The Role of Blood Impulse in Cerebral Aneurysm Coil Compaction: Effect of Aneurysm Neck Size

Endovascular occlusion of cerebral aneurysms with bare platinum detachable coils is now recognized as preferable to surgical clipping (ISUIA Group, 2003, ISAT Group, 2002, Bavinzski et al, 1995, Thornton et al, 2002). Dependent on coil packing density (the ratio of the coil volume deposited in an aneurysm to that of the aneurysm volume), aneurysm location, size and neck width, coil compaction with recanalization of the aneurysm remains in the long-term a major concern. The aneurysm neck size is reported to be the main predictor for aneurysm recanalization (Fernandez-Zubillaga et al, 1994). The forces exerted on the coil mass at the aneurysm neck due to blood pulsatility are larger for wide neck aneurysms as compared to small neck aneurysms (Bavinzski et al, 1995). However, impingement forces have not been evaluated. We evaluated the force impinging on the aneurysm neck in a simplified aneurysm (basilar top) geometry utilizing the impulse-momentum equation and Womersley’s flow. Maximum impingement force as a function of aneurysm neck to parent lumen diameter ratio varies as a sigmoid curve. Analysis of the hemodynamic forces affecting coil compaction in cerebral aneurysms shows that the coil mass at the aneurysm neck may be subjected to cyclic impulse impingement due to redirection of blood momentum. Orientation of the aneurysm neck and the main axis of the aneurysm in relation to the oncoming parent vessel flow may help clinicians predict the risk of coil compaction and the location of subsequent aneurysm recanalization.