Predictors of treatment failure following coil embolization of intracranial aneurysms

We present a retrospective review of 357 consecutive patients with 419 aneurysms treated with coil embolization. Although incomplete occlusion and recurrence of intracranial aneurysms following coil embolization is a well-known problem, the factors that influence and predict treatment failure are still debated. For this study, we excluded non-coiling endovascular techniques (flow diversion) and non-saccular aneurysms (fusiform). The modified Raymond-Roy occlusion classification (MRRC) was used to grade the aneurysms. Treatment failure was defined as filling of the aneurysm dome (MRRC Class IIIa or IIIb) at the first angiographic follow-up (average 8 months). Univariate statistical tests were employed to select variables for incorporation into a multivariable logistic regression model. Multivariate analysis identified greater aneurysm volume (p<0.001), packing density (PD) less than 31% (p=0.007) and initial MRRC Class IIIb (p<0.001) as predictors of treatment failure. Incomplete neck coverage with coils was associated with treatment failure in univariate but not multivariate analysis. Class IIIb status was more predictive of treatment failure compared to all Class III (odds ratio 168 versus 14.4). Clinical outcomes were similar in both groups except that there were more retreatments in the treatment failure group (p<0.001). Aneurysm volume, PD and initial occlusion class are associated with angiographic outcome, consistent with prior literature. The MRRC is a powerful predictor of treatment failure. These results will be useful in the effort to both prevent and predict treatment failure after coil embolization, however, they should be verified in a prospective study.