Introduction: Treatment of intracranial aneurysms with flow-diverting stents has become more prevalent, but the factors that contribute to treatment outcome are not yet clear. Computational simulations can elucidate mechanisms such as hemodynamic factors that contribute to aneurysm recurrence and treatment outcome. This is the first study to utilize patient-specific boundary conditions to improve model accuracy and determine hemodynamic variables associated with long-term treatment outcomes of the Pipeline Embolization Device (PED) (Medtronic, Dublin, Ireland).
Methods: 19 patients with unruptured intracranial aneurysms treated with pipelines were included. Patient-specific blood pressure and velocity were obtained intraoperatively immediately prior to and following treatment via intravascular Doppler ultrasound to define the computational model boundary conditions. Stent geometry and porosity was obtained via ultra-high resolution Synchrotron X-ray microtomography. Pre-treatment and post-treatment hemodynamic values were calculated. Treatment outcome was determined at 18-month follow-up. Retreatment or recommendation for retreatment during this period was considered a failure.
Results: A significantly greater reduction in aneurysm flow rate, aneurysm wall shear stress (WSS), and viscous dissipation, and a greater increase in neck plane shear stress were associated with PED treatment success (Figure 1). Post-treatment aneurysm flow was not different between groups. No significant difference in averaged-aneurysm neck plane and averaged aneurysm volumes was found between outcome groups.
Conclusions: The results demonstrate that hemodynamic variables contribute to aneurysm recurrence and may be associated with PED treatment outcomes. The hemodynamic findings of the success group support the understanding that PED redirects blood flow along the parent vessel preventing recirculation in the aneurysm allowing for a thrombus initiation and subsequent parent vessel re-endothelialization (Figure 2). Contrarily, persistent flow in the failure group likely prevents this healing process. Proposed mechanisms for this treatment-resistant flow include demand from vessels originating in the aneurysm beyond the stent as well as increased stent porosity along highly-curved vessels.
Patient Care: This study furthers our understanding of the intracranial aneurysm hemodynamic mechanisms that are associated with aneurysm recurrence following treatment with the Pipeline Embolization Device. This work provides a foundation for future clinical integration of pre-operative computational fluid dynamics into the neurological surgeon's armamentarium.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Understand that the Pipeline Embolization Devices redirect blood flow along the parent vessel preventing recirculation in the aneurysm allowing for a thrombus initiation and subsequent parent vessel re-endothelialization.
2) Be familiar with the hemodynamic factors that contribute to aneurysm recurrence and may be associated with Pipeline Embolization Device treatment outcomes.
3) Recognize that a significantly greater reduction in aneurysm flow rate, aneurysm wall shear stress (WSS), and viscous dissipation, and a greater increase in neck plane shear stress is associated with Pipeline Embolization Device treatment success.