneurysm shape is generally considered as a sign demonstrating –local weakness of aneurysm wall –increased risk of rupture

3. Background Rupture risk is likely related –to the hemodynamic load absorbed by the aneurysm wall –to intraaneurysmal flow conditions These might be related to aneurysm morphology

4. Purpose To determine if aneurysm irregularities –are caused by material in-homogeneity of the aneurysm wall or by impressions from external anatomical structures –produce increased hemodynamic load on the aneurysm wall Represent increased risk of rupture

5. Methods and materials 12 supraclinoid ICA aneurysms studied –DSA Rotational angiography - 3D reconstruction –Simulation: Finite volume modeling Flow simulation (ANSYS CFX 10.0) –MRI / MRA Philips Achiva 3T magnet Cisternography: T2W 3D DRIVE TOF MRA

6. Methods and materials Irregularities on aneurysmal wall were matched –with surrounding anatomy in the outside –Image fusion: MR cisternography DSA 3D model Paraview 3.6

7. Large parophthalmic aneurysm Impression caused by optic nerve

8. Image fusion

10. Double vortex at the area of impression

11. Increased WSS at impression zone

12. No increased pressure at impression zone

13. Results: morphology Irregular aneurysm shape Irregularity caused YesNo No visible reason Optic nerve/ chiasm Skull base Arterial branch 930531

14. Large parophthalmic aneurysm Impression by optic nerve and chiasm

15. Results: flow dynamics Focal Increase of WSS dynamic pressure Impression9/92/9 No impression1/3

16. WSS Area of increased WSS

17. Dynamic pressure (systole)

18. Aneurysm surrounded by CSF space Homogeneous WSS distribution

19. Conclusion Aneurysm wall irregularities in the supraclinoid ICA region –seem to be related to impressions by surrounding anatomical structures –Rather than caused by inherent wall in- homogeneity Such impressions create focal increase of wall shear stress This may increase the likelihood of aneurysm rupture