Hemodynamic changes in recurrent intracranial terminal aneurysm after endovascular treatment.

RATIONALE AND OBJECTIVES Multiple cases of recurrence of aneurysms after endovascular treatment have been reported. The purpose of the current hemodynamic study was to identify changes in shear stress and pressure associated with the recurrence of terminal intracranial aneurysms after endovascular occlusion. METHODS Using a finite element method, a pulsed flow with a non-Newtonian viscosity of blood was simulated within the aneurysm cavity. A recurrent terminal intracranial aneurysm of a patient originally treated with balloon occlusion was then studied. This was based on a physiologic pulsatile flow, which was observed in the middle cerebral artery. Before and after the balloon occlusion, local maximum wall shear stress and pressure drop at the neck of the aneurysm were calculated and compared with the normal shear stress. RESULTS Although the maximum shear stress at the right neck of the aneurysm was significantly reduced after balloon insertion, it was still 2.5 times greater than the normal maximum shear stress. This was attributable to the presence of a portion of the aneurysmal neck (residual neck), which was not obliterated by the balloon. The balloon also helped to reduce the maximum pressure inside the aneurysm by approximately 15%. Hemodynamic changes in the residual aneurysm neck, where the shear stress and the pressure are high, and other factors may be responsible for the recurrence of aneurysms after balloon or coil occlusion. CONCLUSION Residual necks after balloon occlusion, coil occlusion, or both are attributable to the geometric orientation of the aneurysm with respect to parent and daughter vessels and the variety of configurations of the balloon and coils used to occlude the aneurysms. Inadequate reduction in local shear stress found in these residual necks is an important factor in the recurrence and rupture of the aneurysm after endovascular occlusion.