#eP-153: Geometric and Hemodynamic Change after Aneurysm Rupture: A Case Study

1. INOVA • Fairfax • Hospital • #eP-153: Geometric and Hemodynamic Change after Aneurysm Rupture: A Case Study • Christopher M. Putman1, Bong Jae Chung2, Farid Hamzei-Sichani3, Juan R. Cebral2 • 1Interventional Neuroradiology • Inova Fairfax Hospital • 2Department of Bioengineering • Volgenau School of Engineering • George Mason University • 3Interventional Neuroradiology • Mount Sinai Hospital • christopher.putman@inova.org

2. Disclosures Speaker for Penumbra Consultant for Codman Neurovascular NIH Funding

3. Introduction Cerebral aneurysms present important treatment challenges for patients and physicians involved in their care. Outcomes of patients with ruptured cerebral aneurysms are generally poor, with a mortality rate of approximately 20% due to the initial hemorrhage and with further significant mortality for those who are fortunate enough to survive the initial ictus and to undergo treatment. Increasingly cerebral aneurysms are found prior to rupture The risks of treatment must be very carefully weighed against the natural history risk of the aneurysm in order to recommend the path of least risk.

4. Introduction Considering that most aneurysms never go on to rupture, it is critical to best select those aneurysms at the highest future risk. A multitude of factors are generally considered including: size location morphological characteristics of the aneurysm, as well as any evidence of aneurysm growth on serial imaging, the age of the patient any personal or family history of a SAH and other factors 1. • 1. Thompson BG et al. Guidelines for the management of patients with unruptured intracranial aneurysms: A guideline for healthcare professionals from the American heart association/American stroke association. Stroke 2015;46:2368-400.

5. Introduction Computational fluid dynamics (CFD) has the potential to help predict which aneurysms are at high risk of future rupture2 Much of the current CFD literature is based on the comparison of hemodynamics of ruptured to unruptured aneurysms. Researchers have used the results of these studies to make generalized statements about which pre-rupture hemodynamic conditions are associated with future rupture. These studies rely on the assumption that the event of aneurysm rupture does not result in a significant change in the aneurysmal geometry. • 2. Cebral JR et al. Characterization of cerebral aneurysms for assessing risk of rupture by using patient-specific computational hemodynamics models. AJNR Am J Neuroadiol 2005;26:2550-9.

6. Purpose: Study the geometrical and hemodynamic characteristics in a cerebral aneurysm using anatomy defined by 3D rotational angiography preformed pre and post the aneurysms rupture. Test the assumption that aneurysmal rupture does not cause significant change in geometric and hemodynamic measures

7. Patient 42 y/o male initially diagnosed with an unruptured cerebral aneurysm on non-invasive imaging for headaches. Cerebral angiography was performed with rotational 3D angiography [Figure 1] Several weeks later prior to treatment he presented with a HH II SAH and cerebral angiography repeated and endovascular treatment performed [Figure 1]

8. Figure 1: 3D rotational angiography images before (left) and after (right) aneurysm rupture.

9. Methods: Computational fluid dynamics (CFD) models of pre and post rupture were constructed from the corresponding 3DRA images2. 3DRA images were filtered in order to reduce noise and a seeded growing algorithm was used for segmentation in order to reconstruct the arterial network topology. This was then subjected to an iso-surface deformable model to recover the vascular geometry. These vascular models were subsequently smoothed and the vessel branches were truncated at planes orthogonal to their axes. • 2. Cebral JR et al. Characterization of cerebral aneurysms for assessing risk of rupture by using patient-specific computational hemodynamics models. AJNR Am J Neuroadiol 2005;26:2550-9.

10. Methods: Numerical simulations based on 3D incompressible Navier-Stokes equations were performed using pulsatile flow conditions. Typical flow boundary conditions for a healthy subject derived from phase-contrast MRI were scaled with the inlet cross-sectional areas to achieve a mean WSS of 15 dynes/cm2 and prescribed at the inlets for all the models. Fully developed velocity profiles were prescribed at the inlets by using the Womersley solution.

11. Methods: Assumptions Newtonian viscosity for blood Rigid vessel walls.   The simulations had a minimum mesh resolution of 200 µm and a time resolution of 0.01 sec and were run for two cardiac cycles using an in-house fully implicit finite-element solver. [Figure 2] Flow variables were computed from the results of the second cycle to characterize the flow conditions within the aneurysms.  Geometric variables were computed from the 3D anatomical models.

12. Figure 2: Flow visualization at peak systole before (top row) and after (bottom row) aneurysm rupture. • Left to right: vortex corelines, isovelocity surfaces, flow streamlines, wall shear stress, oscillatory shear index.

13. Results: The 3D rotational angiography images demonstrate a viable change in aneurysm anatomy pre and post rupture (Figure 1). There has been a loss of volume with contraction of the aneurysm dome while maintaining general shape.

14. Results: Qualitatively, flow patterns are maintained with complex flow patterns pre and post. Location of flow stream compaction and regions under high WSS are unchanged but with reduction of the intensity of WSS

15. Table 1: Geometric and hemodynamic variables before and after aneurysm rupture.

16. Results: Geometric variables were all decreased ranging from 12-20% but with relative preservation of the neck size. Neck area is increased by 20% Hemodynamic variables show large reductions more pronounced in high flow variables. Relative preservation Vortex Coreline Length and POD Entropy

17. Figure 3: Ratio of aneurysm values computed after rupture over values computed before rupture for different geometric (gray bars) and hemodynamic (black bars) quantities.

18. Discussion: Pre and post rupture evaluation of this single cerebral aneurysm shows a measurable change in the dome size with relative preservation of the dome geometry. Only the neck area is increased. Hemodynamic variable are consequently effected by a consistent reduction in high flow variables and relative preservation of variables related to flow structure (coreline and POD entropy). Flow structure (used for previously qualitative classifications for rupture risks) are likely preserved because of the overall retention of the dome and neck shape with counter acting effects in reduction of volume and neck area enlargement.

19. Discussion: For quantitative variables the neck area enlargement appears to more than make up for the expect changes from volume loss resulting in a relative diffusing of the inflow stream. This case has important implications in the interpretation of previous studies relying on comparison of ruptured aneurysms to unruptured aneurysms. Although care much be taken in generalizing based on this one case, applying these changes to prior data analysis would require increasing the post rupture variables (to correct to the pre-rupture state). Without this correction, the analysis would under estimate the correlation between high flow variables and the risk of future rupture.

20. Conclusion: • The event of aneurysm rupture in this case showed significant changes in the geometric and hemodynamic variables • These changes would lead to an underestimation of pre-rupture variables if only the post rupture variables were considered as in previous studies. • Qualitatively, intra-aneurysmal flow structures are preserved. • Further studies of cases with pre and post rupture images are needed to allow confirmation and generalization.

21. Thank You To think is to speculate with images Giordano Bruno, 1584