Introduction The recanalization rate of cerebral aneurysms treated by coil embolization has been reported to be as high as 60%. Several characteristics have been shown to correlate with coil compaction and recanalization including: large aneurysm size, wide neck and basilar tip location. In vitro models of side wall aneurysms show that even with maximal packing such that coil herniation into the parent vessel occurs, there remains unfilled volume within the aneurysm. This raises the question of whether or not there is a minimum threshold packing density that should be achieved to prevent recanalization. Further, is there a difference in packing density when an operator is treating a ruptured versus an unruptured cerebral aneurysm?

Purpose To compare the packing density in ruptured and unruptured cerebral aneurysms and to assess whether this impacts on the recanalization rate.

Methods We conducted a retrospective chart review of consecutive patients who presented to University Hospital for treatment of cerebral aneurysms between September 2003 and January 2010. We included only patients that underwent coil embolization for spherical aneurysms in our analyses. We identified 43 cerebral aneurysms of which 23 were ruptured at the time of treatment. Aneurysm volume, coil volume and packing density percentage were calculated using the web based Angiocalc program based on measurements obtained during the treatment angiogram. Follow-up angiograms were obtained for all aneurysms between 3 weeks and 1 year. Aneurysm recanalization was graded using the Raymond Score (RS).

Results We identified 43 spherical aneurysms, 20 of which were unruptured. 76% of the patients were women and mean patient age in the unruptured and ruptured groups were 52 and 51 years, respectively. Linear regression analysis identified a statistically significant correlation between aneurysm volume and coil volume for both the ruptured and unruptured aneurysms (p=0.001 and p=0.023, respectively). In the unruptured group there was a correlation between aneurysm volumes and RS at follow-up (p=0.0074) with smaller aneurysms having durable occlusion at follow-up. Coil volume correlated with RS at follow-up in the unruptured group (p=0.026). Mean packing volume in unruptured aneurysms was 15.97 mm³ versus 45.7 mm³ in ruptured aneurysms but there was no difference in RS between the groups at follow-up.

Conclusion In both groups aneurysm volume was strongly related to coil volume but this did not translate to packing volume percentage. We achieved durable RS occlusion at follow-up, especially in the smaller volume aneurysms. There was a trend towards lower RS scores at follow-up with higher packing volume but this did not reach statistical significance in either group.